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THE NATUKE AND WORK 
 OF PLANTS 
 
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THE NATURE AND WORK 
 OF PLANTS 
 
 An Introductio7i to the Study of Botany 
 
 BY 
 
 DANIEL TREMBLY MACDOUGAL, Ph.D. 
 
 DIRECTOR OF THE LABORATORIES, NEW YORK 
 BOTANICAL GARDEN 
 
 THE MACMILLAN COMPANY 
 
 LONDON : MACMILLAN & CO., Ltd. 
 
 1900 
 
 All rights reserved 
 
COPYKIGHT, 1900, 
 
 By the MACMILLAN COMPANY. 
 
 Nortoooi ^tesB 
 J. S. Gushing & Co. - Berwick & ! 
 Norwood Mass. U.S.A. 
 
PREFACE 
 
 The course outlined in this little book is essen- 
 tially a study of the functions or action of the 
 plant, and organs are considered chiefly as instru- 
 ments for the performance of work, with but little 
 attention to their morphology. It is believed that 
 this method of introduction to the subject of botany 
 will be best suited for beginners who have not at 
 hand the facilities of a laboratory. In conformity 
 with this idea, the use of technical terms has been 
 restricted to the actual necessities of logical treat- 
 ment, and the demonstrations have been developed 
 by the simplest experimental methods. 
 
 Material. — The apparatus needed to carry out 
 the work may be found in any household, with the 
 exception of the hand lens, which may be purchased 
 for less than a dollar; a glass wdiich will magnify 
 six to ten times will be sufficient. A supply of 
 plant material is, of course, indispensable. Stu- 
 dents having access to greenhouses will be able to 
 
 QKnu 
 
vi PREFACE 
 
 secure specimens to illustrate the entire course with- 
 out difficulty. If the plants of the woods and fields 
 are to be used, as many observations as possible 
 should be carried out in the summer, spring, and 
 autumn, and a supply of roots, corms, tubers, bulbs, 
 seeds, and fruits, should be collected for use during 
 the winter season. Many of these may be preserved 
 in the same manner as potatoes, and forced to grow 
 when brought into a warm living-room in January 
 or later. This may be done with the material used 
 in the following paragraphs: 8, 10, 13, 19, 26, 38, 
 39, 43, 44, 45, 46, 47, 48, 50, 51, 53, 54, 77, 97, 106, 
 108, 109, 120, 129, 148, 165, 167, 168, 169, 180, 181, 
 182, 183, 184, 185, 195, 211, 212, 213, 214, 216, 
 217, 225, and 229. 
 
 Desirable material may be obtained from dealers 
 in native plants if the student is unable to collect it 
 himself. It is quite imj)ortant that the plants used 
 should be properly identified, and this may be done 
 by the use of a manual of the flora of the region in 
 which the work is done, which may be selected from 
 the following list : — 
 
 Britton and Brown, Flora of the Nortliern States and 
 Canada, Charles Scribner's Sons, New York. 
 
PREFACE Vll 
 
 Gray, Manual of Botany, American Book Company, New 
 
 York City. 
 Chapman, Flora of the Southern States, Cambridge Botanical 
 
 Supply Company, Cambridge, Mass. 
 Coulter, Flora of Western Texas, United States Department 
 
 of Agiiculture, Washington, D. C. 
 Greene, Manual of Botany of the Region of San Francisco 
 
 Bay, Cubery & Co., San Francisco. 
 Howell, Flora of Northwest America. 
 Coulter, Manual of Eocky Mountain Botany, American Book 
 
 Company, New York City. 
 Gray, Field, Forest, and Garden Botany, American Book 
 
 Company, New York City. 
 
 It will also be found profitable to read the dis- 
 cussions of the various subjects in the following 
 works, which may also suggest furtlier lines of 
 experimentation : — 
 
 Kerner and Oliver, Natural History of Plants, Holt & Co., 
 
 New York City. 
 Coulter, Plant Relations, D. Appleton & Co., New York City. 
 Barne.s, Plant Life, Holt & Co., New York City. 
 Bailey, Lessons with Plants, Macmillan Company, New York 
 
 City. 
 Atkinson, Elementary Botany, Holt & Co., New York City. 
 MacDougal, Experimental Plant Physiology, Holt & Co., 
 
 New York City. 
 Arthur and MacDougal, Living Plants and their Properties, 
 
 Morris & Wilson, Minneapolis. 
 
VlU PREFACE 
 
 The author acknowledges substantial aid from Pro- 
 fessor Francis E, Lloyd in the revision of the man- 
 uscript and the reading of proof, and many valuable 
 suggestions from Mrs. E. G. Britton. 
 
 D. T. McD. 
 
 New York Botanical Garden, 
 January, 1900. 
 
CONTENTS 
 
 I. The Composition and Purposes of Plants 
 
 1. The plant is composed of living matter .... 
 
 2. The purposes of plants 
 
 3. Great differences among plants 
 
 4. The oaks, maples, elms, ferns, mosses, and pond-scums are 
 
 not all of the same kind among themselves . 
 
 5. A species 
 
 6. Scope of w^ork described 
 
 PAGE 
 
 1 
 
 II. The Material of which Plants are made up 
 
 § 7. 
 
 §10. 
 §11. 
 §12. 
 §13. 
 §14. 
 §15. 
 § 16. 
 §17. 
 §18. 
 
 The plant is an engine 
 
 Water, charcoal, and ash 
 
 Leaves shrink in drying 
 
 Mineral coatings .... 
 
 Uses of mineral coatings 
 
 Aquatic plants with mineral coatings 
 
 Water cultures, with and without mineral salts 
 
 Ash or mineral salts in the water of streams 
 
 Elements found in plants .... 
 
 Substances serving as food .... 
 
 Compounds in the plant .... 
 
 Tests for the contents of plants . 
 
 III. The Manner in which Different Kinds of Work 
 
 ARE divided among THE MEMBERS OF THE BODY 
 
 § 19. Kinds of work, or functions of the plant .... 21 
 §20. Organs 22 
 
X CONTENTS 
 
 PAGE 
 
 § 21. Tissues 22 
 
 § 22. Method of study of functions and organs .... 23 
 
 IV. The Roots 
 
 § 23. Functions of roots 24 
 
 § 24. Roots hold the stem firmly in position .... 24 
 
 § 25. Roots were first developed for fixation .... 26 
 
 § 26. Shrinkage of roots to aid in fixation 27 
 
 § 27. The structure of the root 28 
 
 § 28. Climbing roots 28 
 
 § 29. Stilt roots 29 
 
 § 30. Columnar roots 29 
 
 § 31. Keel or ballast roots 30 
 
 § 32. Substances of which the soil is composed . . . . .30 
 
 § 33. The soil and root-hairs adhere 31 
 
 § 34. Root-hairs and the region from which they arise . . 31 
 
 § 35. Action of roots which have been deprived of hairs . . 32 
 
 § 36. Can water be taken through the leaves ? . . . .33 
 
 § 37. The manner in which root-hairs take in liquids . . 34 
 
 § 38. Action of sugar 35 
 
 § 39. Another method of imitation of the action of root-haii-s . 35 
 
 § 40. Action of root-hairs on particles of mineral substance . 36 
 
 § 41. The fate of the particles of soil 37 
 
 § 42. Food-material in the soil, and how the plant finds it . 38 
 § 43. The tips of primary or main roots point downward . . 39 
 § 44. The tips of branches of the main roots are directed hori- 
 zontally 39 
 
 § 45. Sensitiveness of the roots to moisture .... 40 
 
 § 46. Roots bend away from light 41 
 
 § 47. The tip of the root is protected by a sheathing cap . . 42 
 
 § 48. The sensitiveness of roots to touch with solid objects . 43 
 
 § 49. The roots of air-plants 44 
 
 § 50. Parasitic roots 45 
 
 § 51. IMethod of germination and growth of the dodder . . 46 
 
 § 52. Union of roots with fungi 47 
 
 § 53. Roots as storage organs 48 
 
CONTENTS 
 
 § 54. Method of growth of roots .49 
 
 § 55. Absorbing and fixing organs of the lower plants . . 50 
 § 56. Absorbing and fixing organs of the ferns, mosses, and 
 
 liverworts 50 
 
 § 57. Method of fixation of the moulds and mushrooms . . 51 
 
 v. The Leaves 
 
 § 58. Absorption and fixation by the algae and bacteria . . 52 
 
 § 59. Structure of leaves 54 
 
 § 60. Leaves with both surfaces alike 56 
 
 § 6L Compound leaves 56 
 
 § 62. Composition of the air 57 
 
 § 63. Gases of use to the plant 57 
 
 § 64. Functions of the leaf 58 
 
 § 65. The colors of leaves 58 
 
 § 60. Hidden chlorophyl 59 
 
 § 67. Characteristics of chlorophyl 60 
 
 § 68. Spectrum of chlorophyl 60 
 
 § 69. The leaf is a machine or mill 61 
 
 § 70. Quality of light most useful to the plant .... 61 
 
 § 71. Light destroys chlorophyl 62 
 
 § 72. Light is necessary for the formation of chlorophyl in most 
 
 instances 62 
 
 § 73. Capacity of leaves for the absorption of light ... 63 
 
 § 74. Formation of food in chlorophyl-bearing organs . . 64 
 
 § 75. iSTon-green colors 65 
 
 § 76. Origin of red colors 65 • 
 
 §77. Changes in color 66" 
 
 § 78. Autumnal colors 67' 
 
 § 79. Uses of autumnal colors 68 
 
 § 80. Uses of red and other colors in flowers and fruits . . 68 
 
 § 81. Characteristics of red and blue colors .... 69 
 
 § 82. Red color as a shield 69 
 
 § 83. Red color as a heat producer . . ' . . . .69 
 
 § 84. Red color as a heat saver 70 
 
 § 85. Hairs as a protection to a leaf 71 
 
Xll CONTENTS 
 
 PAGE 
 
 § 86. White surfaces 71 
 
 § 87. The positions of leaves 72 
 
 § 88. Length of petioles 72 
 
 § 89. Leaf mosaic 72 
 
 § 90. Getting in the proper position 73 
 
 § 91. Heliotropic movements 73 
 
 § 92. Movements of leaves and stems in response to gravity . 74 
 
 § 93. Movements to avoid injury 74 
 
 § 94. Compass plants 75 
 
 § 95. Some plants have lost the power of manufacturing chlo- 
 
 rophyl 76 
 
 § 96. An association without chlorophyl 77 
 
 § 97. Pitchered leaves 77 
 
 § 98. Food-building in the lower forms 80 " 
 
 § 99. The leaf and water 81 - 
 
 § 100. Course of the water in the leaf 81 ' 
 
 § 101. Transpiration 82 - 
 
 §102. The vapor transpired 82- 
 
 § 103. Measurement of the amount of water thrown off by a 
 
 plant 83- 
 
 § 104. Sunlight increases transpiration 83 
 
 § 105. Regulation and control of transpiration .... 84 
 § 106. Wax or bloom as a means of prevention of excessive loss 
 
 of water 84- 
 
 §107. Size of leaves and dryness of the air .... 84- 
 
 § 108. Sleep movements 85 
 
 § 109. Velvety surfaces 85 
 
 § 110. Autumnal leaf fall 86 
 
 § 111. Separatory laj^er 86 
 
 § 112. The length of life of leaves 87 
 
 § 113. Growth of leaves 87 
 
 § 114. Wilting 88 
 
 § 115. Transplanting trees and herbs is attended by wilting . 89 
 
 § 116. Freezing and frosting 89 
 
 § 117. The air is colder on a frosty night near the surface than 
 
 it is a few feet above it 91 
 
 § 118. Drainage of cold air 92 
 
CONTENTS 
 
 VI. Stems 
 
 §119. 
 §120. 
 § 121. 
 §122. 
 § 123. 
 §124. 
 § 125. 
 § 126. 
 § 127. 
 § 128. 
 § 129. 
 § 130. 
 §131. 
 §132. 
 §133. 
 §134. 
 §135. 
 §136. 
 §137. 
 §138. 
 §139. 
 §140. 
 §141. 
 §142. 
 § 143. 
 §144. 
 §145. 
 §146. 
 §147. 
 §148. 
 §149. 
 §150. 
 §151. 
 §152. 
 §153. 
 
 The nature of stems 
 
 Stems are made up of sections or internodes 
 Branches arise at the nodes or joints only 
 Relation of the leaves and branches . 
 
 Leaf traces 
 
 Relation of leaves and flowers . 
 Structure of stems .... 
 
 Uses of stems 
 
 Methods by which firmness is secured 
 Arrangement of dead cells to secure firmness of stems 
 Arrangement of mechanical tissues in a stem of a grass 
 Mechanical tissues in a sunflower stem 
 Mechanical tissues in a cai-nation stem 
 Arrangement of mechanical tissues in a petiole 
 The firmness of plants that become limp when dried 
 Stems as conducting organs 
 
 Upward path of sap 
 
 Path of sap in large trees .... 
 
 Girdling 
 
 Downward path of material from the leaf 
 
 Forces which carry the sap upward through the stem 
 
 Root, or bleeding pressure 
 
 The flow of sap of the sugar maple . 
 
 Dew 
 
 How to cause a plant to form dew at any time 
 Lifting power of leaves and branches 
 Growth of stems .... 
 
 Action of embryonic tissue of a tree 
 Growth in length and diameter 
 Measurement of growth in length 
 Measurement of growth in diameter 
 
 The bark 
 
 Growth of a corn stem 
 
 Nodding or circular movements due to unequal growth 
 
 Length of life 
 
XIV CONTENTS 
 
 PAOB 
 
 § 154. Annuals 113 
 
 § 155. Biennials 114 
 
 § 156. Perennials 114 
 
 § 157. Changes in the length of life of a species . . . 115 
 
 § 158. Buds 115 
 
 § 159. Naked buds 116 
 
 § 160. Scaly buds 116 
 
 § 161. Buds of the apple 117 
 
 § 162. Buds of elder, maple, or elm 118 
 
 § 163. Sleeping buds 118 
 
 § 164. The awakening of sleeping buds 118 
 
 § 165. Winter buds of aquatic plants 119 
 
 § 166. Behavior of the hibernacula 120 
 
 § 167. Bulbs 121 
 
 § 168. Corms 121 
 
 § 169. Forcing or inducing an earlier growth .... 121 
 
 § 170. Some protective devices of the shoot . . . .122 
 
 § 171. Branches used as leaves 124 
 
 § 172. The part of stems in the struggle for existence . . 124 
 
 § 173. Weeds 125 
 
 § 174. Climbing plants 125 
 
 § 175. The irritability or sensitiveness of stems .... 127 
 
 § 176. Sensitiveness to gravity 128 
 
 § 177. Stems are found among the higher plants only . . 129 
 
 VII. The Way in which New Plants Arise 
 
 § 178. Distribution of the individuals of a species . . . 130 
 
 § 179. Methods of reproduction 131 
 
 § 180. Reproduction by cuttings 132 
 
 § 181. The stem may reproduce the entire plant . . . 132 
 § 182. The root may reproduce the entire plaut .... 132 
 § 183. Structures used by plants as means of vegetative repro- 
 duction 133 
 
 § 184. Tubers 133 
 
 § 185. Bulbils and bulblets 134 
 
CONTENTS 
 
 XV 
 
 § 186. Division of the body by the death of part of it 
 § 187. Division among the simple plants 
 
 § 188. Runners 
 
 § 189. Stolons 
 
 § 190. Dissemination or spreading of the plant by 
 
 propagation 
 
 § 191. Gemmae 
 
 § 192. Reproduction by spores 
 § 193. Reproduction by eggs 
 
 § 194. Fern spores 
 
 § 195. Germination of spores 
 
 § 190. Another form or generation of the fern 
 
 § 197. Alternation of generations 
 
 § 198. The two generations of the moss 
 
 § 199. Occurrence of generations . 
 
 § 200. The generations of seed plants . 
 
 § 201. The gametophyte, or egg-bearing generation in the 
 
 plant 
 
 § 202. The structure of a flower . 
 § 203. The spores of seed plants . 
 
 § 204. Pollination 
 
 § 205. The wind as an aid to pollination 
 
 § 206. Animals as pollen carriers 
 
 §207. Fertilization 
 
 vegetative 
 
 seed 
 
 VIII. Seeds and Fruits 
 
 § 208. The seed 
 
 § 209. The existence of the seed . 
 
 § 210. Fruits 
 
 § 211. The cocoanut .... 
 
 §212. The date 
 
 § 213. Maize, or Indian corn 
 
 § 214. The fruit of the clot-bur, Xanthium 
 
 § 215. Xature of the fruits of Xanthium 
 
 §216. The apple 
 
 § 217. The bean and pea 
 
XVI 
 
 CONTENTS 
 
 IX. The Power or Energy of the Plant 
 
 § 218. Energy of the plant 
 
 § 219. Sources of energy 
 
 § 220. Sunlight as a source of energy . 
 
 § 221. Chemical compounds as a source of energy 
 
 § 222. Physical attraction as a source of energy 
 
 § 223. Release of energy 
 
 § 224. Respiration, or breathing .... 
 
 § 225. Changes in the air produced by breathing 
 
 § 226. Plants by day and by night 
 
 § 227. Relation of the living world and the atmosphere 
 
 § 228. Energy of physical attraction .... 
 
 § 229. Outward work accomplished by physical attraction 
 
 PAGE 
 
 182 
 182 
 183 
 183 
 184 
 184 
 184 
 185 
 186 
 187 
 189 
 190 
 
 X. Relations of Plants to Each Other, and the 
 Place in which they Live 
 
 § 230. Societies and communities 191 
 
 § 231. Plant societies 192 
 
 § 232. Foundations of society 192 
 
 § 233. Communities change 193 
 
 § 234. AVater and plants 194 
 
 § 235. Temperature and plants 194 
 
 § 236. The soil and plants 195 
 
 § 237. Light and plants 195 
 
 § 238. Wind and plants 196 
 
 § 239. Forests . . . . . ... . . .196 
 
 § 240. Relations of members of the forest 201 
 
 § 241. Time of blooming 201 
 
 § 242. Seasonal activity 202 
 
 § 243. Families and species in a community .... 204 
 
 § 244. Meadows 205 
 
 § 245. Rock societies . .206 
 
 § 246. Pond societies 207 
 
CONTENTS XVU 
 
 PAGE 
 
 § 247. Locations occupied by different kinds of communities . 209 
 
 § 248. Extermination of a forest 210 
 
 §249. Fields 211 
 
 § 250. Course of further study 211 
 
 Index 213 
 
THE NATUEE AND WOEK OF PLANTS 
 
 I. THE COMPOSITION AND PURPOSES OF 
 PLANTS 
 
 1. The plant is composed of living matter. — The 
 tints of a flower, the graceful curves of a twining 
 vine, and the uncouth forms of the cactus claim our 
 attention, because they excite our curiosity and 
 admiration. These and many other features of the 
 vegetable world become of much greater interest, 
 however, when it is learned that the color of the 
 rose, the lacelike fronds of the fern, the imposing 
 trunk of the forest tree, the spines of the thistle, 
 and the juicy sweetness of a berry are all due to the 
 action of a wonderful substance, which is known 
 to be living, and is usually termed protojjlasm. If 
 our studies are extended, we may learn that this liv- 
 ing substance is the most important part of our 
 bodies, as well as those of all other animals and of 
 
 jj, C. StaU Colw 
 
2 THE NATURE AND WOBK OF PLANTS 
 
 plants also. Still further it would be found that 
 protoplasm has certain ways of doing things, certain 
 modes of action, or is governed by a number of laws, 
 no matter whether it is in the body of a plant or 
 animal. Very little is known of the composition of 
 protoplasm, except that a great many kinds of 
 material are used in its construction, and that these 
 materials are blended and woven together in a very 
 complex and intricate manner. Protoplasm is a very 
 delicate and sensitive substance, easily destroyed or 
 injured, hence when it forms the body of a phmt or 
 animal, it is generally necessary for it to construct 
 masses or sheets of lifeless substance, which it fash- 
 ions into tools for the performance of its work, or 
 into coverings which hide it from sight and protect 
 its fragile mechanism from damage by heat, cold, 
 dryness, or other agencies which might crush, tear, 
 or injure it in any manner. The yellowish masses 
 of slimy substance to be seen on decaying logs are 
 the bodies of a slime mould which is composed of 
 naked protoplasm. This organism is so low in the 
 scale of life that it is difficult to say whether it is 
 more like a plant or an animal, and it forms cover- 
 ings for its protoplasm in the reproductive stage 
 only. 
 
COMPOSITION AND PURPOSES OF PLANTS 3 
 
 2. The purposes of plants. — Tlie chief purpose 
 of every individual plant is to give rise to other 
 individuals of the same kind. In carrying out this 
 purpose the protoplasm strives constantly to perfect 
 itself, or rather its tools and organs, and to adapt 
 these more exactly to the conditions of light, mois- 
 ture, temperature, and the food supply under which 
 it is compelled to live. The manner in which the 
 living substance attempts to improve its own mechan- 
 ism and the usefulness of its tools determines the 
 form and structure of its body, and accounts largely 
 for the differences between an oak tree and a violet. 
 
 3. Great differences aynong plants. — It needs but 
 the most casual glance at a field or forest to find 
 that there are many different kinds of plants in 
 it. Thus it is easily seen that some are grasses form- 
 ing a thick velvety carpet of sod on the surface of 
 the soil, while others are trees and send their round 
 trunks a hundred feet into the air. The differences 
 between the grasses and the trees are very great, but 
 all plants are not so much unlike as these two groups. 
 It will be found that there are many kinds of trees 
 and many kinds of grasses. Thus to one familiar 
 with the out-of-door world, the maple tree is not to 
 
4 THE NATURE AND WORK OF PLANTS 
 
 be confused with the oak or beech, or the walnut 
 with the sycamore, wliile the pine and poplar are 
 so unlike that they might be distinguished even at 
 night. In the same manner the mosses and ferns 
 comprise many forms. The simple plants which float 
 upon the surface of the water in ponds also show 
 various colors, shapes, and methods of forming 
 colonies in evidence that they do not all live alike. 
 
 4. The oaks, maples, elms, ferns, mosses, and pond 
 scums are not all of the same kind among them- 
 selves. — Now if one goes through a forest and looks 
 carefully at all of the maple trees he may see in a 
 half day's walk, he will find that they do not all 
 have the same appearance. 
 
 In the Middle states one is very likely to see 
 "sugar maples" (Acer saccharum), large handsome 
 trees, over a hundred feet high, many of them with 
 grayish bark, large leaves, flowers greenish-yellow 
 in color, appearing at the same time as the leaves, 
 and the trunk is very full of a sweetish sap in the 
 spring. On the edges of swamps and in the low 
 grounds will be found other maple trees, with the 
 bark of the twigs quite reddish in color, leaves with 
 sharp-pointed lobes and some hahs on the veins, the 
 
COMPOSITION AND PURPOSES OF PLANTS 5 
 
 flowers yellowisli-red, and appearing before the leaves 
 in the spring. The leaves show the most brilliant 
 colors in the autumn. This is the red maple (Acer 
 ruhrum), and the sugar maple and the red maple 
 trees each constitute a species. The trees of each 
 species live in certain kinds of places, and have 
 distinct forms of leaves, twigs, fruit, and flowers 
 adapted to the conditions under which they exist, 
 and these organs are developed at such season in 
 the two species as will enable each to do its w^ork 
 in the best manner. 
 
 The violets are among the earliest spring flowers, 
 and it would be possible in a great many localities to 
 find some with white, others with blue, and others 
 with yellow flowers. Dig up a specimen of each and 
 lay them side by side on the table or a sheet of 
 paper. Compare the roots, stems, leaves, and flowers, 
 as to their number, where attached, form, and color. 
 
 This will show that the three violets have developed 
 their organs in various manners, and that the three 
 are members of tliree different species of the violets. 
 
 A good conception of the difference between spe- 
 cies may be gained from a comparison of a wild 
 cherry tree with those in any orchard, and of the 
 slippery elm with the white elm. 
 
6 THE NATURE AND WORK OF PLANTS 
 
 5. A sj^ecies. — In an examination of a number of 
 sugar maple or red maple trees it will be seen that 
 they are not all exactly the same size, shape, and 
 color, but that the red maples show some differences 
 among themselves. In the same manner the violets 
 with yellow flowers are not exactly the same shape 
 and size as to leaves and stems. Still the yellow 
 violet plants are more like each other than they are 
 like the blue violets. 
 
 We are now ready to define a species, and can say 
 that a species is a group of individuals very much 
 alike one another, but unlike the individuals of 
 another species. Further, if the seeds of the yellow 
 violet are planted, they will germinate and form 
 plants which are like those from which the seeds 
 were taken. It may then be said that the seeds of 
 any species reproduce or give rise to the same kind 
 of specimens as those which bore the seed. The seeds 
 of blue violets always produce blue violets, those of 
 yellow violets always produce yellow violets, and so 
 on through the whole list of over a hundred thou- 
 sand species of plants which form seeds. The groups 
 of individuals which represent the sjDecies may alter 
 their habits and general appearance, little by little, 
 from generation to generation, until in the course of 
 
COMPOSITION AND PUEPOSES OF PLANTS 7 
 
 a grecit many years individuals are produced quite 
 unlike the originals ; yet there are no abrupt changes 
 or jumps from one form to another. Thus, for in- 
 stance, the belief, quite common in some farming 
 communities, that wheat can be converted into 
 "Chess," or ''Cheat," is founded on an utter impos- 
 sibility. It will be shown later (§ 197) that plants 
 have two generations, or two forms which alternate 
 with each other, and these two forms are quite 
 prominent in the mosses ; but in such cases the two 
 forms are equally invariable and may not be changed 
 quickly or suddenly. 
 
 The chief point of interest in the idea of a species 
 in connection with the work to be followed in this 
 book is the fact that a species is a group of individu- 
 als that are trying to adapt themselves to a certain 
 mode of life by means of the special organs in the 
 forms of stems, leaves, roots, and flowers in the 
 higher plants, and by organs which do the same 
 work among the lower forms. And furthermore, 
 that no two species try to live in exactly the same 
 manner. 
 
 6. Scope of ivorJc described. — The studies de- 
 scribed in the following pages make up an outline 
 
8 THE NATURE AND WORK OF PLANTS 
 
 of examination of the plant at work, and consist of 
 observations on the structure of the organs of the 
 plant machine, the things which the plant may do, 
 the way in which it secures food, avoids injury, and 
 accomplishes reproduction. 
 
 An attempt will be made to determine not only 
 the kinds of work a plant may do, but in some 
 instances the opportunity will be taken to measure 
 the amount it may accomplish in the same manner 
 that the capacity of an engine might be noted. 
 
II. THE MATERIAL OF WHICH PLANTS 
 ARE MADE UP 
 
 7. The plant is an engine. — The plant is a 
 machine, and is composed of many more separate 
 parts than a watch or locomotive. The construc- 
 tion of a watch or locomotive may be learned by 
 tearing one to pieces, or by building it up from its 
 separate parts. After this has been done it is much 
 easier to understand the action of these machines. 
 The same is true of the plant. 
 
 The composition of the plant might be found by 
 separating it into its different substances, after the 
 manner of the chemist, or by building it up from the 
 materials of which it may be composed. Neither of 
 these methods is entirely satisfactory when used 
 alone, because they cannot be completely carried 
 out. The substances or compounds in protoplasm are 
 so delicate that when we seek to separate them they 
 are destroyed. The result is the same as if we 
 attempted to tear down a build hig made of bricks 
 so fragile that they would crumble at the touch ; 
 
10 THE NATURE AND WORK OF PLANTS 
 
 when we have finished we have nothing but a pile 
 of rubbish and dust. 
 
 Then, again, . we cannot actually construct proto- 
 plasm with our own hands; but we may ascertain 
 the substances which should be given to the proto- 
 plasm of a plant in the form of food, in order that it 
 should be able to grow or add to its bulk. While 
 both of these methods are subject to so many errors 
 that they are but of little use separately, yet both 
 together give a fan- knowledge of the composition of 
 the bodies of plants. 
 
 8. Water, charcoal, and ash. — Place enough 
 freshly gathered leaves or stems to make about half 
 a pound in a small tin dish, and set on the pan of a 
 balance. Weigh carefully. Now place the pan on 
 the top of a stove for two or three hours, or in the 
 hot sunlight for twice that time. Weigh again. 
 How much weight has been lost ? Set fire to the 
 dried material and attend to it until it is completely 
 burned, being careful that none of the ash is allowed 
 to escape from the dish. Now weigh again. How 
 much weight has been lost this time ? Clean out 
 the pan and weigh. Subtract the weight of the dish 
 from the figures obtained at each weighing and you 
 
THE MATERIAL OF PLANTS 11 
 
 will have first the weight of the fresh material, 
 about half a pound. Wheu the fresh plant is 
 dried, it needs no demonstration to show that water 
 is driven off, so that the next weight represents 
 the material in the plant after the water is taken 
 away. This dried material is composed of two dif- 
 ferent kinds of substances. When it is burned, 
 one kind, constituting the charcoal, is consumed, 
 leaving only the ash or mineral substances behind. 
 If these weighings are carefully made, it will be 
 found that the water makes more than three-fourths 
 of a growing plant, the charcoal generally less 
 than one-fourth, and the ash only one-fortieth or 
 one-fiftieth of the total weight. The ashes that col- 
 lect in a stove are exactly similar to those obtained 
 in this experiment, of course ; and it is well known 
 that the weight of the ash from a heavy armful of 
 wood is very small. This experiment may also be 
 carried out with a potato, carrot, or turnip. 
 
 The relative amounts of the different groups of 
 substances vary with the species of plants exam- 
 ined and the age of the specimens. The greatest 
 proportion of water is to be found in young shoots, 
 the greatest proportion of charcoal in old woody 
 stems, and the greatest proportion of ash in leaves. 
 
12 THE NATURE AND WORK OF PLANTS 
 
 This last fact is due to the action of the current of 
 water which constantly travels upward through the 
 stem into the leaves where it evaporates and passes 
 off into the air, leaving behind all the mineral sub- 
 stance brought up from the soil. 
 
 9. Leaves shrink in drying. — During the drying 
 process the loss of water brings the particles of 
 which the plant is composed closer together, and it 
 shrinks in size. This may be best seen in leaves. 
 Place a leaf of sunflower or some fresh rapidly grow- 
 ing leaf on a sheet of paper, and trace its outline 
 with a pencil. Now put it between two sheets of 
 blotting paper on which is placed a weight of ten 
 pounds. Replace the blotting paper twice a day for 
 three or four days. Place the dried leaf over the 
 original tracing, and make a second drawing of its 
 outline. The leaf has decreased in length and width. 
 Measure the amount. 
 
 10. Mineral coatings. — During the life of the 
 plant the mineral substances in it are usually dis- 
 solved in water and are not visible. In some in- 
 stances, however, these minerals take the form of 
 small crystals which can be seen Avith the micro- 
 scope. In still other cases the mineral is deposited 
 
THE MATERIAL OF PLANTS 13 
 
 on the outside of the plant as a hard covering 
 easily visible. This is especially true of the scour- 
 ing rush (JEquisetum). A complete coat of silicon 
 covers the surface of the stem and gives a rough 
 feeling when handled. The mineral sheath is so 
 heavy that the tissues of the plant may be de- 
 stroyed and it will remain intact. To demonstrate 
 this, put two or three short pieces of the stem of 
 the scouring rush into a dish or test tube and cover 
 with a mixture of three parts water and one part 
 hydrochloric acid (muriatic acid). Warm the prepa- 
 ration nearly to the boiling point for two hours. 
 Pour off the acid and wash with clean water two 
 or three times. The beautiful silicon sheath may 
 now be handled and preserved in water indefinitely. 
 The silicon sheath may be separated in a still 
 more simple manner if a section of the stem is 
 held in the blaze of a fire or the flame of a lamp. 
 The water will be driven off, the dried material will 
 burn, and then the mineral sheath will reach a red 
 heat, retaining its original shape. This may be 
 preserved dry or in water. 
 
 11. Uses of mineral coatings. — The mineral cover- 
 ing of the scouring rush prevents grazing animals 
 
14 TUE NATURE AND WORK OF PLANTS 
 
 from biting the stems, althoiigli it is not known 
 whether they were formed for thcat purpose or not. 
 In some instances mineral substances are deposited 
 on the bodies of plants in the same way in which 
 they are accumulated on the bottom of a kettle in 
 which water is boiled, and are not only of no use 
 to the plant, but are a detriment to growth and 
 food formation. 
 
 Certain species living in localities where there is 
 but little rainfall and where the air is very dry, 
 however, have a layer of salts on the surfaces of 
 the leaves, which attracts water from the air, thus 
 preventing these useful organs from drying out. 
 The mineral coating of a stem may also serve a 
 similar purpose. 
 
 12. Aquatic species ivith mineral coatings. — Many 
 plants which live in the water cause the mineral 
 matter dissolved in it to be deposited on their 
 surfaces. This may be seen on the pond weeds 
 {Potamogetons), if specimens are taken from the 
 water and allowed to dry. Some of the small 
 threadlike algae are said to be " calcareous " because 
 they are found surrounded by masses of lime of 
 greater bulk than their own bodies. Many of the 
 
TUE MATERIAL OF PLANTS 15 
 
 curious rock formations in the Yellowstone Park 
 are made up in this manner. Some of the powders 
 used to polish metals are taken from deposits in 
 the soil, and they consist of the silicon sheath of 
 minute plants. 
 
 13. '^ Water cultures'' ivith and ivithout mmeral 
 salts. — Fill a quart fruit jar with clean rain water, 
 and a second from a stream or pond. Put in each 
 a freshly cut twig of willow (Salix) or a stem of 
 coleus, and place both in sunlight in a warm room. 
 Replace the water weekly, and clean out the jars. 
 The cuttings will soon begin to grow and form 
 leaves, even if the experiment is performed in 
 winter. Compare the amount of growth in three 
 or four weeks. Have they grown equally ? If a 
 difference is shown in the number and size of the 
 leaves and roots, to what is it due ? The follow- 
 ing demonstration may throw some light on the 
 subject. 
 
 14. Ash or mineral salts in the ivater of streams. 
 — Boil a quart of rain water in a dish with a pol- 
 ished inner surface until the liquid has all disap- 
 peared. Examine the bottom of the dish. Nothing 
 has been left behind, and rain water is seen to be 
 
16 THE NATURE AND WOBK OF PLANTS 
 
 lacking in solid matter which might be used as 
 food by the plant. 
 
 Now boil a quart of water from a stream or 
 pond in the same dish until it has all passed away 
 in the form of vapor. A gray coating remains on 
 the bottom of the dish, consisting of mineral salts, 
 which may be taken up by the plant, and which 
 forms the ash when it is burned. This is identical 
 with the "lime" which is deposited on the inside 
 of tea-kettles in which hard water is boiled. 
 
 15. Elements found in plants. — If a complete 
 chemical analysis were made of the plant, it would 
 be found that it had selected sulj^hur, pliosijhorus, 
 magnesium, calcium, potassium, sodium, and iron 
 from the minerals present and had taken these up 
 in certain proportions most useful to it. Besides 
 these, it also gets nitrogen, chlorine, carhon, hydro- 
 gen, and oxygen from the soil and air. Many species 
 take up quantities of silicon, as did the scouring rush. 
 The seaweeds use iodine and hromine, and still other 
 elements are taken up by a few forms, and may 
 or may not serve as food. Thus many of the grasses 
 and sedges do this, and some of them use the 
 mineral to give a sharp saw-toothed edge to their 
 
THE MATERIAL OF PLANTS 17 
 
 leaves, which cut like knives when drawn care- 
 lessly through the hand. This device may well be 
 a protection against animals, for they will not only 
 not eat such plants, but avoid walking among them. 
 
 The plant may pick up almost any salt in the soil 
 penetrated by its roots, of even such poisonous sub- 
 stances as zi7ic, antimony, arsenic, or cop^^e?'. The 
 wood of large numbers of trees growing in the 
 regions which have copper-bearing rock in the soil 
 may contain as much as one per cent of their dry 
 weight in copper, although this metal is of no use to 
 the plant and is slightly poisonous to it. The same 
 is true in regard to zinc and arsenic. In general, it 
 may be said that no substance is taken up in great 
 proportion unless used as food. 
 
 Animals, especially man, take in substances in 
 food which do not actually enter into the tissues of 
 the body, but promote the digestion and use of the 
 necessary elements. The same will apply in some 
 degree to plants. It is necessary for the proper 
 absorption and use of the indispensable food sub- 
 stances that others should be present with them 
 which are not used. Thus the plant does not use 
 sodium in constructing protoplasm, yet it should 
 have this substance in its food solutions. 
 
18 THE NATURE AND WORK OF PLANTS 
 
 16. Substances servi7ig as food. — A fairly perfect 
 food for the plants in the water culture experi- 
 ment described in § 13 may be made by adding to 
 each quart of rain water put into the jars ten grains 
 each of common salt, plaster of Paris, Uj^som salts, 
 calcium j^^iosjjJiate, and a few drops of iron chloride. 
 It will be noted that common salt is a compound of 
 sodium and cidorine. The sodium does not actually 
 enter into the body of the plant, yet its presence in 
 the food is quite useful. 
 
 17. Compounds in the plants. — The different sub- 
 stances taken up by the plant consist of twelve 
 or thirteen elements, and these are united again in 
 such manner as to form many hundreds of different 
 compounds. The formation of these compounds is 
 generally for some specific purpose. Thus sugar is 
 built up from the carbon, hydrogen, and oxygen taken 
 from the food substances, and it is used in the con- 
 struction of living matter, kept as a reserve material, 
 or it may be sent from one part of the body of the 
 plant to another. Acids are formed for many pur- 
 poses, celhdose for cell walls and coverings for the 
 protoplasm, p)roteins to build up the living substance 
 itself, which is constantly wearing out. 
 
TUB MATERIAL OF PLANTS 19 
 
 18. 7'esis for the contents of the plant. — If a raw 
 potato is crushed in clear water, the latter becomes 
 milky, and by placing some of it in a small glass 
 and holding up to the window, numbers of minute 
 granules may be seen. They are not more than a 
 hundredth of an inch in diameter. If a few drops 
 of a tincture of iodine obtained from a druggist is 
 added to the water, it turns blue, owing to the 
 action of iodine upon starch. Put a drop of the tinc- 
 ture on the cut surface of the potato and note the 
 result. 
 
 Apply iodine to the cut surfaces of stems and roots, 
 and determine the portions in which starch may be 
 found. 
 
 Sugar in sugar-cane, sorghum, fruits, or the sugar 
 beet, or in the sap of the maple, may be detected by 
 the taste, and the sour acids may be found in the 
 same manner. 
 
 If you were to take the plant to a chemical labora- 
 tory, and make a complete chemical analysis of it, a 
 large number of other substances would be found, 
 such as oils, tannins, alkaloids, j^^oteins, mineral 
 salts, etc. 
 
 Animals, including man, have found uses for many 
 of these substances, and species which produce them 
 
20 THE NATURE AND WORK OF PLANTS 
 
 are grown or cultivated in great numbers. It is to 
 be borne in mind that the species was not devel- 
 oped for the purpose of being useful to anything 
 except itself. Man has learned to take advantage 
 of the capacity of the plant for forming certain 
 substances, and cultivates these species in order to 
 get their products. This intelligent action is shared 
 by certain lower animals which cultivate crops of 
 moulds and use them for food. 
 
III. THE MANNER IN WHICH DIFFERENT 
 KINDS OF WORK ARE DIVIDED AMONG 
 THE MEMBERS OF THE BODY 
 
 19. Kinds of work, or fimctio7is of the plant. — 
 In accomplishing the purpose of its existence a plant 
 is compelled to do a large number of different things, 
 or carry on a variety of processes. Chief among 
 these are the absorption of material from which food 
 is to be formed from the soil and air ; the conversion 
 of these substances into compounds suitable for stor- 
 age, transportation, or use by the protoplasm ; the 
 assimilation of the food into the living substance, 
 huilding up and enlarging its bod}^, storing up surplus 
 food for future use, conducting water and other mate- 
 rial from one part of its body to another, digesting 
 the reserve material, such as starch, when needed for 
 food, hreathing, throiving aivay the worn-out and 
 useless material, liolding the body in the proper posi- 
 tion, and finally, and most important of all, taking 
 care that the species is preserved by giving rise to 
 new individuals by means of spores, seeds, imnners, 
 
 21 
 
22 THE NATURE AND WORK OF PLANTS 
 
 offsets, and other structures necessary for the process. 
 In addition, the plant must use a large amount of 
 energy and material in j^^otecting all of its parts 
 from injury or destruction by the climate, other 
 plants, or by animals. 
 
 20. Organs. — In the lower or simpler plants, 
 such as algse and bacteria, all of these different 
 things or functions are carried on by a very small 
 body, often consisting of a single cell that could not 
 be seen by the unaided eye. The whole body is used 
 in carrying on nearly all of the various kinds of 
 work. The " higher " plants are those which have 
 developed separate portions of their bodies, especially 
 suited to one or a few kinds of work. The part of 
 a plant thus devoted to one or to a group oi functions 
 is termed an organ. Thus the root, stem, leaf, and 
 flower are each responsible for certain kinds of work 
 necessary for the welfare of the plant, and they are 
 the principal organs of the higher plants. 
 
 21. Tissues. — If the structure of any of the 
 organs is examined, it will be found that it is made 
 up of a number of different kinds of material. Thus 
 in an elder stem may be found pith, ivood, cambium, 
 and lark. The different masses are made up of dif- 
 
THE DIVISION OF WORK 23 
 
 ferent kinds of cells, and are called tissues. Every 
 tissue has a special share in the work of the organ 
 in which it occurs. The tendency of protoplasm to 
 divide its work among separate organs is one which 
 allows the living matter to carry on all of its 
 functions most economically and efficiently, and it 
 has been the chief principle in the development and 
 evolution of all living things. 
 
 22. Method of study of functions and organs. — 
 It will be found most convenient to take each organ 
 of the higher plants and learn what we may con- 
 cerning the w^ork it does and the way in which it is 
 done. After a fair conception of the nature of the 
 activities of the plant has been gained in this man- 
 ner, it will be possible to understand much more 
 clearly the mode of life of the simpler organisms in 
 which many kinds of work are carried on by the 
 same tissues or even by the same cell. 
 
 An insight of the special capacities of the separate 
 organs will also enable one to understand the w^ork 
 in which the entire body of a higher plant par- 
 ticipates. 
 
IV. THE ROOTS 
 
 23. Functions of the roots. — The higher plants 
 are generally stationary, and do not move around 
 except in the case of aquatics which float from place 
 to place in currents of water. It was found in 
 previous experiments that water which washed the 
 soil in streams contains certain salts which it has 
 extracted from the soil, and that these salts are nec- 
 essary to make up the food of the plant. Further- 
 more, it will be seen by an examination of a few 
 specimens that the roots are the organs which pene- 
 trate the soil to any depth, holding the plant in its 
 place, and it is through these organs that food salts 
 might be taken up. The root then may be credited 
 with two kinds of work : fixation or anchorage, and 
 absorption of food. 
 
 24. Roots hold the stem firmly in positioii. — 
 Grasp the stem of a sunflower, or geranium, or some 
 small plant, and attempt to pull it from the ground. 
 A great amount of force will be necessary, as one 
 
 24 
 
 v. estate Collets 
 
THE ROOTS 25 
 
 may easily learn in " weeding " a flower or garden 
 bed. Try to uproot another specimen by pulling 
 sidewise on the stem, and it will be found even more 
 difficult to accomplish. Now tie a strong cord 
 around the stem of a third specimen, and pass the 
 cord over a thick branch of a tree or the top of a 
 fence. Tie weights or heavy objects to the free 
 end of the cord, and add to them until the plant 
 is torn from the ground. How many pounds were 
 necessary to do this ? If a strong pair of spring 
 scales are at hand, this experiment may be per- 
 formed more exactly. Tie the hook of the instru- 
 ment to the upper part of the stem of a tomato 
 or other small plant, and pull directly upward. Note 
 the number of pounds indicated by the scale as the 
 plant is torn loose. The plant is seen to come away 
 with a mass of earth adhering to the roots. The 
 roots are very plainly organs of fixation, and not 
 only penetrate the soil, but clamp a large mass so 
 that they may not be easily torn up. These organs 
 anchor stems so securely that very heavy action of 
 wind, water, or of animals is necessary to displace 
 them. In a walk through a forest in which trees 
 have been uprooted by storms, note the manner 
 in which the masses of earth are clamped by the 
 
26 THE NATURE AND WORK OF PLANTS 
 
 large roots and«the general shape of the root system. 
 What kinds of trees are most easily blown over? 
 
 25. Boots loere first developed for fixation. — In 
 the development of the plant world, roots were 
 first formed by the protoplasm for the purpose of 
 holding the organism in place, and in some of the 
 simpler forms of plants there are to be seen species 
 in which these organs serve no other purpose. The 
 ribbonlike bodies of the marine seaweeds, the lami- 
 narias which may be a foot, or several hundred feet, 
 in length, are fastened to the rocks by a system of 
 " holdfasts," not much larger than the hand. The 
 great extension of root systems to be seen in plants 
 growing in the soil is chiefly for the purpose of 
 absorption. If the root system of such a species is 
 carefully dug up, it will be found to penetrate the 
 soil to a depth of a few feet, and to extend out sev- 
 eral feet from the base of the stem. Indeed, the 
 total length of the root system generally exceeds 
 that of the stems and branches. It has been found 
 by actual measurement that the roots of a sun- 
 flower placed end to end would reach a distance 
 of hundreds, and those of a squash thousands, of 
 feet. 
 
THE ROOTS 27 
 
 26. Shrinkage of roots to aid in fixation. — Ex- 
 amine the full-grown roots of a hyacinth {Hya- 
 cinthus), calla, or jack-in-the-pulpit (Arismma). A 
 short distance back of the tip the surface appears to 
 be wrinkled. The wrinkling is due to the fact that 
 the root elongates by growth at the tip, and as soon 
 as any portion reaches a certain age, it shortens and 
 causes little folds to appear on the surface tissue, or 
 epidermis. If India-ink marks are placed on young 
 roots, and the distance between them measured be- 
 fore and after wrinkling, it will be found that some 
 shrink one-tenth or even one-fifth of their whole 
 length. If the shrinkage of the root simply pulled 
 it through the soil, it could be of no benefit to the 
 plant and might work damage. The tip of the root, 
 however, is firmly attached by means of the root- 
 hairs, and then this portion is bent around so many 
 small rocks that it is not easily pulled back by the 
 contraction. As a result, the base or upper end of 
 the root with the stem to which it is attached is 
 pulled down into the soil still more firmly. Further- 
 more, if the root has sent out side branches, the soil 
 between the side branches will be clamped between 
 them in a manner well illustrated by the masses of 
 rock and dirt seen adhering to the roots of pros- 
 
28 THE NATURE AND WORK OF PLANTS 
 
 trated trees. The side roots contract in the same 
 manner so that the entire root system is a great com- 
 plex clamp which grasps the soil and rocks very 
 firmly, and thus greatly increases the anchoring 
 power of the underground organs. 
 
 27. The structure of the root. — Examine an old 
 root that has begun to decay. Material from a 
 hyacinth or calla will be suitable. Hold the large 
 end in one hand and strip off the outer delicate tis- 
 sue, when a central cord or fibrous mass will be seen. 
 When the organ is growing rapidly the outer cylin- 
 der of soft tissue absorbs water and expands, stretch- 
 ing the central fibrous cord as one might a rubber 
 string. When the root grows old the outer tissues 
 change their form, allowing the central cord to 
 shorten, and wrinkling the epidermis in the process. 
 
 28. Climhing roots. — A large number of species 
 of the higher plants form long slender stems which 
 are unable to stand upright, and which are specially 
 adapted for attachment to the trunks of trees and 
 6ther tall objects, to which they are fastened by 
 various methods. In many instances roots are de- 
 veloped many feet above the ground, and these 
 adhere to the tree in various ways, holding the stem 
 
THE BOOTS 29 
 
 securely in place. Here the original function of fixa- 
 tion alone is carried on, since generally no opportu- 
 nity is offered to absorb food. So finely are these 
 roots adapted for anchorage in difficult places that 
 they can secure a foothold on the polished surface of 
 a marble column or a sheet of glass. This may be 
 seen in the ivy of the gardeners {Ficus). 
 
 29. Stilt 7Vots. — A special adaptation of the 
 fixative function is to be seen in the roots which 
 start from the stem a short distance above the 
 ground and extend outwardly and downwardly until 
 they enter the soil several inches perhaps from the 
 main stem. Such roots brace the stem, and if the 
 tips form branches after entering the soil, their effi- 
 ciency is still further increased. This may be seen 
 in the wheat, corn, and other grasses, as well as in 
 the palms and the mangroves. Go into a cornfield 
 in early autumn and note the stilt roots. Pull a 
 stalk sidewise and note their action. 
 
 30. Columnar 7^oots. — In many of the forest 
 trees, such as the beech, large roots are formed at 
 the surface which take the form of an upright thick 
 sheet of wood tapering in width toward the outer 
 end where it is covered by the soil. These also 
 
30 THE NATURE AND WORK OF PLANTS 
 
 serve the purpose of bracing the stem against being 
 blown over. 
 
 31. Keel or hallast roots. — Some aquatic plants 
 are in the form of a leaflike stem or a rosette of 
 leaves which floats on the surface of the water, and 
 one or more roots are formed which hang downward 
 in the water, serving to keep the floating parts in 
 proper position, and perhaps also as organs of absorp- 
 tion. The members of the duckweed family (Lenma) 
 and the water hyacinth are good examples of this, 
 and should be examined. 
 
 32. Substances of ivhich the soil is comjyosed. — 
 Examine a half cupful of soil taken from the gar- 
 den, by means of a hand lens, or spread it out on a 
 sheet of glass and hold in direct light. When sepa- 
 rated into small portions with a needle it may be 
 seen to be made u]3 of irregular bodies of various 
 sizes, bits of rock, fragments of leaves, stems, seed 
 coats, splinters of bone, feathers, cast-off shards of 
 beetles, as well as a variety of other matter which 
 will depend on the locality from which the soil was 
 taken. Every particle has a faint shiny appearance 
 which disappears more or less completely if the mass 
 is dried over a hot stove. The shiny appearance was 
 
THE BOOTS 31 
 
 due to a tliin layer of water which surrounded eacli 
 particle. It is this thin layer of water which is 
 taken up by the plant, and it contains the mineral 
 salts of the soil in solution. 
 
 33. The soil and root-hairs adhere. — If the speci- 
 mens which were torn up were examined, it would 
 have been seen, that in addition to the masses of 
 soil clamped by the roots, there was a thin layer 
 immediately surrounding each separate root which 
 did not come away easily. Pull up a young bean 
 plant or any other that may be convenient, and 
 examine the roots with a hand lens. The minute 
 particles of soil are seen to be adherent to small 
 glistening hairs w^iich arise from the root, rather 
 than to the surface of the root itself. 
 
 34. Boot-hairs and the region from ivhich they 
 arise. — The root-hairs are very delicate in structure, 
 and it may be seen very readily that they are not 
 foimd along the entire extent of the root. A better 
 view of these organs may be seen if some are grown 
 where they may not adhere to any solid particles 
 which partially hide them. To do this, cut a cir- 
 cular piece of blotting-paper the size of the bottom of 
 a plate, soak it in water, and lay it in a plate. Drop 
 
32 THE NATURE AND WORK OF PLANTS 
 
 a dozen seeds of wheat or oats or radish on the blot- 
 ting-paper and cover with a glass dish. After ger- 
 mination has proceeded for two or three days, take 
 up one of the seedlings and hold between the win- 
 dow and the eye. Innumerable fine hairs are seen 
 projecting from the roots on all sides. If these 
 were examined with a hand lens, they would be seen 
 to be small tubes. Compare the number of root- 
 hairs near the tip with those of the basal portion of 
 the root : where are they most plentiful ? The tubes 
 are the shape of a finger of a glove, and when thrust 
 in among the hard particles of the soil they take 
 irregular shapes and adhere very closely to the bodies 
 they touch, as may be seen if a thin layer of sand 
 is placed on the paper at the beginning of the 
 experiment. 
 
 35. Action of roots which have heen deprived of 
 hairs, — Perhaps the best method of illustration of 
 the uses of root-hairs is to note the action of a 
 root from which they have been taken. To do this 
 remove a young sunflower plant from the ground 
 and shake and brush all of the soil from the roots. 
 This will carry off all the root-hairs, but if per- 
 formed carefully, will not otherwise injure the roots. 
 
THE BOOTS 33 
 
 Replace the plant in the soil as it was before. It 
 will be seen to wilt, no matter how much water is 
 poured over it. From this it is fair to conclude 
 that a root from which the hairs have been broken 
 cannot absorb enough water to meet the needs of 
 all the leaves and stems. 
 
 The root-hairs serve the general purpose of in- 
 creasing the amount of absorbing surface of the 
 root, and as a general rule they are most plentiful 
 on the roots of species growing in dry soils, and 
 are almost wholly absent from species growing in 
 wet soils, swamps, or in the water. 
 
 36. Cmi ivater he taken in through the leaves? — 
 Plants which are slightly wilted often revive when 
 the leaves are sprinkled. The wetting of the leaves 
 might be of benefit to the plant in two ways : it 
 might prevent them from drying out by losing the 
 small supply of water they are receiving from the 
 roots, or it might allow them to absorb water like 
 the roots. It is popularly supposed that leaves may 
 take up water, and the following test will throw 
 some light on the matter. Place a young potted 
 specimen of geranium or tomato where it may not 
 receive water until it has wilted from thirst. In- 
 
34 THE NATURE AND WOEE OF PLANTS 
 
 vert the pot, and sprinkle the leaves with water 
 four or five times in an hour. Does it recover 
 from wilting ? Place the plant upright and water 
 soil copiously : note result. Repeat the test with 
 other plants and determine the matter fully. Can 
 a plant absorb water from the air in sufficient 
 quantity for its needs through its leaves? 
 
 Still another method for testing the capacity of 
 the leaf for absorbing water consists in floating a 
 wilted leaf of the fuchsia or begonia in a vessel 
 of water, with the upper surface downward, and 
 noting results. 
 
 37. The manner in ivJiich 7^oot-hairs take up 
 liquids. — If you were to place some water on one 
 side of a piece of wet parchment, and some sugar 
 on the opposite side, it would be seen that the 
 water would go through the parchment to the 
 sugar in a very short time. It is by a similar 
 action that root-hairs take water from the soil. 
 The root-hair has the form of the finger of a glove 
 with the walls made of parchment. It is lined 
 with living matter, and is filled with water contain- 
 ing; sus^ar and acids. When the hair touches the 
 thin film of water surrounding the particles of soil 
 
THE ROOTS 35 
 
 the soil water is drawn through the walls into the 
 cavity in the same manner as through the parch- 
 ment. Besides this attractive power of the solution 
 inside the root-hair, the thin layer of living matter 
 lining the wall is of such nature that it attracts 
 water, and it will allow the passage of soil water 
 containing mineral substances ; but will not permit 
 the escape of any of the liquid containing sugar, 
 except in the most minute quantities. The small 
 amount of acid which does escape is seen to act 
 very strongly on the rocks in the soil (§ 40). 
 
 38. Action of sugar. — The manner in which 
 sugar draws water into the root-hair is illustrated 
 by the following method : Cut away the top of a 
 carrot, and dig out a cavity as large as an acorn. 
 Fill the cavity with dry sugar and set aside for a 
 few hours. The sugar will be converted into sirup, 
 having drawn water through the walls of the cells 
 of the carrot. 
 
 39. Another method of imitation of the action of 
 root-hairs. — Select a long, sound potato, and bore 
 a cavity in it reaching from one end nearly to the 
 other, being careful not to split it. Trim the skin 
 from the closed end and shape it so that it will stand 
 
36 THE NATUBE AND WOBK OF PLANTS 
 
 upright in a saucer of water an inch deep. Fill 
 the cavity with sugar. Examine five or six hours 
 later. The sugar will have drawn the soil water 
 from the saucer through the wall and filled up the 
 cavity perhaps to overflowing in a very close imita- 
 tion of the action of a root-hair. 
 
 40. Action of root-hah^s on particles of mineral 
 substance. — The root-hairs take up the thin film of 
 water surrounding each particle of soil, and as the 
 walls of the hair are constantly satm^ated with acid 
 or other substances which will corrode rock, they 
 also dissolve some of it in such manner that it can 
 be absorbed. To demonstrate this action fill a small 
 flower-pot half full of common garden loam, and on 
 top of it lay a piece of marble, an oyster or clam 
 shell with a polished surface uppermost. Cover with 
 three inches of clean sand. Place one or two beans 
 in the sand, and water from day to day. After a 
 few days the seeds germinate and send down roots 
 through the soil, which come in contact with the 
 marble or the shells. Two weeks later remove the 
 marble or shell, wash clean, wipe, and allow to dry. 
 Hold between the eye and a window in such manner 
 that the surface will be seen by a reflected light. 
 
THE BOOTS 37 
 
 Irregular branching lines or roughened areas will 
 show where the roots have touched the polished 
 surface, and the hairs have etched away the niineral. 
 
 41. TJie fate of the 2^(^'^iic^6s of the soil. — The 
 particles of soil may be roughly classed as onineral 
 and organic. The latter comprise the remains of 
 plants and animals as described above, and constitute 
 what is known as humus. The humus is constantly 
 being broken down by the action of the soil bacteria 
 and other minute organisms. This action of the 
 bacteria is to obtain the material necessary for their 
 own food, and in the process great quantities of sub- 
 stance are formed which the higher plants use. The 
 deep layer of decaying leaves and twigs in a forest 
 that has not been burned, or laid bare by grazing 
 animals, is a good example of humus formation. 
 
 The mineral particles may not be said to decay, 
 but they are constantly being broken up. The water 
 in the soil always contains carhonic acid set free by 
 living plants and by the action of bactei^ia on the 
 humus, as well as by the decomposition of certain 
 minerals themselves. Other acids are found in the 
 air and are washed down into the soil by rains. The 
 thin film of water which surrounds each particle con- 
 
38 THE NATURE AND WORK OF PLANTS 
 
 tains these acids, and slowly eats away the outer 
 layers, and wherever the roots or their hairs touch, 
 the corrosion is increased so that each small particle 
 in time is entirely dissolved. The rock particles 
 would thus soon disappear from the soil, but frag- 
 ments are constantly being split from the larger 
 rocks by the action of frost, and heat, and the rend- 
 ing action of large roots, so that the supply is kept up. 
 
 42. Food material in the soil and lioio the j^lctnt 
 finds it. — The substances which are formed by the 
 corrosion of the rocks and the decay of humus are 
 not found everywhere in the same quantity, but are 
 scattered more or less unevenly through the soil. 
 To be of the greatest service to the plant, therefore, 
 the roots must not only absorb substances, but 
 should be able to find the places where they are 
 most abundant. The roots of the higher plants are 
 capable of doing this, and direct their tips into the 
 places which contain the food and w^ater necessary 
 for the plant. In order to be able to accomplish this, 
 these organs have become sensitive to gravity, light, 
 heat, moisture, and chemical substances. Some of 
 the forms of sensitiveness of the root may be easily 
 observed. 
 
THE ROOTS 39 
 
 43. The tijjs of primary or main roots point 
 downivard. — Germinate some peas or beans, as in 
 § 34, and when the first roots are two or three 
 inches in length, thrust a pin through the seeds and 
 fasten to a piece of wood or cork with the tips 
 pointing directly upward. Float the cork or wood 
 in a saucer of water and cover with an inverted 
 tumbler. Examine two to four hours later. The 
 tip will generally be found to be pointing downward, 
 having curved near the apex. This behavior is due 
 to its sensitiveness to gravity. The root tends to 
 place its axis in a position in which the tip is 
 directed toward the centre of the earth. This move- 
 ment is not caused by the weight of the root, and it 
 does not bend like a piece of soft wax, as may be seen 
 if you attempt to bend it back to its original posi- 
 tion. It breaks in consequence of such forcible bend- 
 ing. The curvature of the root is due to the action 
 of certain definite parts designed to do such work. 
 
 44. The tijjs of branches of the main roots are 
 directed hoinzontally. — The downward growth and 
 extension of the first roots formed by a seedling is 
 a necessity for almost all plants. After the main 
 root has bored down into the soil, it finds the food 
 
40 THE NATURE AND WORK OF PLANTS 
 
 substances distributed equally in all directions frc m 
 it. To secure this the branches drive their tips 
 horizontally or nearly so, taking a course nearly 
 parallel to the surface of the soil. The positions 
 attained by these secondary roots may be seen if a 
 young bean or tomato plant is carefully dug from 
 the ground, noting the position of the main roots 
 and the branches as they are exposed to view. 
 
 45. Sensitiveness of the roots to moisture. — Both 
 lateral and main roots may encounter other forces, 
 which cause them to bend away from the direc- 
 tions taken in response to gravity as described in 
 the previous paragraphs. The action of -unevenly 
 distributed moisture may be shown as follows : Place 
 some germinating peas in a deep cigar box full of 
 garden soil. They should be planted in the ordi- 
 nary manner near the middle of the box. Give the 
 seedlings barely enough water to keep the soil moist 
 at one end of the box. Pour the necessary amount 
 from a cup on the soil just inside one end and allow 
 it to diffuse toward the plants. The quantity should 
 be so small that the soil in the other end of the box 
 will become quite dry. After a growth of two weeks 
 turn the box upside down, shake out the plant, and 
 
THE ROOTS 41 
 
 observe the position of the roots. Note the direction 
 of the tips, and compare the number and length of 
 those in the moist end of the box with those in the 
 other end. This sensitiveness of roots to moisture, 
 by which they are attracted toward it, causes cisterns 
 and drains to become filled with the roots of clovers, 
 grasses, willows, and elms. 
 
 46. Boots hend aivay from light. — The course 
 taken by roots in response to gravity and moisture 
 usually leads them deeper into the soil and away from 
 the light, but they have the power of bending away 
 toward darkness if the soil should be taken from 
 above them. This may be demonstrated in the 
 following manner : Tie a piece of muslin over a 
 tumbler and punch a number of holes in it with a 
 bodkin. Fill the tumbler completely full with water. 
 Lay some germinating seeds of the radish on the 
 muslin with the roots directed through the holes in 
 the cloth. Set in a window where it may receive a 
 strong light. Add enough water daily to keep the 
 vessel full. Observe the positions of the roots from 
 day to day. The tips will be seen to be directed 
 away from the point from which the light comes, 
 and they crowd toward the inner side of the tumbler. 
 
42 THE NATURE AND WORK OF PLANTS 
 
 47. The tip of the root is protected hij a sheath- 
 ing cap. — The delicate tip of the root is pushed 
 through the soil very rapidly, and its apex must be 
 protected or it would be torn by the rough edges of 
 the rock particles. This may be readily realized 
 when it is found that the pressure by which the 
 root is driven forward is equal to fifteen or twenty 
 atmospheres, or two or three hundred pounds to the 
 square inch, much greater than that exerted by steam 
 in a locomotive boiler. 
 
 If the root meets a soft or yielding substance, it 
 bores through it precisely as you might push a 
 large needle through the same mass. The young 
 roots of rapidly growing plants are often seen to 
 penetrate soft or decaying wood, or even the large 
 roots of other plants. The actual tip of the root 
 proper is composed of extremely delicate cells, with 
 the thinnest coverings in the way of cell walls, and 
 they would be crushed by the lightest touch of any 
 hard object. These cells are of importance because 
 by theh division the tissues of the new portions of 
 the root are formed. To protect the delicate mass 
 of living matter most roots are furnished with a 
 sheath or ca/9 on the tip. This root-cap has come 
 to serve other purposes as well, and it may be 
 
THE BOOTS 43 
 
 found on aquatics covering the tips of roots which 
 hang down in the water and do not touch any hard 
 object. In such examples the sheath is generally 
 very long, extending back over the younger portion 
 of the root, and as it is filled with bitter substa^nces 
 it prevents swimming animals from eating or injur- 
 ing the tips of the roots. It may be seen with 
 difficulty on land plants, but on aquatics, such as 
 the water hyacinth, it is a fourth of an inch long, 
 and may be pulled off and examined with the eye, 
 or better by the aid of a hand lens. A sketch of 
 the appearance of the root should be made, and a 
 number of species should be examined in search 
 for this protecting cap. 
 
 48. The sensitiveness of roots to touch or contact 
 with solid objects. — The root-cap would not be suf- 
 ficient to protect the tip of the root from all danger 
 of injury if it were pushed forward in a straight 
 line and did not turn aside for an obstruction. As 
 a means of avoiding injury from this cause the 
 root has become sensitive to the touch or contact 
 of hard objects, in such manner that it bends away 
 from them. This may be seen by the repetition 
 01 one of Darwin's classical experiments. Fix a 
 
44 THE NATURE AND WORK OF PLANTS 
 
 seedling to a cork, as in § 43, using a very long 
 pin, but placing the root with the tip pointing 
 downward but not touching the water or the cork. 
 Now cut the smallest bit of paper you can handle, 
 and fasten to one side of the extreme tip by means 
 of gum arable softened in water, or shellac. Observe 
 four or five hours, and a day later, and the apex 
 of the root will be seen to have curved away from 
 the side to which the paper was attached, exactly 
 as it would bend away from a hard object in its 
 path. Some difficulty may be experienced in attach- 
 ing the paper properly, and the experiment should 
 be repeated until some decisive result is at hand. 
 
 49. The roots of air p7«n#s. — There are a large 
 number of species which inhabit the warmer coun- 
 tries that never reach the soil, but live upon the 
 branches of trees, to which they cling by means of 
 climbing roots, such as were mentioned in § 28. 
 They also form long cordlike roots which hang 
 downward sometimes twenty or even forty feet in 
 length, with the diameter of a lead pencil. In 
 some instances these reach the soil, and then 
 branches are formed. Generally, however, these 
 aerial roots are papery white in color and have a 
 
THE ROOTS 45 
 
 curious crinkled appearance, especially in the case 
 of orchids. This is due to the peculiar structure 
 of the outer layers of cells. In fact, these roots 
 have a layer of tissue not found in ordinary roots. 
 This outer tissue is composed of cells, which die as 
 soon as they attain full size, and the walls are 
 left, forming a layer of loose spongy tissue entirely 
 sheathing the root. The sj^ongy layer not only 
 absorbs drops of water which may fall upon it, 
 but will also gather water from the air when it is 
 humid and damp. The species furnished with such 
 roots usually live in localities which have much 
 rain, and their entire supply of water may be 
 gathered in these ways. 
 
 50. Parasitic roots. — Many species have the 
 habit of fastening to the bodies of other plants 
 and drawing a part or all of their water and food 
 from them. They do not need the ordinary soil 
 roots, but have developed special forms which are 
 capable of piercing the bodies of their hosts, as the 
 plants on which they live are called. The mistletoe 
 is an example of this type ; but perhaps the para- 
 site most widely distributed in America is the 
 dodder {Cuscuta), which may be seen in damp 
 
46 THE NATURE AND WORK OF PLANTS 
 
 meadows in July and August, twining around the 
 stems of almost any herbaceous plant, forming 
 numerous coils of yellow or cream-colored flowers. 
 If the host plant is taken up and the nature of 
 the union between the two is examined, it will be 
 seen that the parasitic dodder sends a large number 
 of small blunt projections or knobs of tissue into 
 the stem of the host. These are the roots, and 
 they may arise at any point on the stem of the 
 dodder, and their function is the absorption of the 
 sap of the host plant. 
 
 51. Method of germination and groiuth of the 
 dodder. — The seed of the dodder germinates on the 
 ground, sending up a long threadlike stem which 
 waves about slowly in the air until its tip comes in 
 contact with the stem of another species, when it 
 coils around it and sends out its roots. The roots 
 are seen to arise only at points where the parasite 
 touches the stem of the host. If the seed of the 
 dodder is planted in a pot with a young tomato 
 plant or castor oil plant, this may be observed. It 
 may be seen also that the only root formed at the 
 base of the stem on the germination of the seed is a 
 short peg-shaped structure, and that it simply holds 
 
THE BOOTS 47 
 
 tlie seedling in place until it has found a host to 
 which it can fasten. As soon as this is accom- 
 plished, the soil root and the lower part of the 
 stem of the dodder dies away, leaving it entirely 
 supported on the body of its host. 
 
 52. Union of 7'oots ivitJi fungi. — Quite a large 
 number of the higher plants form what are known 
 as mycorrhizas. A mycorrhiza is the structure which 
 results from the union of roots or absorbing organs 
 with the tubelike hyplice or threads of a mushroom 
 or mould in the soil. This union is of benefit to 
 both the fungus and the higher plant. In some 
 instances the fungus lives inside the root, and in 
 others it forms a layer of threads on the outside. 
 
 If the smaller roots of the beech, oak, or any of 
 the pines are dug up, a number of short club-shaped 
 branches may be seen which are brownish in color. 
 These short branches are inhabited by fungi and are 
 mycorrhizas. A second example may be sought for 
 in the waxy white " Indian pipe " or " corpse plant " 
 [Monotropa) which grows in deep woods. Its short 
 bunches of curiously shaped roots are covered with 
 a layer of felt made up of the threads of the 
 fungus. The higher plant gets practically all of its 
 
48 THE NATURE AND WORK OF PLANTS 
 
 food from the fungus, and it therefore has no need of 
 true green leaves. It has lost these organs in times 
 past because of the very fact that it ceased to use 
 them. It is true of all living things, that as soon as 
 an organ ceases to be used or to be useful, it is devel- 
 oped less perfectly on each succeeding generation of 
 individuals until perhaps only a rudiment remains. 
 This is illustrated by the coral-root {Corallorhiza), a 
 reddish orchid common throughout the Northern 
 states. This plant has not only reduced its leaves, 
 but on account of the activity of the fungus in 
 supplying it with food, the roots have been entirely 
 lost, the fungus of the mycorrhizas now living in 
 the short underground stems which have the appear- 
 ance of a bunch of coral. 
 
 53. Roots as storage organs. — During the sum- 
 mer season the plant manufactures much more food 
 than it can use at that time, and the surplus is 
 stored up until needed. The amount thus accumu- 
 lated is often sufficient to feed the plant through sev- 
 eral successive seasons in case it had no opportunity 
 to make its usual supply. Various parts of the body 
 are selected as places of storage. The beet is an 
 example of a root and a small portion of a stem be- 
 
THE ROOTS 49 
 
 ing used for the storage of sugar. The sweet potato 
 family deposit the reserve food in the form of starch 
 in the roots, which become extremely large, as may 
 be seen in the cultivated form. One of this family, 
 the " man of the earth " {Ipomea pandurata), enlarges 
 the main root and deposits starch and oil in it until 
 it reaches a length of several feet, a diameter of six 
 to eight inches, and weighs as much as twenty 
 pounds. It is to be borne in mind that not all parts 
 of the plant found imderground are roots. Many 
 species have stems which live very much like roots 
 and resemble them in general appearance. They 
 may be separated from them, however, by the 
 absence of the root-cap, and by the fact that they 
 show joints, or nodes, and produce huds, although 
 the roots of the sweet potato are also capable of 
 giving rise to buds. 
 
 54. Metliod of growth of roots. — Another fea- 
 ture which distinguishes roots from stems is the 
 method of growth. Germinate a pea or bean, as 
 shown in § 34, until the main root is two or three 
 inches long, then mark it off in sections a quarter of 
 an inch long by means of lines of India-ink applied 
 by means of a thread or a thin splinter of wood. 
 
50 THE NATURE AND WORK OF PLANTS 
 
 Measure the distance between the marks daily for a 
 week. In what part of the root does most of the 
 growth take place ? Compare with the growth of 
 roots (§ 54), leaves (§ 113), and stems (§§ 144-151). 
 
 55. Absorhing and fixing organs of the lower 
 2)lants. — Roots represent the most highly perfected 
 organs for the fixation of the plant in its position 
 and the absorption of food. In the lower forms, 
 incapable of building such complex organs, these 
 functions must be carried on by simpler structures, 
 which perhaps must take other and additional 
 work. 
 
 56. Ahsorhing and fixing organs of the ferns, 
 7nosses, and Uvenvorts. — Among the ferns, mosses, 
 and liverworts absorption and fixation are carried 
 on chiefly by means of large tubes termed rhizoids, 
 which resemble root-hairs except in size and heavi- 
 ness of the walls, although rootlike organs are pres- 
 ent in some species. Some of these forms are very 
 much like the higher plants, in which instance the 
 large rhizoids are attached to the underground parts 
 like root-hairs. In other instances the plant is in 
 the form of a leaflike body, which lies on the surface 
 of the ground. The rhizoids spring directly from 
 
THE ROOTS 61 
 
 the lower side of the flattened body and penetrate 
 the soil, accomplishing both fixation and absorption. 
 Each little tube is very delicate, yet their combined 
 strength is sufficient to hold the body quite firmly in 
 position. The thin bodies of the ordinary liverwort 
 (Marchantia jjolijmorpha or Conocephalus) should be 
 examined and the character of the rhizoids noted. 
 They will be seen as a tangled mass, to which are 
 adhering great numbers of particles of soil. 
 
 57. Method of fixation of the moulds and 7mtsh- 
 rooms. — Find a number of freshly grown mush- 
 rooms or " toadstools " in the ground in the woods, 
 and carefully dig away the soil from around the base 
 of the stalk supporting the umbrella-like top. Run- 
 ning away from the base of this stalk are a number 
 of ragged-looking grayish strands, and if these are 
 followed out farther, they will be seen to divide and 
 subdivide into still smaller strands. These strands 
 constitute the absorbing and fixing part of the plant, 
 and they are made up of a great number of tulles. 
 Bundles of tubes branch off separately and in small 
 groups all along the main strands, giving them the 
 peculiar ragged appearance. These organs penetrate 
 the soil to great distances, living and growing during 
 
52 THE NATURE AND WORE OF PLANTS 
 
 all of the Wcarm season, absorbing the substances 
 set free by the decay of other plants. At certam 
 times they send up the large branches which are 
 ordinarily know as mushrooms, which bear innumer- 
 able spores, and which reproduce the plant. The 
 mycelium, or mass of tubes, spreads rapidl}^ under- 
 ground, and the mushrooms may appear in the most 
 unexpected places and very suddenly. Like the 
 roots of the higher plants, they are driven upward 
 through the soil with great force, and may be seen 
 to lift stones, large pieces of wood, or heavy clods of 
 earth. Mushrooms have been known to grow up 
 under the stones of the sidewalks in village streets, 
 lifting them from their places and seriously dis- 
 arranging the pavement. 
 
 58. Ahsorptio7i and fixation hy the algce, and bac- 
 teria. — Many of the plants of the lowest groups 
 are completely submerged in water in which their 
 food is dissolved, and as a consequence they absorb 
 food over their entire surfaces. Some of these, espe- 
 cially the bacteria, are in the form of small globular 
 or egg-shaped cells, or in the form of rods joined 
 together in a chain, all floating freely in the water. 
 The function of fixation is clearly absent in most 
 
THE ROOTS 53 
 
 instances, and absorption is carried on by the entire 
 body. Some of these organisms accomplish fixation 
 in certain stages of their existence by means of jelly- 
 like substances outside their walls. Some of these 
 floating forms run out minute threads of protoplasm, 
 with which they lash the water in such manner as 
 to swim from place to place. Others, with single 
 or many celled bodies, make holdfasts, or fixing 
 roots, with which they attach themselves to the 
 rocks or the bottom of the pond or stream. 
 
 A general idea of the nature of these organisms 
 may be gained by an examination of the pond-scums 
 (Spirogyra), which float near the surface, and are 
 made up of a number of long threads, each thread 
 being formed by the division and growth of num- 
 bers of rod-shaped green cells. 
 
V. THE LEAVES 
 
 59. Structure of leaves. — Examine the leaves of 
 the oak, maple, beech, and willow on the stems. 
 The leaf will be found to consist of three principal 
 parts : the hase or portion by which it is attached to 
 the stem, the stalk or j^etiole, and the blade or lamina. 
 The base may take the form of a swelling of the 
 petiole, as in the locust, bean, or sumach, or it may 
 develop small, leaflike appendages, as in the w^illow. 
 Make an examination of the leaf of the willow and 
 draw to show results of observations. 
 
 The petiole is generally in the form of a stalk or 
 stem, though it may be edged or winged, or it may 
 be absent, in which case the lamina of the leaf sits 
 directly on the stem. Find some jDlant the leaves of 
 w^hich are lacking in petioles, and draw. 
 
 The base and the petiole are for the purpose of 
 supporting the lamina in the proper position, and 
 conducting water and food to it. It is in the lamina 
 that the most important work of the leaf is done. 
 
 64 
 
THE LEAVES 55 
 
 Now make a careful examination of the blades of 
 the leaves you have brought together. Trace the 
 exact outlines on a piece of paper. Are the margins, 
 cut to the same pattern ? Compare the upper and 
 lower sides of the leaves. The upper side is fairly 
 smooth and even, while the lower is rougher and 
 shows numbers of ridges or nerves, which may be 
 seen only faintly on the upper side. Fill out the 
 outline of each leaf with a tracing of the nerves. It 
 will be found that the nerves start from the base of 
 the leaf or from a median midrib and divide and 
 subdivide, running to all parts of the blade. The 
 space between the nerves is filled by a soft green 
 tissue, the mesojjliyl, and the nerves serve as a 
 framework to hold it in position. By searching 
 among the beds of dead leaves in the woods old 
 specimens may be found from which the mesophyl 
 has decayed, leaving the network of the nerves 
 almost entire. The lower surface of the leaf is fur- 
 nished with thousands of minute openings, the 
 stomata. These are usually so small that they may 
 not be seen even with a hand lens ; but if some of the 
 flattish fronds of the liverwort (Conocejjhalus) can 
 be found, they may be seen on the upper surface 
 with the naked eye. 
 
66 THE NATURE AND WORK OF PLANTS 
 
 The entire leaf, as well as that of the body of 
 the seed-plant, is covered with a thin sheet of cells, 
 the epidermis. The epidermis may be peeled off in 
 whitish strips by using a needle, or point of a sharp 
 knife. 
 
 60. Leaves with both surfaces alike. — The leaves 
 examined in the preceding paragraph are held in a 
 horizontal position on the stems. Examine leaves 
 that are held in an upright position or nearly so, like 
 those of the narcissus, iris, or lily. The nerves will 
 not be so apparent, and both surfaces present nearly 
 the same appearance and would show about the 
 same arrangement of the cells. 
 
 61. Compound leaves. — Examine the leaves of 
 the locust, pea, bean, or sumach. The three principal 
 parts may be found, but the lamina appears to be 
 branched or cut up into a number of smaller leafiets, 
 each with its own stalk by which it is fastened to 
 the midrib or r^hachis of the leaf. The number of 
 leaflets in the bean is three (see also § 217). Deter- 
 mine the number in the locust, pea, and other speci- 
 mens you may find. The compound leaf is capable 
 of doing more work than the simple forms showing 
 the same extent of lamina. 
 
THE LEAVES 57 
 
 62. Comjjosition of the air. — The leaves are 
 generally held aloft in the air, and since they come 
 into contact with no other medium, it is plain that 
 the composition of the air will be of great interest 
 to any one studying the activity of leaves. The air 
 is made up of nitrogen, carbonic acid gas, oxygen, 
 argon, and perhaps other rare gases in small quanti- 
 ties. Besides, watery vapor, and traces of acids are 
 present in a proportion which varies greatly with the 
 locality. In 10,000 gallons of ordinary air would be 
 found about 7795 gallons of nitrogen, 2061 gallons 
 of oxygen, 4 gallons of carbon dioxide, 140 gallons 
 of water, and small amounts of the other constitu- 
 ents. These gases and vapors are not united to form 
 a compound. Thus hydrogen and oxygen are united 
 to form the compound water, but the gases of the air 
 are simply mixed together without actually uniting. 
 
 63. Gases of use to the plant. — The oxygen and 
 carbon dioxide are of the greatest importance to the 
 plant. Nitrogen of the air is of no use, except to 
 mix with and dilute the other gases. Only a few 
 species are capable of taking this gas and using it 
 as food. This element is usually gained from com- 
 pounds in the soil. 
 
58 THE NATURE AND WOBK OF PLANTS 
 
 The water of the air is rarely used by the plant, 
 yet its presence prevents the plant from drying out, 
 and it is of great importance in this way. The other 
 substances are more or less useful or harmful, accord- 
 ing to the quantities present. 
 
 64. Functions of the leaf. — To the leaf is in- 
 trusted the work of taking in the carbon dioxide 
 of the air, splitting it up, and combining it with 
 water sent up from the roots, in such manner as 
 to form sugars. The stream of water also brings 
 up mineral substances from the roots which are 
 needed in the leaf. The amount of water which 
 thus reaches the leaf is much greater than can be 
 used in the tissues, and most of it must be thrown 
 off. This is also done by the leaf, 
 
 65. The colors of leaves. — The leaves of most 
 species are colored green by the presence of a sub- 
 stance the botanist terms chlorophyl, and this pig- 
 ment is also found in the outer tissues of some stems, 
 branches, or even roots. It is formed in special 
 masses of protoplasm, and the depth of the green 
 color of the leaf depends on the number of these 
 masses in the cells. Then again the living matter 
 
THE LEAVES 69 
 
 has the power of moving the masses of pigment 
 toward and away from the surface so that the tone 
 of color may change in the same leaf during the 
 course of a few hours. 
 
 Besides the green, other coloring matter may be 
 present in the cells, or the walls may be dyed. The 
 leaf may show a certain color because of the contents 
 of its cells, or because of the color of its walls, in 
 the same manner that a bottle of liquid may appear 
 blue because of the color of the liquid, or the tint 
 of the glass. 
 
 66. Hidden chlorophjl. — Chlorophyl may be 
 hidden because of the presence of other colors. 
 The leaves of the amaranth, cockscomb, and many 
 other species appear to be dark red in color, and no 
 chlorophyl is to be seen. That it is j^i'esent, how- 
 ever, may be shown by the following experiment: 
 Place a colored leaf as above, in a dish of cold water, 
 and bring it to a boil over a stove or spirit lamp. If 
 this is continued for a few minutes, the red color 
 will be extracted, and the normal green of the leaf 
 will be visible. The experiment also shows that red 
 coloring matter is soluble in water, while chlorophyl 
 is not. 
 
60 THE NATURE AND WORK OF PLANTS 
 
 67. Characteristics of chloi^ojyhyl. — Chloropb.yl is 
 absolutely indispensable for the formation of food in 
 the leaf, and it will be important to extract some of 
 it from a leaf and ascertain its qualities. To do this 
 place a. number of leaves, that have been cut up into 
 small pieces or bruised, in a bottle or tumbler and 
 cover with alcohol. Close the vessel and set away 
 in a dark place for a day. Pour off some of the 
 liquid into a wine-glass or small test tube. Hold up 
 to the light. The solution appears to be of a bright 
 emerald green. Now hold the glass in direct sun- 
 light and look at the edge of the liquid. If held 
 properly, it will show a blazing red appearance. 
 Chlorophyl has the power of making such changes 
 in sunlight that it appears red; it affects light in 
 other ways also. 
 
 68. S2:)ectrum of chlorophyl. — If the study of 
 chlorophyl were continued in the physical labora- 
 tory, it could be seen that if light which has passed 
 through a solution of chlorophyl is spread out on a 
 screen by means of a prism of glass, some of the 
 colors of the artificial rainbow will be missing. The 
 missing parts will comprise the blue, violet, and most 
 of the red rays. Chlorophyl, in the living plant, ab- 
 
THE LEAVES 61 
 
 sorbs these rays, and the energy derived from them 
 enables protoplasm to carry on the work of food- 
 making. 
 
 69. The leaf is a machine or a mill. — If the ac- 
 tivity of chlorophyl might be described in another 
 way, it could be said that the leaf is an engine. The 
 chlorophyl would be the boiler, and when light falls 
 upon it energy or power is set free, which causes 
 the engine to move or perform work, as when heat 
 is applied to the boiler of a steam engine. The leaf 
 is a solar engine and gets its energy from light 
 instead of heat rays. The power acquired from light 
 by chlorophyl drives the protoplasmic machinery and 
 enables it to take water and carbon dioxide and 
 make sugar from them, throwing off certain things 
 not used in the process. After the formation of 
 sugar it is combined with nitrogen and other ele- 
 ments before it can become a part of the living 
 matter. 
 
 70. Quality of light most useful to the plant. — 
 Prepare two boxes of seedlings. The boxes should 
 be at least six or eight inches deep, and the plants 
 should be grown in a thin layer of soil at the bot- 
 tom of the box. Cover one box with a sheet of win- 
 
62 THE NATURE AND WORK OF PLANTS 
 
 dow glass and red tissue paper, and the other with 
 glass and blue paper, and set in a sunny place. Care 
 for the plants from day to day, and compare their 
 growth at the end of a week. This will determine 
 whether the blue or red rays -are most useful to 
 the plant, and will also recall the mistaken "blue 
 glass " craze of a few years ago. 
 
 71. LigJit destroys chlorophyl. — Place a portion 
 of the solution of chlorophyl prepared in § 67 in 
 the sunlight, and the remainder in a dark closet. 
 Compare the color of the two in a few days. The 
 one in the light will be seen to have faded. The 
 fading action of light goes on in the leaf con- 
 stantly, but the green color is constantly restored 
 by the protoplasm. If a plant should be exposed 
 to a light much stronger than that to which it is 
 accustomed, the fading will take place faster than 
 the living matter could mend it, and the leaf would 
 turn yellow and die. 
 
 72. Light is necessary for the formation of chlo- 
 rophyl in most instances. — While light slowly breaks 
 down chlorophyl, yet the plant usually cannot form 
 its substance without the aid of light. Place a 
 bulb of canna, jack-in- the-pulpit, or a seed of the 
 
THE LEAVES 63 
 
 pea or bean in proper soil in a pot and set in a 
 dark cellar and then cover with a bucket or a box. 
 Give the seedling the proper amount of water, which 
 will be less than if grown in light. After a time 
 shoots will be formed which will be very much 
 different from those grown from similar seedlings 
 or plants in the light. 
 
 Lay a broad board on the grass, and note the 
 color of the blades beneath a week later. Not only 
 will the chlorophyl be absent, but the stems and 
 leaves will be greatly changed in form and size. 
 The stems will be two or three times as long as 
 usual. This seems to be a method by which the 
 plant gets its leaves and stems up to sunlight when 
 they are covered by anything or overshadowed by 
 other plants. Species like the narcissus, which have 
 sword-shaped leaves with no petiole or stem above 
 ground, elongate the blade of the leaf itself in this 
 effort to get up to light. 
 
 73. Cajmcity of leaves for the ahsorption of light. 
 — Take any tube of wood, metal, or paper an inch 
 or more in diameter, and fasten a leaf over the end. 
 This may be done by turning the margins back over 
 the tube and tying a string around the tube at that 
 
64 THE NATURE AND WORK OF PLANTS 
 
 point. Hold the tube with this end pointing di- 
 rectly toward the sun, and put the eye at the other 
 end. Can any light be seen through the leaf? If 
 so, add another leaf and test again. How many 
 leaves are necessary to take up all the light? If 
 several kinds of leaves are tested in this way, it 
 will be found that those of different species vary 
 greatly in their light-absorbing power. Do you 
 notice any connection between tliis capacity and 
 the place in which the species grows naturally? 
 
 74. Formation of food in chlorophyl-hearing organs. 
 — The carbon dioxide of the air is used by the 
 plant in making food. This compound consists of 
 two volumes of oxygen and one of carbon. It is 
 taken into the leaf through openings on the lower 
 surface and passes through the thin walls of the 
 cells containing chlorophyl. It is then split in two 
 parts, and the carbon is combined with the oxygen 
 and hydrogen of water to form a sugar. Most of 
 the oxygen is thrown off. All of these steps may 
 not be followed, even in the best-equipped laboratory, 
 but if the leaf of any water plant growing in the 
 sunlight is observed, it may be seen to give off small 
 bubbles of oxygen. This may be best seen by plac- 
 
THE LEAVES 65 
 
 ing a small aquatic plant in a tumbler, or the leaf of 
 a land plant may be immersed in water and the 
 formation of the bubbles noted. 
 
 75. Non-green colors. — If the experiment in § 72 
 is repeated, it may be seen that red and other colors 
 are formed in leaves grown in darkness as well as 
 in light. This may be illustrated still further if a 
 flowering branch of some plant is thrust through a 
 hole in the wall of a tight pasteboard box, and the 
 flowers allowed to open in darkness. The most 
 noticeable of the colors that are found in leaves, 
 beside green, is red, though purples are also abundant. 
 All shades of red, blue, and yellow are to be seen in 
 flowers and fruits. If a clump of rhubarb is made to 
 grow in a dark cellar, the leaves and stems will be 
 blood red. 
 
 76. Origin of red colors. — Red coloring matter 
 is formed most freely in parts of the plant contain- 
 ing much sugar. The origin of coloring matters is 
 not well understood. It has been determined, how- 
 ever, that when a specimen is fed with sugar, it will 
 manufacture this color more abundantly. To demon- 
 strate this action a species should be selected that 
 has the power of making the color, such as ivy, 
 
66 THE NATURE AND WORK OF PLANTS 
 
 Virginia creeper, columbine ; and a cutting composed 
 of a large branch or twig should have the lower end 
 immersed in a stone or glass jar as in the water cul- 
 tures previously described, § 13. The jars should be 
 filled with water from a stream or well to which an 
 ounce of sugar or glucose has been added for each 
 quart. Compare the colors of the leaves with others 
 grown in the same kind of water without sugar, and 
 also with those remaining on the plant. 
 
 This experiment may be repeated if living speci- 
 mens of the bladderwort (Utricularia) can be pro- 
 cured. Place some specimens in a shallow dish of 
 water and set in the sun. Prepare a second dish, but 
 add the proportion of sugar used in the last test. 
 Change the liquids at least once a week. Note the 
 depth of red color of the two specimens. Cold and 
 wounds also induce the formation of red coloring 
 matter. 
 
 77. Changes in color. — The red and blue colors 
 appear to be very closely connected, because the 
 parts of a plant may often change from one to the 
 other in the course of a few days. This may be 
 noticed in the flowers of the peony, as well as in the 
 opening buds of many plants. Note the color of 
 
THE LEAVES 67 
 
 the leaves of the oak and maple immediately after 
 the buds open in the spring, and compare with that 
 of the mature organs. Compare also the colors of 
 ripe and unripe fruits, such as apples, tomatoes, 
 berries, plums, and peaches. 
 
 78. Autumnal colors. — The colors of autumnal 
 leaves are very striking, not only because of their 
 depth and brilliancy, but because they appear on 
 so many leaves and so many plants at the same 
 time. Furthermore, the plants which show colors 
 most notably are trees which are large and prominent 
 features of the landscape. These colors embrace a 
 large number of shades and tints of yellow, red, and 
 purple, and they are probably formed from the sugar 
 in the cells, and by the breaking down of the green 
 color into yellows and browns. Yellow colors are 
 also formed independently, or appear most strikingly 
 in dying leaves. The actual changes of color in at 
 least one species should be followed through the 
 months of September and October, as well as the 
 colors of the same species when the buds open in 
 the following spring. Although the autumnal colors 
 of every species show some diversity, yet the keynote 
 is fairly constant. The birches are a golden yellow, 
 
68 THE NATURE AND WORK OF PLANTS 
 
 the oaks vary through yellow orange to reddish 
 brown, the red maple is generally a scarlet varying 
 to a dark red, the tulip tree a light yellow, and 
 sumachs become a flaming scarlet. These colors 
 show some variation with the amount of moisture 
 and character of the soil. 
 
 79. Uses of autumnal colors. — The actual pur- 
 pose of the autumnal colors cannot be determined. 
 There is no doubt, however, that their presence pre- 
 vents damage by sunlight to delicate substances 
 which are withdrawn from the leaf to the stem 
 before they are cast off. 
 
 80. Uses of red and other colors in flowers and 
 fruits. — The purpose of the brilliant colors of 
 flowers, fruits, and leaves is not clearly made out. 
 The colors of flowers may serve to attract insects, 
 but this is the case in only a few instances An 
 insect is attracted to a flower generally by the scent 
 of nectar or honey, and it recognizes the flower by 
 its size and form rather than by the color. The 
 same is true of fruits which need the aid of insects 
 for their dissemination. It is to be noted that very 
 vivid colors are often found in the centre of large 
 
THE LEAVES 69 
 
 objects, such as the sugar beet, or large fruits, where 
 they could not possibly be of any use whatever. 
 
 81. Characteristics of red and Hue colors. — It 
 has been shown in § 66 that the red color of a leaf 
 of coleus may be extracted by water, and it is a 
 matter of common experience that the colors of fruits 
 are easily obtained in this way. If red coloring 
 matter is examined in the same manner as chloro- 
 phyl, it will be found that it absorbs different rays 
 of light than those taken up by the green pigment. 
 
 82. Red color as a shield. — A great many species 
 are furnished with a layer of red color on the upper 
 side of the leaf. This absorbs some of the light 
 which strikes the leaf, and a diminished amount is 
 allowed to fall upon the delicate green coloring 
 matter below. The action of the red then would 
 be like the slats of a shutter, which permit only a 
 part of the rays to shine through. The presence 
 of the red would be beneficial to leaves exposed to a 
 degree of sunlight stronger than they are otherwise 
 adapted to bear. 
 
 83. Red color as a heat producer. — The rays of 
 light that are taken up by the red and blue colors 
 
iO THE NATURE AND WORK OF PLANTS 
 
 are converted into heat. This may be demonstrated 
 if two naked-bulb thermometers are procured. Next 
 find a species wliich has some of its leaves green and 
 others red, such as canna or coleus. Wrap a green 
 leaf around the bulb of one and secure it with a 
 small string. Place a red leaf around the bulb of 
 the second instrument. Expose them side by side 
 to the sunlight for twenty minutes, then read the 
 height of the mercury in both instruments. 
 
 84. Bed color as a heat saver. — Examine a num- 
 ber of plants growing in a deep forest in the shade. 
 Many of those species which have large leaves 
 lying against the ground, or floating on the water, 
 will exhibit a layer of color on the lower side 
 of the leaf but none on the upper. Light which 
 strikes such leaves will be used partly by the 
 chlorophyl, and the remainder on reaching the lower 
 side of the leaf will be mostly converted into heat 
 by the red pigment. Again, it is to be said that it 
 is not definitely known that the color is formed here 
 for that purpose. The color may be produced as a 
 result of the fact that it is subjected to low tempera- 
 tures at night, but it certainly does bear the above 
 relation to light. 
 
THE LEAVES 71 
 
 85. Hairs as a 2^rotectlon to the leaf. — The leaves 
 of many species, especially those growing in local- 
 ities subject to very intense sunlight, are often 
 clothed with a dense layer of long wavy or branch- 
 ing hairs, and these serve to ward off the fiercer rays 
 and prevent drying out. The same purpose is also 
 accomplished by the development of a very heavy 
 outer cuticle or vvall of the epidermis. 
 
 86. White floivers. — The white colors of flowers or 
 other portions of the plant are due to entirely differ- 
 ent causes. Chief among these is the loose arrange- 
 ment of the cells and the absence of coloring matter. 
 The air between the cells reflects back the light, giv- 
 ing the whitish effect. This may be illustrated by 
 the appearance of a sheet of glass when unbroken, 
 and when crushed or pounded into minute particles. 
 In the first case it shows its natural color and is 
 transparent. When pounded up into a mass of sand- 
 like particles, the light is reflected back from the 
 surface of each, giving the mass a whitish appear- 
 ance. Test the paper-white leaves of any plant you 
 may be able to obtain from a greenhouse and deter- 
 mine to what extent the light penetrates them, as 
 in § 73. 
 
72 THE NATURE AND WORK OF PLANTS 
 
 87. The positions of leaves. — Go out into an open 
 woods or meadow and note the positions of the 
 leaves of all the plants you may see. Select a suit- 
 able specimen and walk around it, noting the posi- 
 tions of these organs on every side of the plant. Do 
 they face all the points of the compass? are they 
 horizontal ? Do you note any connection between 
 their position and that from which the rays of light 
 come ? Does every leaf receive direct sunlight at 
 some time of the day, and at the same hour ? 
 
 88. Length of the petioles. — Take a number of 
 leaves from different parts of the same plant, and 
 compare the length of the petioles. Observe the 
 leaves as they are attached to the stems. Does this 
 inequality of the petiole serve any purpose in connec- 
 tion with the light? Take the long-petioled leaves 
 from some plant and put them in the place of short- 
 petioled leaves on another stem. What is the result, 
 so far as receiving light is concerned? 
 
 89. Leaf mosaic. — A close examination will show 
 that length of stalk and size of blade stand in 
 close relation to each other, and that the distance 
 between the points at which the leaves are fastened 
 to the stems is also a factor in their arrangement. 
 
THE LEAVES 73 
 
 The full effect of each factor may be seen if the 
 arrangement of the leaves of the ivy or some plant 
 which clings closely to a wall is examined. Here 
 each leaf is of such form, size, and length of stalk 
 that it does not seriously overlap or shut the light 
 from any of its neighbors. 
 
 90. Getting in the proper position. — In addition 
 to alterations in the form and size of the stalks and 
 blades in order to get better exposure to light, the 
 protoplasm has the power of moving the petiole and 
 blade in such manner that it will receive the light in 
 the best manner, or the one suited to its capacity. 
 This is done by twisting or bending the stalk or peti- 
 ole, or by bending the stem to which it is attached. 
 
 91. Heliotropic movements. — The action of the 
 leaf or stem for placing the blades in the proper posi- 
 tion for receiving light in response to the sensitive- 
 ness of the plant to light is termed heliotrojnsm. 
 This may be observed in house plants grown by a 
 window. Here all of the leaves have moved in such 
 manner as to make their blades face the window. 
 If such a plant is turned halfway round so that the 
 leaves face away from the window, they will quickly 
 regain their former position. Perform this experi- 
 
74 THE NATURE AND WORK OF PLANTS 
 
 ment with a geranium, and note the position of the 
 leaves five or six hours and a day later. 
 
 Repeat the experiment by bringing a plant from 
 the open air and placing it in a box with one small 
 opening. Sketch the position of the stems and 
 leaves and do the same a day later. In what region 
 has the movement taken place, the leaf stalk or the 
 stem to which it is attached? The movements of 
 roots away from the light, § 46, are to be recalled 
 in this connection. 
 
 92. Movements of leaves and stems in response to 
 gravity. — Many leaves and stems are seen to curve 
 upward without regard to the direction from which 
 the light comes. This power of response to gravity 
 is termed geotrojnsm.. It is this property of the 
 plant which enables it to hold its stems outright. A 
 different kind of geotropism makes the stems of the 
 trailing species lie along the surface of the soil. 
 
 93. Movements to avoid injury. — The rays of 
 light from the sun exert the greatest effect when 
 they strike the surface of a leaf squarely or perpen- 
 dicularly, as any one may know when he recalls that 
 the sun shines the hottest when it is directly over- 
 
THE LEAVES 75 
 
 head. A leaf in the open would receive the greatest 
 amount of light if it were held in a horizontal posi- 
 tion, and as the intensity of the light at noonday is 
 such as to be injurious to many species, they have 
 developed the power of changing the position of the 
 blades at such times. This movement generally 
 consists in tilting, so that the tip points more or less 
 directly upward or downward. In either case the 
 rays of the noonday sun strike the surface at such 
 an acute angle that their effect is not so great. The 
 efficiency of this device can be very readily demon- 
 strated if you should place one tin plate flat upon 
 the surface of the ground, and stand another one 
 upright on its edge, noting the difference in warmth 
 of the two, a half hour later, by the touch. Move- 
 ments of the leaves or leaflets to avoid injury from 
 excessive light may be seen if the bean, locust, pea, 
 or any member of the family should be examined 
 during the warmer part of a summer day. The 
 same plants may also move their leaves to escape 
 dangers of another kind during chilly or cool nights. 
 
 94. ComjKiss lolants. — If the leaves of the wild 
 lettuce, which is now a common weed in the United 
 States, are examined, it will be found that those on 
 
76 THE NATURE AND WORK OF PLANTS 
 
 specimens standing out in exposed places are twisted 
 so that they point nearly toward the north or south 
 — a fact which has given the plant its common name. 
 The effect of this arrangement is to present the edge 
 of the blades to the noonday sun, and the direct rays 
 may strike them only in mid forenoon and mid after- 
 noon, thus avoiding the fiercer rays of the noonday 
 sun. Only a dozen species show this interesting 
 method of avoiding damage to the leaves. 
 
 95. Some plants have lost the poiver of manufac- 
 turing chloroj^hyl. — All species which take carbon 
 dioxide from the air do so by means of the help of 
 chlorophyl, and when they live in a place where 
 they may get their food already formed, the green 
 color is not needed. It is an invariable rule with 
 all living things, that as soon as an organ or a struc- 
 ture or a substance becomes less useful, the succeed- 
 ing generations of the plant do not perfect the useless 
 thing. Hence the species which have become able 
 to take up their food already formed have lost 
 their green color. The bacteria have all done so, 
 as well as the mushrooms, and moulds, and their 
 relatives. A few flowering species have undergone 
 similar changes. If a plant gets its food from the 
 
THE LEAVES 77 
 
 body of another living plant or animal, it is termed 
 a parasite, and a brief study has already been made 
 of some of the characteristics of species of this kind 
 (§ 50). If its food consists of the substance of the 
 decaying bodies of other organisms, it is then termed 
 a saprophyte. Bacteria and mushrooms and moulds 
 offer most of the examples of both classes. 
 
 96. An association ivithout chlorop)liyl. — It has 
 been pointed out in a previous paragraph that some 
 species of higher plants have fungi united with their 
 roots, forming a partnership which is of mutual 
 benefit. This partnership results in the seed plant 
 securing food without making it in the usual manner, 
 so these species lose their green color because of 
 disuse. The leaves also decrease greatly in size, 
 lose some of their tissues, and their characteristic 
 position with regard to light. The Indian pipe, 
 coral root, pine sap, and others are striking illustra- 
 tions of this action. 
 
 97. Fitchered leaves. — Quite a large number of 
 species have changed their leaves in such manner 
 that they serve as traps for catching and holding 
 animals. The bodies of these creatures are digested 
 and used as food. The greatest variety is exhibited 
 
78 THE NATUBE AND WORK OF PLANTS 
 
 in the method of action. Perhaps those most easily 
 found and examined are the traps of the pitcher 
 plant (Sarracenia) and bladderwort {Utriciilaria). 
 The pitcher plant is a member of a family that 
 extends around the globe, and the pitchers of the 
 different members of the family are unlike ; the com- 
 mon pitcher plant, or Sarracenia, is found growing 
 in bogs and swamps over a large part of the United 
 States. A search should be made for them in such 
 places, and fine specimens may be found near tama- 
 rac swamps. They may be easily distinguished by 
 the urn-shaped leaves. When found, note the man- 
 ner in which these leaves arise in clusters from a 
 short underground stem. Note the general form 
 and color of the organs. Beside the green, vari- 
 ous markings of red and purple are to be seen. 
 Note the following regions of the leaf : the 2^etiole, 
 the ^;z7cAer, or urn-sliaped part, and the hood, or lij), 
 at the upper outer edge. Split a leaf from top to 
 bottom, noting the shape of the cavity and the con- 
 tents. What kinds of animals do you find inside ? 
 Next make an attempt to determine the manner 
 in which they were enticed or entrapped in the 
 pitcher. Examine the upper and outer edge of the 
 pitcher for honey. Inside and near the top of 
 
THE LEAVES 79 
 
 the pitcher will be found a zone of bristly hairs, 
 below this a smooth belt, and below this a second 
 zone of hairs. Small animals once descending into 
 the pitchers purposely or accidentally are unable to 
 make their way up again through the downward 
 pointed hairs, or across the glazed surface, and they 
 finally fall into the liquid in the bottom of each 
 pitcher. Glands on the inner surface secrete a diges- 
 tive fluid which dissolves their bodies much like the 
 action of a stomach, and the substances may then be 
 absorbed. Of course not all animals are held by this 
 trap. A winged insect very rarely escapes, however, 
 after its wings are wet by the fluid. Beside ani- 
 mals, portions of twigs and leaves also fall into the 
 pitchers and are more or less digested and absorbed 
 by the walls. Pitchers, in addition to manufactur- 
 ing food from the air by the aid of chlorophyl, are 
 seen to gain another supply from the bodies of the 
 entrapped animals and plants. 
 
 If convenient, the pouched leaves of the bladder- 
 wort should be examined in the same manner. This 
 plant floats near the surface of streams and ponds, 
 and the traps may be seen to contain a mass of 
 dark-colored contents which will prove to be the 
 remains of small aquatic animals. Some species of 
 
80 THE NATURE AND WORK OF PLANTS 
 
 this plant have traps large enough to receive young 
 fishes, and they kill large numbers of these animals 
 in the course of a season. 
 
 98. Food-building in the lower forms. — The leaf 
 is the most perfect organ for the display of chlo- 
 rophyl in such manner as to make the best use of 
 light, but in lower forms it is done in a simpler man- 
 ner. One generation of the mosses, ferns, and some 
 liverworts are furnished with organs like the leaves 
 of seed plants. In the other generation the body 
 is in the form of a thin plate, or solid mass of 
 cells, which lies flat on the surface of the ground. 
 The chlorophyl in such cases is carried in the upper 
 layers, where it may receive light. The seaweeds 
 exhibit a great variety of organs for this purpose. 
 Some of them are leaflike in general form, while 
 others are massive and carry chlorophyl in the 
 outer layers only; these plants also carry red and 
 blue coloring matter. The pond-scums, which float 
 on fresh water, consist of a chain of cylindrical 
 cells, and the green color is arranged in spiral bands, 
 like corkscrews, which run around just inside the 
 cell wall in all cells except the spores. In still 
 simpler forms the chlorophyl is diffused through 
 
THE LEAVES 81 
 
 the whole cell and not set apart in separate bodies, 
 as in the higher forms. Masses of pond-scum, with 
 bubbles of oxygen attached, are easily found in 
 almost any pond on a summer day. 
 
 99. Tlie leaf and loater. — All of the food taken 
 up by the roots is dissolved in one to ten thousand 
 times its weight of water, and is carried in this form 
 up through the stem and out into the leaves, where 
 it is used with the sugars to build up protoplasm or 
 make reserve foods. Some of this great amount of 
 water may be used also, but the greater proportion 
 is not needed further, and since there is no method 
 for its return to the roots it must be thrown off. 
 This must be done principally in the form of vapor. 
 The excretion of watery vapor constitutes the sec- 
 ond important function of the leaf. The process is 
 termed transpiration. 
 
 100. Course of the ivater in the leaf — The water 
 supply comes through the petiole, of course, and 
 when it reaches the lamina it divides into numerous 
 streams, each one of which follows a nerve or rib 
 and goes out into all of its branches. This may 
 be demonstrated if a leaf of the maple or poplar is 
 cut from the stem of a living tree, and the base of 
 
82 THE NATURE AND WORK OF PLANTS 
 
 the petiole inserted in a bottle of red ink or aniline 
 in water. Examine a day later. The color will 
 have marked out the conducting system of the leaf. 
 This will be found to distribute the liquid to the 
 remotest and smallest parts of the lamina. 
 
 101. Transpiration. — Clustered around the con- 
 ducting tubes are the soft, thin-walled mesojjhyl 
 cells, which draw water from the veins. The liquid 
 is constantly evaporated from the walls of these cells 
 into the air between them, and this connects with 
 the outer air by means of the thousands of minute 
 openings in the lower side of the leaf. The sun 
 shines on the upper side of the leaf, heating it and 
 the delicate cells underneath, and they constantly 
 evaporate water into the air spaces, and this air laden 
 with water pours out of the stomata and is replaced 
 by drier air from the outside. 
 
 102. Tlie vapor transp)ired. — That watery vapor 
 is thrown off by the leaf may be shown if the petiole 
 of a leaf is passed through a small hole in a large 
 piece of cardboard and immersed in a tumbler of 
 water. Put clay or wax around the petiole to pre- 
 vent any water vapor from coming up in this way 
 through the hole in the cardboard. Now invert a 
 
THE LEAVES 83 
 
 second tumbler over the blade. Examine a few 
 hours later. The vapor thrown off by the leaf will 
 have collected in the form of small drops on the 
 inside of the second tumbler. 
 
 103. Measurement of the amount of ivater tliroion 
 off by a plant. — Lay a piece of oiled cloth 18 inches 
 square on the table, and in the centre set a potted 
 geranium or tomato. Bring the edges of the cloth 
 up around the pot and tie closely around the base of 
 the stem. Water can now evaporate from the plant 
 only. Set on one pan of a grocer's scale and place 
 weights in the other pan until it balances. 
 
 If a scale is not to be had, suspend a wooden rod 
 by the middle and to each end tie a small bucket. 
 Place the plant in one and weights in the other. 
 Examine a few hours later. The plant will have 
 grown lighter. Remove weights from the opposite 
 end of the beam until the balance is restored. How 
 much weight has been taken out ? This represents 
 the amount of the water thrown off by the plant. 
 
 104. Sunlight increases transinration. — Repeat 
 this experiment in the sunlight and compare the 
 amount of water lost with that of the previous 
 experience. 
 
84 THE NATURE AND WORK OF PLANTS 
 
 105. Regulation and control of transpiration. — 
 The leaf is able to control the amount of water 
 given off by opening and closing the stomata. The 
 amount of moisture already in the air influences 
 the transpiration greatly, and as this amount varies 
 widely in different places tliere are a large number 
 of forms of leaves adapted to the different conditions. 
 The leaf may shield itself from the drying effects of 
 intense sunlight by heavy cuticles, coats of hair, or 
 wax, or by the upright positions described in § 93. 
 
 106. Wax or hloo7n as a means of prevention of 
 excessive loss of water. — Select some leaf which has 
 the surfaces covered with a whitish hloom (cabbage). 
 Kub the bloom from one and place it by the side of a 
 second which has been handled carefully in order not 
 to disturb the bloom. Which is the more wilted in 
 two or three hours ? The best results will be obtained 
 if the leaves are placed in the sunlight. 
 
 107. Size of leaves and dryness of the air. — Spe- 
 cies growing in dry air generally exhibit very small 
 leaves, while those living in wet places or where the 
 air is very damp develop large laminae. It is neces- 
 sary to have a stream of water constantly travelling 
 from the roots to the leaves, and plants living in 
 
THE LEAVES 85 
 
 very damp or rainy situations secure this stream by 
 building very large leaves. The banana is a com- 
 mon example, and many other tropical plants show 
 leaves several times as large. 
 
 108. Sleep movements. — If the position of the 
 leaflets of the bean or locust are noticed at sunset or 
 later, it will be seen that their blades are placed 
 nearly vertically. This position is supposed to be a 
 method of preventing the leaf from cooling so rapidly 
 as it would if held horizontal, and also from accumu- 
 lating a layer of dew which would hinder transpira- 
 tion. (See also § 93.) 
 
 109. Velvety surfaces. — If the leaves of some of 
 the species of begonias are examined, they will be 
 found to show an upper surface that is velvety to 
 the touch, and when examined with a hand lens 
 appear to have an immense number of small pro- 
 jections. This is due to the fact that the cells of the 
 upper side of the leaf are all extended in little cones. 
 The cones entrap the rays of sunlight as it were, and 
 refract them so that they warm the leaf and increase 
 the* transpiration over what it would be if the surface 
 were smooth. This device is also exhibited by the 
 petals of violets, pansies, and primulas. 
 
86 THE NATURE AND WORK OF PLANTS 
 
 110. Autumnal leaf fall. — The greater number 
 of the hardy or long-lived plants of the United States 
 are deciduous, or drop their leaves every year. This 
 casting of the leaves is one of the distinctive features 
 of the close of the growing season. It is popularly 
 supposed to be due to the action of cold, but this is 
 a mistake. The leaves of a large tree throw off as 
 much as a barrel of water in the course of a day, and 
 when the plant finds that it is losing water in the 
 dry August days faster than it can take it up from 
 the soil, it begins to get rid of the organs which use 
 most of it. 
 
 111. Separatory layer. — In order to be able to 
 cut off the leaf quickly and economically, a ring of 
 tissue is formed at the base of the stalk, w^hich 
 spreads the other tissues apart as it grows. After 
 this sejjarating layer is fully formed it is very brittle, 
 and the slightest breath of wind will split it apart 
 and allow the leaf to fall to the ground. In com- 
 pound leaves, such as the horse-chestnut, separatory 
 layers are formed at the base of each leaflet also, and 
 in some ivies a piece of the branch is cut off with the 
 leaf. 
 
 If a twig of maple with the attached leaf is taken 
 
THE LEAVES 87 
 
 from the tree in September, caiid a slicing cut is made 
 through the base of the petiole and the twig, the 
 separatory layer may then be seen with a magnify- 
 ing glass. Trees which usually shed their leaves 
 are sometimes seen to retain them during the winter. 
 This is usually due to the fact that the formation of 
 the separatory layer has been interrupted by cold or 
 drought. 
 
 112. The length of life of leaves. — The leaves 
 of the conifers and other evergreen trees may remain 
 in place on the branches two or three years, or even 
 longer. After a time, however, they become dam- 
 aged by the wind, and by insects or other agencies, 
 and are cast off. An evergreen tree is casting its 
 leaves almost continually, but as it loses but a few 
 at a time it is not noticeable. Quite a deep layer of 
 needles ma-y be found underneath almost any pine 
 tree. 
 
 113. Groivth of leaves. — The greatest variation is 
 shown in the method and rapidity of growth. All 
 parts of the organ do not grow with equal rapidity, 
 as may be seen by the following test : Mark off 
 intervals with India ink on the petioles and midribs 
 of leaves of sunflowers, narcissus, and any other con- 
 
88 THE NATURE AND WORK OF PLANTS 
 
 venient species. Measure from day to day and find 
 the total increase in length, and note the region of 
 greatest growth. In general, it will be found that 
 grasslike leaves grow at the base, while others 
 extend chiefly by the development of the terminal 
 portion. 
 
 114. Wilting. — If the leaf of any rapidly growing 
 plant is taken off and laid in the sun for an hour, 
 it may be seen that it becomes limp and is said to be 
 ivilted. Compare with a fresh leaf. It is quite flexi- 
 ble, and the soft tissues between the ribs appear to 
 be shrunken. Hold an end of the leaf in either hand 
 and pull until it breaks in two parts. Repeat with 
 a fresh leaf. The wilted leaf is as strong in this 
 way as the fresh one. It has not lost any of its 
 mechanical tissues, and its limpness must be due to 
 the loss of water. The cells of fresh leaves of the 
 plant are filled with water to such extent that 
 they are stretched and the walls are very firm, in 
 the same manner that the string of a bow is as rigid 
 as a bar of iron when the bow is prepared for use, 
 but quite limp and flexible when separate. 
 
 At noonday in midsummer and at other times the 
 leaves do not receive as much water as they evapo- 
 
THE LEAVES 89 
 
 rate, and as a consequence they wilt more or less. 
 The wiltmg is itself a protection against serious in- 
 jury, for in this condition the openings on the lower 
 surface of the leaf are closed, and the drooping posi- 
 tion assumed by the blade operates to diminish the 
 amount of water thrown off into the air. 
 
 115. Transplanting trees and herhs is attended 
 by wilting. — A plant usually develops a system of 
 roots with hairs capable of supplying the necessary 
 amount of moisture to the leaves, and when it is 
 lifted from the ground the process is attended with 
 more or less damage to the roots or hairs. When 
 the plant is set in a new position its absorbing pow- 
 ers are not so great as before, and if it is allowed to 
 retain all of its leaves, it will throw olf more water 
 than it receives, and wilting will result. To avoid 
 this the branches are trimmed in such manner as to 
 reduce the evaporating surface to the proper propor- 
 tion to the roots. One may see nurserymen putting 
 out trees, the tops of which have been trimmed to 
 bare poles. 
 
 116. Freezing or frosting. — An observation of 
 the plants growing in the open air after the first 
 frost of autumn will show that the leaves of some 
 
90 THE NATURE AND WORK OF PLANTS 
 
 species are quite blackened and shrivelled, while 
 others still appear bright and green and remain so 
 until the actual approach of winter and many frosts 
 have been endured. This leads at once to the con- 
 clusion that separate species have different powers of 
 resistance to cold. 
 
 It is seen at once that a temperature sufficient to 
 freeze water does not kill all species. Then again 
 some species, such as the melons, coleus, tobacco, and 
 tropical plants are killed by temperatures of two 
 degrees above the freezing point. Apple leaves are 
 killed by a temperature of two to six degrees below 
 the freezing point, cabbage five to seventeen be- 
 low, peaches two or three below, tomatoes one below, 
 wheat one below, strawberries two to four below, 
 while the grasses of the Arctic regions endure temper- 
 atures of eighty and ninety below the freezing point. 
 
 The water in some species may be frozen without 
 damage to the protoplasm, but if the frozen speci- 
 mens are brought into a warm room and thawed 
 quickly, the shock of the sudden change will kill 
 them. It is for this reason that frozen specimens 
 may be sometimes thawed without damage in water. 
 The use of the water also prevents the specimen 
 from drying out. 
 
THE LEAVES 91 
 
 117. The air is colder on a frosty night near the 
 ground than it is a few feet above it. — If one ther- 
 mometer is hung near the surface of the ground on 
 a quiet night in mid autumn, and another ten to 
 twenty-five feet higher in the branches of a tree, 
 it will be found that it may be five to ten degrees 
 colder near the ground than it is in the tree tops. 
 This is due to the fact that the soil cools very 
 rapidly, and the layer of air resting on it is also 
 cooled, while the upper air is comparatively warm. 
 On account of this fact the leaves and buds on the 
 lower branches of a tree may be frosted, while those 
 on the upper part are untouched. The low-growing 
 shrubs and herbs will be frosted before the taller 
 trees. If, however, a great movement of wind from 
 the northward covers the country with cold air, it 
 will result in a general freeze which affects all alike. 
 The farmer and the fruit raiser prevent damage to 
 their crops from frosts by covering the plants with a 
 shield which will prevent the loss of heat by the 
 ground and by the plants, by building fires to heat 
 up the layer of cold air, or by making smudge fires 
 which add heat, smoke, and moisture to the air, 
 making a fog blanket that prevents the loss of heat 
 as effectually as a covering of cloth might do it. 
 
92 THE NATURE AND WORK OF PLANTS 
 
 None of these devices may protect against freezing 
 in general cold weather. 
 
 118. Drainage of cold air. — The layer of cold 
 air on the surface of the soil is heavier than the 
 warm air above it, and in rough or broken country 
 this heavier air flows down hill as water would, 
 accumulating in the valleys, w^hich thus become very 
 much colder than the hill-tops around them. The 
 temperature of the valleys is often ten to twenty 
 degrees lower than that of the hills near by. As a 
 consequence of this fact, vineyards, orchards, and 
 gardens, in which delicate varieties are cultivated, 
 are planted on ridges and hills in preference to 
 low-lying valleys. 
 
VI. STEMS 
 
 119. The nature of stems. — The stem is the 
 main axis, or central member of the body of the 
 plant. From its lower end the roots arise and pene- 
 trate the soil, while leaves and reproductive organs 
 are borne on its upper part. Stems are often de- 
 scribed as springing from roots, when they grow 
 from underground stems. This is a mistake, except 
 in a very few instances in which roots are capable of 
 giving rise to stems. 
 
 It is necessary that the roots should be buried in 
 the soil for the purpose of absorbing food, and that 
 the leaves should be held up in the sunlight to 
 enable them to form food ; also that the reproduc- 
 tive organs should be held in . a position that will 
 enable them to perpetuate the species. This means 
 that the roots on one hand and the leaves and flow- 
 ers on the other may be separated by some distance. 
 The stem is the connecting member, and its bulk and 
 length will vary with the habits and needs of the 
 separate species. 
 
94 THE NATURE AND WOBK OF PLANTS 
 
 120. Stems are made up of sections, or internodes. 
 
 — If the stem of a mint or of the corn is examined, 
 it will be found that it exhibits a number of 
 "joints," indicated by external ridges which divide 
 it into a number of sections. Take two sections of 
 the stem not adjoining, and compare them. No dif- 
 ference will be found except in the matter of size 
 and age. The arrangement of the tissues is identi- 
 cal. Repetition of this test will show that a stem is 
 made up of a number of sections of the same struc- 
 ture. This characteristic is one which is not found 
 in any other member of the plant. 
 
 121. Branches arise at the nodes or joints only. 
 
 — The branches of roots were seen to arise at 
 any point on 'the main root. Leaves, branches, 
 and flowers are seen to be given off at the 
 nodes only of stems. Roots emerge from the ex- 
 treme lower end of the stem, or they may arise 
 from the lower nodes, as in the case of the stilt or 
 prop roots of the corn, or from any part of the stem 
 in climbing species. 
 
 122. Relation of the leaves and branches. — It 
 may be seen that buds or branches arise from the 
 stem immediately above the point at which a petiole 
 
STEMS 95 
 
 is attached, that is, in the axil of the leaf. While 
 this is generally the case, yet many species give off 
 branches just below the leaf. Wherever a branch is 
 seen on a stem, one may be certain that it arose 
 originally just above or below a leaf. The leaf has 
 fallen off, and the branch has continued to grow and 
 enlarge until all trace of the leaf is lost. 
 
 123. Leaf traces. — When the leaf falls from 
 the stem its petiole is cut off cleanly by means of 
 the separatory layer described in a previous para- 
 graph. The scar is noticeable for some time, and 
 may be seen very plainly on the twigs of the maple, 
 oak, or chestnut, or on the vine of the grape. 
 
 124. Relation of leaves and floivers. — Flower 
 stalks are also seen to arise from the axils of leaves. 
 A single flower on its own stalk may arise from the 
 axil of the leaf without changing the character or 
 the size of the latter in any way. When a branch 
 bears a great number of flowers closely crowded 
 together, like the lobelia, the mints, mullein, and 
 larkspur, the leaves at the basis of the numerous 
 flower stalks are much smaller than those on other 
 parts of the stem, and are scarcely more than little 
 wedges of green tissue which are termed bracts. 
 
96 THE NATURE AND WORK OF PLANTS 
 
 125. Structure of stems. — If a small branch of 
 the elm, beech, maple, or chestnut is cut off and then 
 a portion of the branch is split lengthwise, it may be 
 seen that a hard covering of bark encloses the whole. 
 Immediately inside this is a layer of soft tissue of 
 material easily crushed and full of water. This 
 material is living while the bark was chiefly made up 
 of dead tissues. Small extensions of the living tissue 
 penetrate the wood which' occupies the greater part 
 of the volume of the branch. In the centre is to be 
 seen a small amount of soft pith, which may easily be 
 cut or torn, and is generally made up of dead cells in 
 older branches. The branch is thus seen to be com- 
 posed of living and dead cells, and the dead tissue 
 greatly exceeds the living in bulk. 
 
 126. Uses of stems. — The purpose of the stem 
 is twofold : to hold up the leaves and flowers, and 
 to conduct water and food between the leaves and 
 roots. The method by which these functions are 
 carried out may be best understood after a study 
 of the scheme in which the tissues are arranged in 
 the stem. This has been seen roughly in the branch 
 of the tree examined, but it will be necessary to see 
 the manner in which the different parts of the living 
 
STEMS 97 
 
 and dead tissues are disposed with regard to each 
 other. 
 
 127. Methods hy ivhich firmness is secured. — If 
 the stem is to hold the leaves and flowers aloft, 
 it must secure a certain amount of rigidity in its 
 own body. It does this by two methods, which 
 may be illustrated as follows : Cut off a fresh branch 
 from a woody tree, and also the stem of a tomato or 
 potato, ajad lay in the hot sun for two hours. Take 
 a second fresh branch from the tree and bend or 
 break it across the knee. Bend or break the one 
 which has lain in the sun in the same manner. Has 
 the latter lost any of its rigidity or firmness ? Is it 
 more easily bent ? Repeat with other stems. What 
 is the result ? It will doubtless be found that the 
 herbaceous stem has lost its firmness and that it is 
 wilted and may be very easily bent double, while the 
 ivoody stem is practically unchanged. Both stems 
 lost water in the sun. This did not affect the woody 
 stem, but did the other. It seems fair to conclude 
 that the presence of water is necessary for the firm- 
 ness of herbaceous stems, and it is not for the woody 
 stems. If the experiment is carried farther, it will 
 be found that dead and thoroughly dried stems 
 
98 THE NATUEE AND WORK OF PLANTS 
 
 are more rigid than the living members. This is 
 due to the fact that even the soft living tissues 
 become hard when dead and dry. 
 
 Stems secure firmness by the presence of hard 
 mechanical tissues and by filling soft tissues full of 
 water under pressure, as in leaves. 
 
 128. Arrangement of hard or dead cells to secure 
 firmness of stems. — The dead cells of stems are 
 arranged in the form of strands or girders after the 
 principles used by an engineer or architect in con- 
 structing a tower or tall building. The architect 
 uses wood, brick, cement, and metal as material 
 from which to construct the tower. The plant uses 
 loood, hast, which resembles cable or wire rope in its 
 properties and is as strong as wrought-iron, col- 
 lenchyma, which is elastic, and also soft ^:>z7/i cells. 
 The properties of wood are too well known to need 
 discussion. Bast cells make up the fibres which are 
 taken from the flax plant and used by man, and col- 
 lenchyma forms the sharp angles of the stems of the 
 mints and is very much like cartilage or rubber. The 
 plant has thus rigid beams, flexible cables, and soft 
 spongelike filling or cement for its building mate- 
 rials, and the towers it constructs are greater in 
 
STEMS 99 
 
 height in proportion to tliickness, and show greater 
 strength and efficiency, than those built by man. 
 
 129. Arrangement of mechanical tissues iti a 
 stem of a grass. — Secure an uninjured cornstalk. 
 Take out a single internode, or the part between 
 two joints, and dissect it. Note the hard plates 
 which extend entirely through the stem at the nodes. 
 The outer layer is in the form of a cylinder and is 
 hard and rigid. Cut in two parts lengthwise. The 
 interior is filled with the soft pith. In this pith 
 are great numbers of strands and fibres which run 
 from the plate at one end to the other. Now split 
 the entire piece into small strips, and without injur- 
 ing any of the separate parts tie them together in 
 a bundle. Lay the bundle on a table with half of 
 its length projecting over the edge. Weight down 
 the end on the table. Now tie weights to the other 
 end and determine the amount necessary to break 
 the bundle of building material. Repeat the opera- 
 tion with a section of the stem which has not been 
 dissected. It will doubtless be seen that the mate- 
 rials themselves are not very strong, but when fitted 
 together in proper form they make an extremely 
 rigid stem. 
 
100 THE NATURE AND WORK OF PLANTS 
 
 The cornstalk is seen to be a cylindrical tower, 
 many storeys in height. Each storey is filled with 
 the cementing pith, and numerous braces run from 
 the ceiling to the floor of each in a method that 
 could not be improved by the best engineer. 
 
 130. Mechanical tissues in a sunflower stem. — 
 Repeat the above experiment with the stem of the 
 sunflower. Cut across a young stem and note the 
 position of the building elements. A few strands of 
 wood will be found arranged in a circle, and on the 
 outer side of each bundle of wood is a bundle of 
 bast. The centre of the stem is filled with pith. 
 
 131. Mechanical tissues in a carnation stem. — 
 Repeat the tests of strength with a carnation stem. 
 Cut a stem length- and cross-wise and note the 
 manner in which the material is arranged. The 
 bast will be found to form a circle, and immediately 
 attached to the inside of this circle is a second circle 
 of wood. The centre is filled with pith. This stem 
 is then like a tower made of two strong tubes 
 fastened together, and the centre is filled with the 
 cementing pith, which is also living and which be- 
 comes firm and bracing by the absorption of water. 
 Examine the stem of a mint in the same manner. 
 
STEMS ' 101 
 
 132. Arrangement of rtieclianical tissues in a 
 petiole. — The types of stems described above stand 
 erect and support the weight of the leaves like a 
 pillar, and the bending force of the wind like a 
 tower. The petioles of leaves generally hold the 
 blade in a horizontal position, and the weight acts 
 always to bend the petiole in one direction, down- 
 ward. To meet this strain it is necessary to have 
 the building material arranged in a half circle, as 
 may be seen if the leaf of the maple or chestnut is 
 examined. 
 
 133. TJie firmness of plants that "become limp 
 when dried. — Select a young stem of any plant which 
 would become limp if you laid it in the sun. The 
 tips of elder stems in April or May will offer splendid 
 material. Cut away from opposite sides of the stem 
 until only a thin strip remains, which includes the 
 central part of the stem. Now divide this exactly 
 down the middle with a sharp knife. This will 
 make two sheets of material, each of which is com- 
 posed of a strip of living pith full of water under 
 pressure, and the wood which will bend but not 
 stretch. After a few minutes place the two strips 
 together in their original position. What changes 
 
102 THE NATURE AND WORK OF PLANTS 
 
 of form have they undergone ? Cut the stalks of 
 the calla lily or rhubarb into strips, and note be- 
 havior. 
 
 134. Stems as conducting organs. — The position 
 of the stem between the leaves where sugars and 
 other substances are manufactured and the roots 
 where water and mineral salts are taken up makes 
 it necessary for it to conduct the products of the 
 leaf downward, and the materials taken up by the 
 leaf upward. There is a stream of water upward 
 and a stream of food material downward, but the 
 two are not connected, and there is nothing like a 
 circulation of the sap. 
 
 135. Upward path of sajJ. — Cut off a stem of 
 the tomato or touch-me-not with a number of sound 
 leaves attached, and thrust the lower end of the 
 stem into a bottle of red ink or a tumbler of water 
 colored with aniline dye. After four or five hours 
 remove and dissect the stem. What portions are 
 colored ? This will show through what tissues the 
 liquid has passed. It is to be seen that the dead 
 wood cells also serve as conduits for water in addi- 
 tion to their function of making the stem rigid. 
 
STEMS 103 
 
 136. Fath of sap in large trees. — Each year a 
 new layer of wood is added to the trunk of a tree, 
 thus increasing its thickness by the small part of an 
 inch. If the previous experiment might be repeated 
 with a large tree, it would be found that only the 
 outer layers of wood in the trunk would be colored, 
 showing that it is through these only that the sap 
 ascends. 
 
 137. Girdling. — An interesting fact in this con- 
 nection is the behavior of a tree when girdled. 
 •Girdling is usually done by removing the bark, 
 the living layer, and some of the outer wood of the 
 trunk, and is done for the purpose of killing the 
 tree. In most species the removal of the outer 
 layer of wood cuts off the conduits which carry the 
 water to the leaves, and if it is done in the spring, 
 the tree generally dies the following summer. Some 
 are able to send water up through the inner layers, 
 and not only live that year but the following year 
 also. A few instances have been found in which the 
 tree has survived the operation many years. 
 
 138. Doivmvard path of material from the leaf. — 
 Trees which live through one summer but die at the 
 beginning of the next, are injured by starvation of 
 
104 THE NATURE AND WORK OF PLANTS 
 
 the roots. These organs are constantly receiving 
 material from the leaves, but have a surplus on hand 
 almost all of the time, and some is also to be found 
 in the lower part of the stem. During the first year 
 this is sufficient for their nourishment, but it is gen- 
 erally exhausted before the beginning of the next 
 season. This material passes down very slowly 
 through the layer of living tissue immediately under- 
 neath the bark, and its flow is interrupted in any 
 girdling operation. If the tree lives several years 
 after girdling, it may be supposed that its roots have 
 formed partnership with fungi in such manner that 
 it receives its food from them (see § 52). As a mat- 
 ter of fact the stumps of many of the coniferous 
 trees are known to live for long periods, perhaps a 
 decade, by means of food obtained in this manner. 
 
 Girdling of branches is used as a method of 
 increasing the size and quality of fruit borne on 
 them. 
 
 139. Forces ivhich carry the sap upioard through 
 the stem. — Information upon the forces which pump 
 water up to the top of tall trees is very incomplete. 
 It is quite certain that it needs as much power to 
 carry water to the top of a tree a hundred feet high 
 
STEMS 105 
 
 as it does to send it up through an iron pipe to the 
 same distance. As a matter of fact it takes more 
 force to carry it up in the tree because it must pass 
 through such very small vessels. While the whole 
 process may not be fully understood, yet some fea- 
 tures of it may be illustrated in the following 
 paragraphs. 
 
 140. Boot or Needing pressure. — If the stump 
 of a tree which has been cut down in the spring is 
 examined it will be seen that the sap is oozing from 
 the cut surface in great volume, and if a cup is 
 placed under the cut end of a grapevine at this 
 season the amount of liquid thrown out may be 
 measured. This bleeding is due to a pressure exerted 
 by the living cells of the stem and roots, and it is 
 sufficient to force water to the tops of small plants 
 like the sunflower in the temperate zone and in trees 
 in the tropics, but in the United States it could not 
 send sap to the leaves of large trees. Then, again, 
 root pressure is strong only in early spring. 
 
 141. The floiv of sap of the sugar maple. — Not 
 all flow of sap is due to bleeding pressure. Sugar 
 maples are tapped to obtain the sweet sap at a time 
 in the spring when the ground is still frozen. The 
 
106 THE NATURE AND WORK OF PLANTS 
 
 flow is due in part to the effect of the sun's rays 
 upon the trunk, heating and expanding the liquids 
 and gases in it, and driving the sap out the auger 
 hole in this way. After the ground thaws out the 
 sap ceases to flow in quantity. 
 
 The sugar obtained from the sap has been stored 
 up in the pith cells in the rays of the wood during 
 the winter. 
 
 142. JDeiv. — The sparkling gems of dew which 
 make a lawn so beautiful of a summer morning are 
 not usually formed from the air, but are drops of 
 water which have been forced up through the leaves 
 by the root pressure. During the warm and sunny 
 part of the day the water is thrown off by the leaf 
 as fast as it may be received from the roots, but at 
 night the air is cool and moist, and it is not able to 
 do so. As a consequence, the liquid is forced up until 
 it fills the spaces in the leaf and finally oozes out 
 through slits in the epidermis. Of course dew may 
 be formed by the condensation of moisture from the 
 atmosphere, but that on grass usually comes up from 
 the roots. 
 
 143. Hoiv to cause a plant to form dew at any 
 time. — By putting a plant in the same conditions as 
 
STEMS 107 
 
 the grass at night, it can be induced to form dew. 
 To do this, set a large glass dish over a vigorous plant 
 of geranium or begonia in such manner that it will 
 be tightly enclosed. If it remains in this position 
 for a few hours, the air inside the vessel becomes 
 saturated with watery vapor, and the leaves are 
 unable to throw off any more. The continued sup- 
 ply from the roots is forced out through the leaf at 
 the edges in the form of large drops. These become 
 so large that they fall off and others collect in the 
 same place, so that moist spots will be formed in the 
 soil where they fall. This demonstration will be 
 most successful if the plant is allowed to remain 
 covered over night. 
 
 144. Lifting poiver of leaves and tranches. — It 
 has been shown in a previous experiment (§ 135) 
 that a leafy stem will pull colored fluid upward 
 in the stem, and if proper apparatus were at hand 
 it could be proved that it does so with great force. 
 Both the lifting power of the leaves, and the pump- 
 ing power of the roots seem insufficient to send up 
 the necessary amount of water to the leaves, for it 
 will be remembered that a poplar tree uses a bar- 
 rel or more of water every day during the summer, 
 
108 THE NATURE AND WORK OF PLANTS 
 
 and smaller quantities at other times. There is 
 still much to be found out about the ascent of 
 sap. 
 
 145. Growth of stems. — The manner in which 
 stems grow and increase in size bears a close rela- 
 tion to the arrangement of the mechanical elements. 
 The arrangement of the living tissues is different 
 in the various types, of course. From the many 
 forms of the stem it will be most profitable to select 
 a tree and the cornstalk for study of this feature. 
 
 146. Action of einhnjonk tissue of a tree. — The 
 living cells of a tree which constantly divide, form- 
 ing others which pass into dead tissue, lie immedi- 
 ately underneath the bark and completely sheathe 
 the trunk, forming a small cone of delicate cells at 
 the tips of the stems and branches and in the buds. 
 Dead cells are constantly being formed on the inner 
 side of this layer and added to the wood. The 
 cells formed in any one season are distinguishable 
 from those of the last season and constitute an 
 annual ring, though sometimes two rings may be 
 formed in one summer. At the same time dead 
 cells are being added to the bark on the outer 
 side of the living tissue. The living- cells at the 
 
STEMS 109 
 
 tip divide and push forward, leaving dead cells 
 behind them. 
 
 147. Growth in length and diameter. — Dead cells 
 do not increase in size, of course, so that the trunk 
 of a tree does not elongate except at the tips of 
 the stems and branches. Thus a branch on the 
 trunk will always remain the same distance from 
 the roots. Its distance from the ground might be 
 increased by the washing away of the soil below it. 
 This may be demonstrated if a nail is driven in 
 the trunk of a tree near the surface of the soil, 
 and a second as high above it as may be conven- 
 ient. Measure the distance between them quite 
 exactly, and then repeat a few months or a year 
 later. 
 
 148. Measurement of growth in length. — Mark 
 the stem of some rapidly growing plant, such as 
 bean or sunflower, with India-ink at intervals of 
 half an inch. Measure these intervals on three or 
 more successive days. Do all of them increase ? 
 What part of the stem increases in length with 
 greatest rapidity? 
 
 149. Measurement of groivth in diameter. — The 
 increase in diameter of a plant is not so easily 
 
110 THE NATURE AND WORK OF PLANTS 
 
 obtained. Perhaps the best method is to drive two 
 nails into the opposite sides of the trunk of a vigor- 
 ous young poplar in early spring, and then find 
 the exact circumference of the tree an inch above 
 these nails with a tape measure. Repeat the opera- 
 tion of measurement about the first of September. 
 
 150. The hark. — The behavior of bark should 
 be studied in connection with growth in thick- 
 ness. The yoimg poplar and many other young 
 trees are seen to have a smooth bark, while older 
 specimens have a very rough or even a shaggy 
 covering. The cells which compose the bark of the 
 younger trees are alive, and divide and grow in such 
 manner that they keep pace with the increase of 
 the trunk. After the tree reaches a certain age 
 the bark does this no longer. Any increase in the 
 trunk then results in the splitting of the bark, 
 leaving the edges exposed. A new layer of bark 
 is formed which is applied to the inside of this slit 
 like a patch. This process is repeated every year, 
 an,d as a consequence some trees, such as the oaks, 
 hickories, and poplars, have a very rough or shaggy 
 bark. The sycamore is an example of a tree which 
 casts away the old layer of bark each year and 
 
STE3f8 111 
 
 presents a new coat of smooth, clean, greenish 
 white bark to the weather. The bark serves to 
 protect the layer of living tissue from damage by 
 the climate, or by animals, or from the falling 
 trunks or branches of other trees. On the other 
 hand, the numerous crevices afford lodgment and 
 refuge for the spores of parasitic fungi which ger- 
 minate and injure the tree, and also harbors insects 
 and other animals which work injury in many 
 ways. 
 
 151. Groivth of a corn stem. — Select a young 
 and rapidly growing corn stem and mark off three 
 or four of the terminal internodes into half-inch 
 intervals by means of India-ink. Measure these 
 from day to day for a week. What places show 
 elongation ? 
 
 Trees are generally larger at the bases, but in the 
 corn plant and in the palms and their relatives the 
 basal part of the stem will be found to be smaller 
 than parts of the stem above it. This is due to 
 the fact that such stems soon reach their full growth 
 in thickness at the base, and the later portions 
 formed may receive more food and attain a greater 
 thickness. 
 
112 THE NATURE AND WORK OF PLANTS 
 
 152. Noddiyig or circular movements due to un- 
 equal growth. — Select a vigorous specimen of the 
 hop, bean, or morning-glory, and tie all of it to an 
 upright stake except the tip of the stem a foot in 
 length. Now set a second thin stake in the ground 
 so that its top is just below the tip of the stem. 
 Note the position of the tip an hour later. If it has 
 moved, set up another stake. Repeat this process 
 until the tip has moved around in a complete circle. 
 What was the direction of the movement? What 
 length of time was necessary to complete the circle ? 
 This circular movement of the tip is due to the 
 fact that one side of the stem grows faster than 
 the other sides for a short time, then it slows down 
 and a region next to it grows most rapidly, and 
 so on around the stem. This results in tilting 
 the tip toward every point of the compass in suc- 
 cession. 
 
 A nodding movement, due to the alternate growth 
 of two sides of a flattened organ, may be seen if the 
 growing leaves of narcissus are observed in this 
 manner. 
 
 153. Length of life. — The length of time a 
 single specimen of a plant may live varies enor- 
 
STEMS 113 
 
 monsly. Thus in some of the lower forms an indi- 
 vidual may be grown from a spore, attain maturity, 
 give rise to new individuals, and die in a few hours 
 or even in a few minutes. The spores of these same 
 species may be capable of living many years in a 
 resting condition, however. Among the seed plants 
 the cycle of life varies from sixty or seventy days in 
 some of the herbs to three thousand years in certain 
 kinds of trees. It is estimated that some trees can 
 live to twice this age, though the lack of records 
 does not allow this to be verified. The estimation of 
 the age of a tree by counting the annual rings is 
 subject to error, since the number of these rings may 
 be nearly twice the age of the tree in years. All 
 seed plants may be roughly classed as annuals, bien- 
 nials, and perennials. 
 
 154. Annuals. — Annuals are those which live 
 but one season. The seeds germinate, and a system 
 of roots, a stem, and branches are formed, and seeds 
 are matured in a period which varies from two to 
 four months. Species of this character may gener- 
 ally be distinguished by the character of the stem 
 and root system. Annuals live through the winter 
 in the form of seeds only. Examine twenty species 
 
114 THE NATURE AND WORK OF PLANTS 
 
 and select the annuals. What cultivated plants are 
 grown as annuals? 
 
 155. Biennials. — A second group of species 
 germinate the seeds, form a stem with a rosette of 
 leaves and an extensive root system in one year, and 
 then develop the flower-bearing branches, flowers, 
 and seeds the second season. Some of the thistles 
 and the common mullein belong to this class. 
 
 156. Perennials. — Quite a large number of spe- 
 cies germinate the seeds and form stems the first 
 year, then rest during the winter, and continue 
 growth during the next season and for many succes- 
 sive seasons. In trees and similar forms the entire 
 stem remains alive, and consequently it increases in 
 bulk each year, attaining an enormous size. The 
 giant trees of California have attained a trunk about 
 four hundred and fifty feet high, and thirty feet in 
 diameter. These are by no means the tallest trees 
 in the world. 
 
 Another class of perennials have a stem which lies 
 just underneath the surface of the soil, sending 
 branches up into the air each year. These die down 
 on the approach of winter. Meanwhile the under- 
 ground stem grows at the tip, and would increase its 
 
STEMS 115 
 
 length, but the other end of the stem, which is also 
 the oldest, constantly dies away so that the plant 
 does not greatly increase in size. The great size of 
 the bulky perennials subjects them to many dangers 
 which the underground stem does not incur, and 
 it would be difficult to set a limit to the age which 
 the latter may reach. The ravages of animals, ex- 
 tremes of heat and cold, washing away of the soil by 
 rains, or the growth of more vigorous species around 
 them, would tend to set a limit to the age which they 
 may attain. 
 
 157. Changes in the length of life of a species. — 
 The length of life of any species is an adaptation 
 to the conditions under which it lives. Changes 
 may be brought about when the plant is introduced 
 into a new habitat. Thus the ordinary tomato is 
 an annual, as it is grown in gardens ; yet if it is 
 cultivated in a greenhouse and sheltered from the 
 weather, it may live two or three times as long. 
 Bringing a species into a severer climate may have 
 the effect of reducing a perennial or a biennial to 
 an annual. 
 
 158. Buds. — Immediately underneath the epider- 
 mis, or bark, lies the layer of living tissue which is 
 
116 THE NATURE AND WORK OF PLANTS 
 
 capable of great multiplication of cells and growth. 
 At certain points this tissue has acquired the power 
 of forming new branches, flowers, and leaves, hence 
 it is called embryonic tissue. These specialized 
 masses of cells are generally in the form of minute 
 outgrowths, and are located at the tips of the stem 
 and its branches as well as in the axils of the 
 leaves. This tissue is most delicate and easily in- 
 jured, and is generally protected by coverings of 
 leaves or bracts. The growing points or masses of 
 embryonic cells and their coverings form buds. 
 
 159. Naked hiids. — In sJDecies growing in tropi- 
 cal and mild climates the buds are only slightly 
 shielded by the young leaves near the tip of the 
 stem, and no special coverings are developed. Such 
 an arrangement is called a naked hud, and an ex- 
 ample may be seen m the cultivated geranium or 
 pelargonium. 
 
 160. Scaly huds. — Plants which grow in cold 
 or dry climates generally adopt some method of 
 protecting the growing points from damage. The 
 most common device is a number of wrappings of 
 brownish scales, which are in reality a special form 
 of leaves which are used for protection instead of 
 
STEMS 117 
 
 food formation. The scales are fitted around the 
 growing point so closely as to make a compact 
 conical mass that is very firm. In addition the 
 scales are often furnished with a coat of hairs or 
 a layer of balsam or varnish which makes them 
 absolutely waterproof. These scales do not keep 
 the growing plant warmer than the surrounding 
 air, but they protect it from damage by ice or frost, 
 and also prevent drying out. 
 
 161. Buds of the apple. — Secure some winter 
 buds of the apple by cutting off twigs two feet in 
 length two weeks before the subject is to be studied, 
 and placing the cut ends of the stems in a dish of 
 water in a warm room. Now carefully dissect some 
 buds freshly procured from the tree. Take off 
 the scales, one at a time, noting the manner in 
 which they are fitted to each other. The central 
 mass of the bud should contain the young leaves 
 and perhaps flowers. Tear apart and note shape 
 and size. Later examine the opening buds. What 
 changes have taken place which would cause the 
 scales to come apart? and what changes have 
 occurred in the shape and size of the leaves and 
 flowers? Note all these points by sketches. 
 
118 THE NATURE AND WORK OF PLANTS 
 
 162. Buds of elder, maple, or elm. — Sketch a 
 twig of one of these plants, showing the leaf scars 
 and the position and size of the buds. Treat as 
 above. 
 
 163. Sleejmig huds. — It is to be seen that a 
 bud is simply a young branch, and, furthermore, 
 that all the branches of the plant are developed in 
 this manner. It is important, therefore, that the 
 plant should be furnished with an ample supply of 
 them, so that the destruction of a few need not 
 deprive it entirely of the power of making new 
 branches. There is one or perhaps more of these 
 growing points at the base of every leaf. Only a 
 small proportion of them develop in any year, the 
 remainder lying quiescent, and may continue to do 
 so for years, being known as sleejnng huds. Many 
 of these structures may be found on the lower 
 parts of the stems of young trees. 
 
 164. The aioakening of sleejmig huds. — If the 
 top of a tree is cut off, some of the sleeping 
 buds remaining on the upper part of the stem 
 start into life, developing branches, and giving the 
 plant a low, compact appearance. In the pruning 
 
STEMS 119 
 
 of fruit trees the sleeping buds are often called 
 into action. 
 
 165. Winter huds of aquatic ^9/a?i^s. — In one 
 class of land plants the upper branches of the stem 
 have been seen to die down, leaving only the basal 
 portion of the stem with its buds to live through the 
 winter. Exactly the reverse action takes place in 
 some aquatic plants which root in the bottom of 
 streams or lakes, or which float on the surface. If 
 a visit is made to a lake or pond about the time that 
 the trees have lost all their leaves, this curious bud 
 formation may be found. The stems of the pond- 
 weeds, stonewort, bladderwort, and others will be 
 seen to have taken on a brownish color except at 
 the tips. Here the stem is still alive, and a large 
 number of leaves of a dark green color overlap each 
 other closely, forming an egg-shaped mucilaginous 
 mass. Break off some of these buds and find if 
 they will float alone. These buds are sometimes 
 termed hibernacula. Preserve your notes upon the 
 subject and visit the same pond in the following 
 spring as soon as the ice has melted. A great num- 
 ber of the winter buds may be seen floating near 
 the surface of the water. Examine, and note their 
 
120 TUE NATURE AND WORK OF PLANTS 
 
 identity with the kinds seen the previous autumn. 
 They are plentifully furnished with red and purple 
 coloring matter as a result of the low temperatures 
 under which they have lived. 
 
 166. Behavior of the hibernacula. — The hiber- 
 nacula sink to the bottom of the water in the 
 autumn, and thus escape the action of the ice. This 
 is also done by the minute pond-scums and other 
 forms which are seen to float on the surface in great 
 quantity in the summer. When the ice disappears 
 in the spring and the sun's rays begin to warm the 
 water, several bubbles of gas are formed in them, 
 which helps float them to the surface. Now the 
 bud begins to unfold, and the tip of the enclosed 
 stem to grow in length, while long roots grow out 
 from the basal end. Perhaps it finds lodgment in 
 the mud in shallow water, and the new season's work 
 is begun. 
 
 All water plants do not form such buds. Water 
 lilies have great stems lying imbedded in the mud at 
 the bottom of the pond, and these send up leaf and 
 flower stalks which reach the surface and perform 
 their function during the summer, dying down on 
 the approach of cold weather. 
 
STEMS 121 
 
 167. Bulhs. — Split an onion, hyacintli bulb, or 
 any similar structure. It will be seen tliat it is 
 simply a great bud, with the scales which surround 
 the growing point very much thickened and loaded 
 with food. The centre of the bud is a short, thick- 
 ened stem. Bulhs are buds that are usually detached 
 from the plant as soon as they are formed, and when 
 they grow, they as well as hibernacula make a new 
 individual and therefore serve to reproduce the 
 species (§ 183). 
 
 168. Corms. — An interesting method by which 
 delicate plants endure a severe winter consists in the 
 formation of short, thick, upright stems, like those 
 of the calla or the jack-in-the-pulpit. Examples of 
 the latter may be found in almost any woods. On 
 the upper side of such short squat stems may be 
 found a large conical bud, covered by a few large 
 scales, wrapped tightly around the central mass. 
 Cut open such a bud; the young leaves and flowers 
 for the next season will be found perfectly formed, 
 except in size, as early as June or July, ten months 
 before they are to be called into action. 
 
 169. Forcing, or inducing an earlier growth. — If 
 these corms are taken from the soil in the autumn 
 
122 TUE NATURE AND WOEK OF PLANTS 
 
 and allowed to remain out of doors in the cold until 
 the first of December, then put in a cellar for a 
 month or two, they may then be potted and will 
 begin to grow. Note the behavior of the bud cover- 
 ing. It does not burst open immediately, but elon- 
 gates until it reaches the surface of the soil, and then 
 only does it open and expose the young leaves. Set 
 the pot with the growing bud in a dark room, or 
 cover it with a pile of moss. The bud will con- 
 tinue to elongate until it reaches the light, or it has 
 attained a length of seven or eight inches, which 
 seems to be its limit of growth. Its purpose is to 
 bring the leaves above the surface of the ground, and 
 it does not open until it is struck by the light, which 
 is usually a signal that this has been accomplished. 
 
 170. So7ne protective devices of the shoot. — 
 Leaves and stems are subject to destruction by 
 animals which use them for food, and a large 
 number of species are furnished with structures 
 which hinder or prevent attack by the animal. The 
 most common means of protection consists in poison- 
 ous or hitter substances in the tissues, spines, prickles, 
 hristles, thorns, and stinging hairs. 
 
 The acrid burning sensation which follows tasting 
 
STEMS 123 
 
 jcack-in-the-pulpit preserves it from the ravages of 
 grazing animals, and the well-known qualities of the 
 poison ivies serve a similar purpose. The active 
 substance in the latter case is an oil secreted by the 
 leaves and stems, making even proximity dangerous 
 to the animal. 
 
 The prickles of roses and other shrubs are exam- 
 ples of Aveapons coming from the epidermis of the 
 stems, and which may come away in the body of 
 the animal which comes into contact with the stems. 
 The thorns of many species, including the well- 
 known honey locust (Gleditschia), are branches which 
 have altered their method of growth in such manner 
 that they are very effective weapons for defence. 
 
 The edges of the leaves of some grasses are cut 
 into saw teeth, and these are edged with silica so 
 finely that they cut the flesh like knives. The mar- 
 gins and surfaces of thistle leaves and stems are 
 drawn out into spines, the protective value of which 
 may be easily seen. 
 
 The members of the cactus family protect their 
 bodies to a great extent by sharp spines, many of 
 which are harhed. These spines are modified leaves 
 which have lost the original function of such organs, 
 and have become solely organs of defence. 
 
124 THE NATURE AND WORK OF PLANTS 
 
 Animals, on the other hand, are constantly strivmg 
 to use the bodies of these plants for food without 
 injury from their weapons, and some of them suc- 
 ceed even with such well-protected forms as the 
 cactus and the thistle. Some grazing animals may 
 even eat poison ivy without harm. 
 
 171. Branches used as leaves. — A species may 
 find itself in a location to which its leaves are wholly 
 unsuited, and it may cease to develop these organs 
 in the usual way. In such instances branches are 
 sometimes modified to carry on the work that should 
 be done by the leaf. An example of this may be 
 seen in the "smilax " of the gardener, which is used 
 so profusely for decorative purposes. The slender, 
 thin bodies having the appearance of leaves are 
 really short branches, and the true leaves are to be 
 found as small colorless or brownish bracts at the 
 lower side of the base of these leaflike branches. 
 
 172. Tlie jpart of stems in the struggle for exist- 
 ence. — If the surface of the earth were level and 
 plain, and the number of plants were not so great 
 as to fully occupy this space, probably all species 
 would form short stems which would simply lift the 
 leaves and flowers fi'om the ground. 
 
STEMS 125 
 
 The number of individuals which attempt to grow 
 on any given spot, however, is many times greater 
 than it can support. The species which are capable 
 of sending up long stems quickly will reach the 
 sunlight and live while their slower and weaker 
 neighbors will be choked or shaded out. In this 
 fight the stem is the chief weapon. 
 
 173. Weeds. — In the cultivation of crop plants 
 all species are killed by the farmer except the one 
 desired, thus removing it from the struggle for 
 existence with neighbors. Certain forms, however, 
 have habits of growth which adapt them for gaining 
 a foothold among the cultivated forms, and this 
 makes them weeds. Before the country was settled 
 or cultivated there were no weeds, of course. Vigor- 
 ous and rapid growth of the stems is the principal 
 characteristic of weeds. The stems do not alwaj^s 
 stand erect, but may carpet the soil and hinder the 
 growth of other plants in this manner. Find and 
 describe the habits of three weeds. 
 
 174. Climbing stems. — In the struggle to get 
 the leaves and flowers up to the sunlight, a number 
 of species have formed the habit of clinging to the 
 stems of other plants. This is done by two methods : 
 
126 THE NATURE AND WORK OF PLANTS 
 
 the stem of the climber may coil or twine around the 
 body of the supporting plant, or it may attach itself 
 by means of roots or tendrils. 
 
 The hop and morning-glory are examples of the 
 twiners, and the circular movement of the tips of the 
 stems is one of the factors in coiling it round the sup- 
 port. Examine one of these plants, or a bean vine, 
 and note the firmness with which it is attached. 
 
 That plants climb by means of roots has already 
 been noticed (§ 28). The most effective climbing 
 devices, however, are tendrils. These are generally 
 modified stems, branches, flower stalks, or even 
 leaves. 
 
 Examine the tendrils of a squash, pumpkin, pas- 
 sion flow^er, or balsam apple (MicramjMlis). They 
 will be seen to be long slender bodies arising at the 
 nodes of the stem at the bases of the leaves. Ob- 
 serve their movement in the same manner as in the 
 stems (§152). The tendril appears to be curved, with 
 a hooked tip. Draw its exact outline. Now rub the 
 surface on the inner side of the curve with a pencil, 
 and look for changes in form. It curves at the place 
 touched. Take note of the time and extent of the 
 movement. If the pencil were held in place, the ten- 
 dril would coil around it. Look for instances of 
 
STEMS 127 
 
 tendrils which have just formed a coil around a sup- 
 port. Now observe the older tendrils toward the 
 base of the stem. What other action has the ten- 
 dril shown beside coiling around the support ? The 
 formation of the spiral coils shortens the tendril and 
 brings the stem nearer the support. Thus as the tip 
 of the stem elongates these organs are formed at 
 each node, and they revolve in the air until coming 
 in contact with a support: quickly coiling round 
 this, the free portion of the organ is thrown into a 
 coil lifting up the stem a distance of a few inches. 
 The force exerted in the lifting would raise a weight 
 of one to three ounces, which is much more than the 
 weight of the stem to which the tendril is attached. 
 Compare the action of the tendrils of three species. 
 After the body of the plant has been fastened to the 
 support by means of the tendrils, the coiled portions 
 act as springs in resisting the action of the wind or 
 any other force which would tend to tear the plant 
 from its support. Test this by hand. 
 
 175. 77ie irritability or sensitiveness of stems. — It 
 has been shown in a previous paragraph (§91) that 
 the light which shines on the leaf may send an im- 
 pulse to the stem to which it is attached, causing a 
 
128 THE NATURE AND WORK OF PLANTS 
 
 curvature which will place the leaf in the most 
 advantageous position for the performance of its 
 work. The stem is sensitive to light itself, as may 
 be shown if a specimen stripped of leaves is placed 
 near a window, when it can be seen to bend toward 
 the light. 
 
 176. Sensitiveness to gravity. — Select a vigor- 
 ously growing specimen of a tomato planted in a 
 pot, and place it with the stem in a horizontal posi- 
 tion. Observe the stem a day later. In what 
 region has the curvature taken place ? Repeat this 
 experiment with a grass. Note the stems of plants 
 in the woods and meadows which have been thrown 
 down by the wind or other causes, and the tips have 
 curved in response to gravity. This form of geotro- 
 pism is exactly the reverse of that exhibited by roots. 
 (See § 43.) Still another response to gravity is to be 
 seen in the lateral branches of coniferous trees and 
 trailing stems. These place their axes at right 
 angles to the action of gravity. Sometimes the 
 trailing habit is the result of the action of the plant 
 in placing its axis at right angles to the rays of light 
 which strike it. If the plant is placed in darkness, 
 it may be found whether the horizontal position is 
 
STEMS 129 
 
 the result of the action of gravity or light. If it is 
 the result of light, it will generally grow erect in 
 darkness. 
 
 177. Stems are found among the higher plants 
 only. — The seed plants and ferns only have true 
 stems as determined by the tissues which compose 
 them. The mosses, liverworts, and some of the sea- 
 weeds have a main axis from which branches are sent 
 off, and while it performs the work of a stem it has 
 not the true stem structures. A body of this kind 
 is termed a thallus. The main axis of the mosses, 
 liverworts, and the larger algae is often designated 
 as a stem, though it does not exhibit the distinction 
 of tissues shown by the true stems of the higher 
 plants. 
 
VII. THE WAY IN WHICH NEW PLANTS 
 ARISE 
 
 178. Distribution of the individuals of a species. 
 — Every species is represented by a number of 
 individuals. Sometimes this number is very great 
 and may run up into the millions. On the other 
 hand, there are a number of species of which but 
 few individuals have been seen, and some are so 
 rare that but a single specimen may have been 
 found. The individuals of a species may be scat- 
 tered across states and continents, or they may be 
 congregated in a meadow or on a single mountain 
 top. Thus, for instance, the common polypody 
 forms carpets or dense layers on rocks, that contain 
 several dozens of individuals, and these colonies may 
 be found almost throughout North America, Asia, 
 and Europe. The individuals of Adam-and-Eve, or 
 putty root, occur one or a few in a place, in a 
 broad belt of country that includes the northern 
 half of the United States and the southern half 
 of Canada. The Georgia oak {Quercus Georgiana) 
 
 130 
 
THE WAY IN WHICH NEW PLANTS ARISE 131 
 
 is found only on the granite slopes of Stone Moun- 
 tain in Georgia. 
 
 Every species originated in some one locality, and 
 it spreads its seeds or spores by various methods. 
 The spores or seeds find a foothold wherever they 
 may in suitable places. Probably no species has 
 succeeded in sending seeds or spores to all of the 
 places which would be suitable for its growth. As 
 the species spreads across a continent, it may meet 
 barriers in the form of seas, mountains, or other 
 obstacles which stop its progress. 
 
 179. Methods of reproduction. — The life of each 
 individual is limited, and no matter whether the 
 number is great or small, if each does not constantly 
 give rise to new individuals the species would soon 
 become exterminated. Furthermore new individuals 
 must be produced as fast as the older ones die, or 
 extermination will result. Numerous species of ani- 
 mals have disappeared in the memory of man, but 
 modern examples of the extinction of plants are not 
 common, although the earth's crust is rich with the 
 remains of species existent in former geologic periods. 
 A tree belonging to the sunflower family, once found 
 on the island of Saint Helena, is known to be ex- 
 
132 THE NATURE AND WORK OF PLANTS 
 
 tinct. There are three principal methods by which 
 new individuals may be formed : vegetative repro- 
 duction by means of cuttings, huds, branches, etc., 
 simple or asexual spores, and egg formation. 
 
 180. Hej^roduction by cuttings. — Select a good 
 healthy leaf of a begonia, cut it from the stem, 
 trim away nearly half of it, and put the raw edge 
 in sand kept moist in a shallow dish or box. Ex- 
 amine every week for a month. Roots will first be 
 formed, and then if the experiment is allowed to 
 run long enough a stem will appear, which will in 
 turn bear leaves like the original from which the 
 cutting was made. It is seen that the begonia is 
 able to replace the entire plant from part of a leaf 
 — a capacity that is shared by an extremely large 
 number of species. 
 
 181. TJie stem may rejjroduce the entire plant. — 
 Cut a small twig of the willow, a stem of the ge- 
 ranium, coleus, or begonia, and insert in moist sand 
 as above. A few weeks later the cutting will be 
 found to have replaced the missing roots and leaves 
 and made a complete plant. 
 
 182. Tlie root may reproduce the plant. — Cut off 
 a portion of the fleshy root of a sweet potato or 
 
THE WAY IN WHICH NEW PLANTS ARISE 133 
 
 horse radish, and put in moist sand or soil. Stems 
 and leaves will be seen to appear after a time. The 
 ability to replace the other members of the plant 
 by the root is not very common. It is shared, how- 
 ever, by beech, cherry, poplar, and some coniferous 
 trees. 
 
 183. Structures used hy 2^^ants as means of vege- 
 ^tative reproduction. — Plants have many devices by 
 which portions of the roots, stems, and leaves take 
 on special forms and become separated from the 
 parent plant in a manner which allows them to form 
 a new individual. Chief among these structures are 
 bulbs (see § 167), hidhils, tubers, offsets, stolons, besides 
 many special forms. 
 
 184. Tubers. — -A tuber consists of a portion of 
 an underground stem which serves as a storehouse 
 for surplus food, and which is capable of reproduc- 
 ing the plant by the growth of its buds, which are 
 usually several in number. Examine the base of a 
 vigorous potato stem by digging away the soil. Be- 
 sides the roots will be found numbers of thickened 
 stems or potatoes. Note the " eyes," or buds, on 
 the surface. Are they most abundant on the end 
 toward the main stem or the apical end ? 
 
134 THE NATURE AND WORK OF PLANTS 
 
 The main stem dies at the close of the season, 
 leaving the tubers in the soil, and if each were 
 capable of giving rise to one plant alone, the parent 
 plant would be followed by a dozen or more the 
 next season. This does not express the full repro- 
 ductive power of the tubers, however. In the plant- 
 ing of " seed" potatoes to obtain a crop, the farmer 
 cuts the tubers into pieces each of which contains an 
 " eye " and is capable of giving rise to a new plant. 
 As a consequence the tubers of a single plant may be 
 capable of producing over a hundred new individuals. 
 
 Secure a large, sound potato in January and put 
 it in the mouth of a large bottle filled with water, 
 or a cup or tumbler, cover with a glass dish and set 
 in a living room. Renew the water and clean the 
 bottle occasionally. Note the manner in which the 
 buds begin to grow and their location. Do all 
 the buds awake ? If several experiments have been 
 set up, you can awaken the sleeping buds by destroy- 
 ing the active ones. Are new roots formed on the 
 tuber or on the stems? Observe the behavior of 
 potatoes which have sprouted in a dark cellar. 
 
 185. Bulbils and hulhlets. — It has been shown 
 how the underground branch enclosed in a bud 
 
THE WAY IN WHICH NEW PLANTS ARISE 135 
 
 may increase in thickness, and develop its sheathing 
 scales in such manner as to form an onion or other 
 bulbs. The buds in the upper axils of a shoot may 
 also exhibit this same action, but the resultant 
 structures are generally smaller and are termed 
 hulhils or hulhlets by some authors. Thus the onion 
 may produce the last-named formations on the 
 upper ends of its stems. In this instance the bulb- 
 let replaces the flower bud. This behavior may be 
 noted in the cultivated onion as well as in the wild 
 garlic {Allium vineale L.), meadow garlic [Allium 
 Canadense.L.), sometimes in the wild onion {Allium 
 mutabile Michx). 
 
 The conversion of a leafy bud into a bulblet is 
 to be seen in the tiger lily, in which small blackish 
 bulblets covered with three or four scales are to be 
 found in the upper axils. These may germinate as 
 soon as they fall to the ground, and sometimes send 
 out roots before they are detached from the parent 
 plant. The bulblets of the lily as well as those of 
 the dioscorea, a member of the yam family, will 
 endure long periods of drought and low temperature 
 without injury. 
 
 The bulb-bearing loosestrife, found in marshes and 
 damp thickets in Northern United States, forms 
 
136 THE NATURE AND WOBK OF PLANTS 
 
 reddish cigar-shaped bulbils in the upper axils of the 
 stems, which consist of a thickened branch sheathed 
 by blunt scales. These structures drop from the 
 plant in the autumn, and those which fall in the 
 water, or those which are covered up by falling 
 leaves, escape frost and germinate in the following 
 spring, reproducing the plant. Those that drop into 
 the water may be carried away by currents, and 
 thus spread the species into unoccupied territory. 
 
 Cystopteris (C. hulbifera), a common fern, forms 
 numerous -bulblets on the lower surfaces of the mid- 
 ribs, which drop off in the autumn and germinate in 
 the spring. 
 
 186. Division of the body hy the death of j)cirt of 
 it. — Some of the liverworts, club-mosses, ferns, and 
 many of the seed plants have creeping underground 
 stems which branch in the form of a letter Y. By 
 the death of the older part of the stem, representing 
 the base of the Y, the two branches are left as 
 separate plants. These extend, branch, and divide in 
 the same manner. Note this process in the com- 
 mon liverwort (Marchantia, or Conocephalus), in the 
 rhizomes of the fern and club-moss. It may be seen 
 also in the creeping grasses. 
 
THE WAY IN WHICH NEW PLANTS ARISE 137 
 
 187. Division among the simjjle ^;?a?i^s. — Among 
 the forms in which the body consists of a single cell 
 new ones are formed by the division of a parent cell, 
 and the two halves quickly grow to the size of the 
 original cell, when they divide in turn. Such organ- 
 isms grow with great rapidity, and this method gives 
 rise to a large number of individuals in a very short 
 time. But fifteen or twenty minutes are necessary 
 to enable each cell to attain full size and divide. By 
 this method a single cell of a bacterium may produce 
 sixteen million others in eight hours, and in a day 
 many millions of millions. 
 
 188. Runners. — Many species of seed plants 
 send out long branches with slender internodes from 
 the bases of the main stalks, and these lie on the 
 surface of the ground forming roots at each joint or 
 node. Leaves are also formed, and later an upright 
 stem. Then the runner itself dies away, leaving a 
 young plant to mark the position of each node. 
 This process may be followed in any strawberry 
 bed, and is a very efficient method of spreading the 
 plant. 
 
 189. Stolons. — The dewberries of pastures, some 
 raspberries, and other plants, form slender stems 
 
138 THE NATURE AND WORK OF PLANTS 
 
 which finally lean over with their tips touching 
 the ground. Roots are formed at this point, and 
 the growth of leaves and a new main stem quickly 
 follows, making a new individual. 
 
 190. Dissemination or sjoreading of the 2^^<^nt hy 
 vegetative propagation. — In all of the above methods 
 by which new individuals are formed from portions 
 of the body of a parent plant, the new specimen 
 finds a foothold a greater or less distance from the 
 parent. Each successive set of new plants is still 
 farther away from the starting point, and it is to be 
 seen that any species might travel considerable dis- 
 tances by such seemingly slow methods. Thus some 
 of the young plants formed by the runners of a 
 strawberry will be five feet from the parent, and as 
 these quickly give rise to similar runners the species 
 would travel across a large meadow in a few years. 
 
 191. Ge7nmce. — If the upper surfaces of flat 
 fronds of Marcliantia ov' Lunularia are examined, 
 small circular or crescent-shaped receptacles will be 
 seen containing a number of globose masses of green 
 tissue either loose or easily detached. These are 
 the portions of its body devised to reproduce the 
 species vegetatively, and are termed gemmce. If 
 
THE WAY IN WHICH NEW PLANTS ARISE 139 
 
 placed on damp soil covered with a dish in a warm 
 room, they may be seen to germinate. 
 
 192. Be2:)7'oduction hy sjjores. — Instead of cut- 
 ting off a member of its body for the purpose of 
 giving rise to new individuals, the plant may develop 
 special masses of reproductive tissue. When these 
 masses reach maturity, they divide into a number 
 of separate cells, each of which is capable of giving 
 rise to a new individual upon germination r The 
 origin of new individuals in this manner is termed 
 asexual rej^roduction, and the spores in a puff ball, 
 or those on the under side of a fern leaf, exhibit 
 this action. 
 
 193. JReprodiiction hy eggs. — In another method 
 of reproduction the plant develops two kinds of 
 reproductive tissue, and when these are mature a 
 cell from each unite to form a fertilized egg, which 
 then is capable of giving rise to a new individual. 
 The two kinds of reproductive elements are termed 
 gametes, and the origin of new plants by this method 
 constitutes sexual rejjroductio?!. 
 
 194. Fern spores. — Examine the under side of 
 the leaves or fronds of the polypody or any com- 
 mon fern in the autumn. A number of brown spots, 
 
140 THE NATURE AND WORK OF PLANTS 
 
 masses, or areas will be seen. After they are com- 
 pletely ripe, strike a sheet of white paper with the 
 frond. A quantity of brownish particles will be 
 thrown out on the paper. Examine with a lens. 
 They appear to be roughened balls or egg-shaped 
 masses. These are the asexual spores of the fern. 
 Now examine the masses on the fern leaf with the 
 lens. The spores have been enclosed in flasks or 
 capsules with short stalks. Sometimes the collec- 
 tion of capsules is covered with a shield, or by the 
 upturned edge of the frond. 
 
 Secure a small piece of a leaf of any common 
 fern with mature spore cases. Allow it to become 
 quite dry. Now lay it with the spore surface 
 upward on a sheet of white blotting paper satu- 
 rated with water, and cover with a glass dish. 
 Remove the dish and examine a day later. Numer- 
 ous brown spores will be seen scattered over the 
 blotting paper in all directions. The spores are 
 thrown out in a cloud by ferns in damp weather 
 by the action of the capsules in which they are 
 formed. 
 
 A great many of the mosses and liverworts are 
 known also to reproduce themselves by means of 
 various kinds of bulbils, cuttings, and similar parts. 
 
TUE WAT IN WHICH NEW PLANTS ARISE 141 
 
 and this in many cases is the only way which they 
 have of perpetuating the species. 
 
 195. Germination of spores. — Take a small piece 
 of soft brick, and boil it thoroughly to kill all 
 organisms attached to it. After it has been in 
 the water for an hour, remove and set in a saucer 
 of spring water. Cover with a tumbler. After it 
 is cool sprinkle spores from some fern liberally over 
 its surface. Replace the cover. Heplenish the water 
 in the saucer from time to time, keeping it in a com- 
 fortable living room in a dark corner. After a few 
 weeks a number of greenish bodies will be seen on 
 the brick. These have been produced by the ger- 
 mination of the spores. 
 
 196. Another form or generation of the fern. — 
 The bodies produced by the germination of the spores 
 are like small irregular leaves, and they are seen to 
 adhere to the brick by means of hairs or rhizoids, 
 which serve the purpose of fixing and absorbing 
 organs. Now these flat bodies must be fern plants 
 because they came from the spores of a fern. Theu' 
 relation to the ordinarily known form may be as- 
 certained if the culture is kept in order for a few 
 weeks longer. Small upright stalks will appear, 
 
142 THE NATURE AND WORK OF PLANTS 
 
 bearing a minute leaf which gradually enlarges 
 until it resembles that of the plant from which the 
 spores were taken. A root may also be found. This 
 young plant is attached to the leaflike body and 
 apparently sprang from it. The young plant with a 
 stem will enlarge, and if placed in the soil it would 
 develop spores like those which were placed on the 
 brick, and the life history of the species would be 
 complete. 
 
 197. Alternation of generations. — In the complete 
 life of the fern it is found to develop two indi- 
 viduals entirely different in form, and each gives 
 rise to the other. This is known as the alternation 
 of generations. One generation is constructed with 
 a root, stem, and leaves, and it develops single 
 spores which are capable of giving rise to the other 
 generation. This large plant which is known to the 
 ordinary observer is the sporopliyte. The other gen- 
 eration is a thallus, or prothallus, and the body con- 
 sists of a thin sheet of cells bearing green color, and 
 furnished with rhizoids for absorption and fixation. 
 This generation develops two kinds of reproductive 
 cells in little flasks on the lower side of the pro- 
 thallus. The flasks containing the male gametes 
 
THE WAY IN WHICH NEW PLANTS ARISE 143 
 
 (§ 193) burst, and these elements find their way to tlie 
 other flaslis where tlie female gametes are developed, 
 and one male gamete fuses with the female gamete, 
 and the new cell thus formed gives rise to an indi- 
 vidual of the other generation, which is the common 
 fern plant. The prothallus form of the fern is then 
 the gametojjJiyte. In the fern the sporophytic gen- 
 eration is seen to be much the larger, and the higher 
 one follows the development of the plant kingdom 
 the greater will be the size of the sporophyte, and 
 the smaller will be the gametophyte. On the other 
 hand the gametophyte attains greater importance 
 in some of the lower forms, as may be seen in the 
 moss. 
 
 198. TJie two generations of the moss. — Secure 
 a clump of a large moss, some of the specimens of 
 which may be seen to be in " fruit." Examine one 
 of the specimens which is not in "fruit." It will 
 be found to consist of a small leafy stem, with per- 
 haps rootlike organs arising from the lower end and 
 furnished with rhizoids for absorption. The upper 
 extremity of the stems bears leafy cups, in which are 
 the organs containing the two kinds of gametes. This 
 is the gametophyte of the moss. The male gametes 
 
144 THE NATURE AND WORK OF PLANTS 
 
 fuse with the female gametes, as m the fern, and the 
 cell formed germinates without leaving its place as 
 in the fern, but the structure of the individual 
 formed is very much different. The second genera- 
 tion consists of a slender brownish or greenish stem, 
 bearing a large capsule. This capsule is composed 
 of tissue which contains chlorophyl, is furnished 
 with a hood or other appendages, and contains a 
 flask or sac, the contents of which develop into 
 spores. The spores germinate and form the leafy 
 stemmed plants examined at first, and the capsule 
 and its stalk are thus the sporophyte of the moss. 
 It is seen to be able to form some of its food by 
 means of its chlorophyl, but it is dependent upon 
 the gametophyte for its supply of water and mineral 
 salts, and is sometimes said to be parasitic upon it. 
 
 199. Occurrence of generations. — This alterna- 
 tion of the two generations of a species is not inva- 
 riable. It was found that by vegetative methods 
 of reproduction (§ 180) the cutting reproduces its 
 own generation in all the experiments tried. There 
 are some instances, however, where the cutting of a 
 sporophyte will produce a gametophyte, and vice 
 versa. Then, again, the spores developed by the 
 
THE WAY IN WHICH NEW PLANTS ARISE 145 
 
 sporophyte often grow into sporophytes upon ger- 
 mination. This is found in mushrooms and moulds. 
 The mould which grows upon moist bread develops 
 small sacs filled with spores, which take a black or 
 brown color when ripe. These spores germinate 
 and grow individuals exactly like those from which 
 they sprung, without the formation of another gen- 
 eration. The asexual spores of the sporophyte may 
 be observed if the umbrella-like top of a mushroom 
 is carefully taken off and placed on a sheet of white 
 paper for a day or two. The spores which are borne 
 on the thin plates or gills on the under side of the 
 cajj are set free and fall upon the paper in great 
 number. The germination of these generally pro- 
 duces a sporophyte. 
 
 200. The generations of the seed plants. — The 
 species which produce flowers and seeds have two 
 generations, but the gametophyte is so small that 
 its behavior may not be seen without the use of 
 special methods of observation with the compound 
 microscope. 
 
 201. The gametophyte, or egg-hearing generatio7i 
 in the seed plant. — It was shown in the life history 
 of the fern that unlike cells from different parts of 
 
146 THE NATURE AND WORK OF PLANTS 
 
 the body of the gametophyte were united to form 
 the fertilized egg from which a new plant was 
 formed, though this is not always the case. In the 
 seed plants, however, the two kinds of gametes are 
 produced on different individuals, which are borne 
 on separate organs of the sporophyte, or on sepa- 
 rate plants. Thus the male gamete is produced in 
 a minute individual formed by the germination of 
 the pollen, and the female gamete in another im- 
 bedded deeply in the ovary. 
 
 202. The structure of a floiver. — Secure a 
 fresh supply of flowers of the apple. This may 
 be done in winter by bringing in some twigs 
 of these trees, in the latter part of the winter, 
 and placing the lower ends in water for two or 
 three weeks before needed. The preparation should 
 be kept in a comfortable living room near a win- 
 dow. A supply of these or other suitable species 
 may be found out of doors during the proper sea- 
 son. When the fully opened blossoms have been 
 secured, note that the flower appears to sit in a 
 cup the upper edges of which divide into five leaf- 
 like bodies. The shape, size, and arrangement of 
 these will vary greatly in the several species 
 
THE ]VAY IN WHICH NEW PLANTS ARISE 147 
 
 selected for observation. The separate parts of 
 this cup, or circle, are usually termed sepals, and 
 while they serve important uses in protecting other 
 parts of the flower, or the fruit, yet they are not 
 essential to reproduction, and are lacking in many 
 species. Immediately inside the sepals is a circle 
 of five large colored leaves, forming the most 
 showy part of the flower; these are the ^:>e^'«fe. 
 Like the sepals, they also exhibit great diversity 
 in number, size, shape, and color in different species. 
 Some are most beautifully painted and marked, 
 and it is principally to the development of these 
 organs in various plants that the florist's art is 
 directed. These organs, also, play only a minor 
 part in reproduction, and are lacking in many 
 species. 
 
 Immediately inside the petals are to be seen a 
 number of small knobs, or flasks, not much larger 
 than a pin's head, borne on curved stalks. These 
 are the stamens, and if the flasks are crushed or 
 torn open, they will be found to contain a yellow- 
 ish powder made up of a great number of j^ollen 
 grains. In the centre of the flower are five small 
 stalks extending up into the air, the styles. The 
 expanded surface of the tip are the stigmas. The 
 
148 THE NATURE AND WORK OF PLANTS 
 
 lower end of these styles terminates in a capsule 
 buried in the tissues at the base of the flower. 
 This capsule, if carefully cut across with a sharp 
 knife, will be found to be divided into five cham- 
 bers, correspondent to the number of styles, and it 
 is termed the ovary ^ because it is in this organ that 
 eggs are formed. The ovary, styles, and stigma con- 
 stitute the ^:)^s^^7. 
 
 Almost any flower will suffice for observations 
 of the above character. A dozen or more different 
 kinds should be examined, noting the number, size, 
 and arrangement of the different organs. The 
 greatest diversity will be found, indicating that 
 the separate species accomplish the work of re- 
 production in a manner characteristic of them- 
 selves. 
 
 The flower described above is said to be perfect, 
 but in others the stamens and pistils are in separate 
 flowers on the same or different individuals. The 
 petals or the sepals may be absent or replaced by 
 circles of bracts. What is the arrangement of the 
 organs in the jack-in-the-pulpit, spring beauty, but- 
 tercup, the ash tree, willow, beech, maple, and oaks ? 
 Examine also the flowers of the lily, trill ium, lark- 
 spur, bean, and geranium. 
 
TUE WAY IN WHICH NEW PLANTS ARISE 149 
 
 203. Spores of seed jjlants. — The sporopliytes of 
 seed plants produce two kinds of spores. One is 
 formed in the stamen and forms the pollen grains, 
 and the other grows in the ovary and produces the 
 gametophyte which bears the egg cells. 
 
 204. Pollination. — In order to complete the 
 life history of the plant it is necessary that the 
 pollen grains should be transported to the stigmas, 
 or upper extremities of the pistils, where they may 
 germinate and send a long tube down to the 
 ovaries. Furthermore, it is important in a great 
 number of species that the pollen from one plant 
 should be carried to the pistils of another, a pro- 
 cess termed by the botanist cross 2^ollination. The 
 seeds and seedlings obtained by this method are 
 much stronger and represent the species more per- 
 fectly in most instances than those which result from 
 the action of the pollen upon the pistil of the same 
 flower. The various devices by which this cross 
 pollination is secured are almost without number. 
 One method by which the pollen of any flower 
 is kept from its own pistil is to have the stamens 
 and pistil mature at different times. In other 
 cases the stamens are below the pistils, so that 
 
150 THE NATURE AND WORK OF PLANTS 
 
 the pollen would fall away from instead of upon 
 the pistil of the same flower. Having guarded 
 against self-pollination, the plant must next be pro- 
 vided with means of securing pollen from other 
 flowers for all the pistils. The principal agencies 
 which it makes use of in this work are the wind 
 and animals, principally insects. 
 
 205. T7ie ivind as an aid to pollination. — More 
 than ten thousand species are known to make use 
 of the wind as an agency in carrying the pollen from 
 one flower to another. In order to do this success- 
 fully great quantities of pollen are produced and 
 thrown into the air upon the opening of the pollen 
 sacs, and then float upon the currents of air, some of 
 them alighting upon the stigmas of other flowers. 
 The pines, oaks, beeches, hazels, birches, poplars, 
 walnuts, mulberries, and some maples throw their 
 pollen into the air and allow it to float to other 
 flowers in this manner. It is a matter of common 
 knowledge that when a single row of corn is planted 
 in a field with no other collection of the same in the 
 vicinity, generally no seeds are produced. This will 
 always be the case if the row is at right angles to the 
 prevailing winds. The pollen of the pines is often 
 
THE WAY IN WHICH NEW PLANTS AIIISE 151 
 
 thrown into the air in such quantities that it is 
 deposited upon the ground, making a " shower of 
 sulphur." 
 
 206. Animals as I'^ollen carriers. — The flowers 
 of many species are provided with means of attrac- 
 tion to certain animals, principally insects, and dur- 
 ing their visits pollen adheres to their bodies and 
 is carried to the next flower. The attraction may 
 be nectar or honey, the pollen itself, a place for 
 the deposit of eggs, or the flower may offer the 
 insect a suitable place of refuge or lodgment for 
 the night or during a storm. The description of 
 the various methods by wdiich this is done would 
 fill a large book, and may not find place here. On 
 a favorable day in the spring or summer the student 
 should find a flower which is frequented by insects, 
 and note the manner in which this visit is made. 
 First determine the object of the visit. Then note 
 what parts of its body rub against the stamens and 
 pistils. Catch one of the insects, and examine its 
 body for traces of pollen. Examine a number of 
 flowers late in the evening or early in the morning 
 for animals which have lodged in them during 
 the night. 
 
152 THE NATURE AND WORK OF PLANTS 
 
 207. Fertilization. — When the pollen is carried 
 to the flower which it may benefit, it can only be of 
 use if it is deposited on or near the stigma at the top 
 of the pistil. Here it finds a sweetish and sticky 
 substance made up of cane sugar and ghicose which 
 it uses as food in any growth it may make. If 
 properly placed on this stigma, the presence of this 
 sweetish substance starts it to germinating. A long 
 slender tube is produced, making a structure much 
 as if the head of a pin were to grow out and form 
 the body of the pin. The pollen tube is generally 
 very crooked and it bores into the sticky substance 
 in which the pollen grain is imbedded, and then 
 grows down into the style in an effort to get away 
 from the oxygen of the air. Not only does it strive 
 to get away from the oxygen of the air, but certain 
 substances in the ovary attract it. Now the tube 
 formed by the grain or pollen is a part of a gameto- 
 phyte, and near its tip it contains a minute mass of 
 protoplasm, which is the male gamete which is to 
 be carried to the egg. The embryo sac in the 
 ovary contains the female gametophyte bearing an 
 egg cell, and the pollen tube extends to it, carry- 
 ing the male gamete in its own tip. The union of 
 the gamete from each constitutes fertilization, and 
 
THE WAY IN WHICH NEW PLANTS ARISE 153 
 
 the result is a structure from which a new sporo- 
 phyte is formed. The ovary may be compound and 
 contain many embryo sacs, in which case a separate 
 pollen tube will be necessary to fertilize each one. 
 The result will be many seeds or embryos separate 
 or in a many-seeded fruit. The growth of the pol- 
 len tube down through the pistil to the embryo sac 
 may take only a few hours, or it may occupy a year, 
 as in the pines. Shortly after the fertilization of the 
 egg it begins to grow and divide until an embryo 
 plant of the sporophytic generation is formed, hav- 
 ing possibly a root, a stem, and one, two, or more 
 seed leaves with the main growing point of the 
 future stem. 
 
VIII. SEEDS AND FRUITS 
 
 208. The seed. — After the embryo has reached 
 a certain stage of development it becomes quiescent 
 and remains so until the time and opportunity ar- 
 rives for it to grow in the germination of the seed. 
 During the development of the embryo from the egg, 
 reserve foods for its use during germination in the 
 shape of oil, starch, sugar, or j^rotei?! may be depos- 
 ited in its seed-leaves, or in the seed-coats, or in other 
 organs developed for that purpose. 
 
 209. The existence of the seed. — Generally about 
 the time that the embryo has completed growth and 
 the deposit of food has been made, the seed or fruit 
 is separated from the parent plant, though this is 
 not always the case. Germination of the seed takes 
 place when it secures proper conditions of season, 
 tnoisture, and temjjeratiire. This may be in a few 
 days or several years. Some seeds actually grow 
 before separation from the parent plant, while others 
 may remain quiescent during the lifetime of a man. 
 
SEEDS AND FRUITS 155 
 
 Stories are current of seeds being taken from 
 mummy cases six thousand years old v/liicli showed 
 powers of germination, but such statements are not 
 authentic. Instances are known in which certain 
 species have lived three hundred or even four hun- 
 dred years, but these probably represent the limit 
 attainable by only a few plants. Ordinary forms, 
 such as wheat and corn, may not live longer than 
 fifteen or twenty years at the utmost, and the 
 seeds of nearly all cultivated plants begin to show 
 lessening powers of germination after a year. 
 Some are totally worthless the second year. 
 
 210. Fruits. — In addition to the coats formed 
 around the seed the portions of the ovary in con- 
 tact with the seed are often developed in certain 
 ways of benefit or assistance in the protection, dis- 
 semination, or germination of the seeds. The seed 
 and all of the parts of the ovary adhering to it 
 constitute a fruit. The study of the structure and 
 behavior of the fruit after the ripening of the seed 
 will therefore be of great interest. 
 
 211. The cocoanut. — The fruit of Cocos niici- 
 fera offers a most interesting object for the illus- 
 tration of the action and structure of the fruit of 
 
156 THE NATURE AND WORK OF PLANTS 
 
 a palm. The material necessary for the work con- 
 sists of a few stripped nuts, such as are offered for 
 sale in every village, and some from which the 
 husks have not been taken. The latter may be 
 obtained from merchants dealing extensively in 
 tropical fruits. 
 
 Two or more each of the whole fruits, and the 
 same number of stripped nuts, should be placed in 
 moist sawdust or soil in a box two or three times 
 its size, and kept in a comfortable living room or 
 greenhouse if the work is to be done in winter. 
 In the summer it may be placed in the ground 
 like any seed. The time necessary for germination 
 is from six to ten weeks. This will furnish ger- 
 minated seeds for examination, and will also show 
 whether the husk is necessary for germination or not. 
 
 I. Size and appearance of the fruit. 
 
 Make an examination of the entire fruit, and 
 note : — 
 a. The shape of the base and apex, and gen- 
 eral form of fruit. Three wide short 
 tracts may be found adhering to the 
 base ; these are from the envelopes of 
 the flower, and may be the calyx. The 
 
SEEDS AND FRUITS 157 
 
 blunt angles may be seen to run from 
 the base to the apex. Draw. 
 b. Measure the circumference, length, and 
 diameter. Place in a bucket of water. 
 Does it float? Will the stripped nut 
 float? Plunge the fruit into a bucket 
 exactly filled with water. Remove and 
 refill the bucket. The amount of water 
 necessary to refill the bucket will be the 
 volume of the fruit. Many of the fruits 
 drop from the trees into tlie water of 
 streams, ponds, and tides, and are carried 
 long distances before they lodge and ger- 
 minate. The planters place the fruits in 
 the margins of salt lagoons and marshes, 
 and the salt is supposed to hasten the 
 process of germination. 
 
 II. Structure. 
 
 Cut through a fruit crosswise by means of a 
 sharp saw, and note : — 
 a. The husk, the outer layer of which is smooth 
 and firm, while the mass is composed of 
 strong fibres and 2^ith. Observe the at- 
 tachment of the husk to the shell. 
 
158 THE NATURE AND WOEK OF PLANTS 
 
 h. Strip the husk from the entn^e fruit, and 
 note its rehitive thickness over different 
 parts of the shelh Note also the charac- 
 ter of the fibres at the basal end. The 
 husk is derived from the wall of the 
 ovary. If the fruit were suspended on 
 its stem and were broken off suddenly, 
 which end would strike the ground first ? 
 Do you think this beneficial or not ? 
 Examine the stripped nut and note : — 
 
 c. The shape and markings of the shell. The 
 
 three dark circular areas on the basal end 
 are the marks of the three parts or car- 
 pels of the ovary. 
 Break or cut up the nut and test — 
 
 d. The hardness of the shell. Cut with knife 
 
 and test strength. Is it " air tight " and 
 " water tight " ? 
 
 The husk is derived from the outer 
 wall of the ovary, and the shell from the 
 inner wall, neither being seed-coats. 
 
 III. Tlie seed. 
 
 Examine the nut which has been cut, and note : — 
 a. The central cavity, filled with a sweetish 
 
SEEDS AND FRUITS 159 
 
 clear fluid, the " milk." Determine the 
 capacity of this central cavity. 
 
 h. The white layer of " meat," the endosjjerm, 
 which is composed of storage cells con- 
 taining reserve food. Apply a drop of 
 iodine as a test for the presence of 
 starch. The endosperm plainly con- 
 tains oil, for it is expressed in great 
 quantities in factories. Sugar may be 
 detected by the taste. Split off por- 
 tions of the endosperm and measure its 
 thickness. 
 
 c. A brownish membrane will be seen adher- 
 ing to the outer surface of the endo- 
 sperm, which is made up of the true 
 seed-coats. 
 
 IV. TJie embryo. 
 
 Working from the inside, carefully cut away the 
 endosperm from around the eyes. 
 a. Under one of them will be found an irreg- 
 ular white cylinder, about a third of an 
 inch long, with the outer flattened end 
 pressed against the seed-coat, and the 
 inner portion buried in the endosperm. 
 
160 THE NATURE AND WORK OF PLANTS 
 
 This is the young plantlet. There was 
 originally an egg apparatus under each 
 eye, but two of them have not been 
 given an opportunity for development, 
 and the whole ovary is devoted to the 
 nourishment and protection of one em- 
 bryo. Rarely two embryos are per- 
 fected in one fruit, making twin trees 
 when they germinate. Make a drawing 
 of the embryo. 
 
 V. Germination. 
 
 Carefully cut away one side of the germinated 
 fruit, being careful not to injure the young 
 plant, and note : — 
 a. The absorbing organ, the inner end of the 
 embryo, which is made of the cotyledon, 
 has developed a mass of tissue, very 
 much the shape of a puff-ball, which is 
 at first the size of a marble, but which 
 gradually enlarges until it fills the cav- 
 ity of the nut. It uses the milk for 
 food as it grows, and furthermore it 
 secretes digestive fluids (enzyms), which 
 dissolve the starch and oil in the endo- 
 
SEEDS AND FRUITS 161 
 
 sperm, about as it would be done in the 
 human stomach. The fluid thus ob- 
 tained is conveyed back into the young 
 plant and serves as food. The endo- 
 sperm may be seen to be thinner where 
 the absorbing organ has touched it. 
 The amount of food furnished by the 
 endosperm is so great that the plantlet 
 may be nourished many months from it 
 alone, and generally it is entirely con- 
 sumed, remaining sweet and sound as 
 long as a trace is present. 
 The outer end of the cylindrical part of the 
 embryo contains the plumule, or young 
 shoot of the plant, and the root, which 
 pushes through the eye, breaking the thin 
 layer of the shell at that point, when 
 the plumule, a conical mass of firm 
 leaves, bores upward through the fibres of 
 the husk. When light is reached, green 
 leaves are formed. 
 
 The main root goes downward, send- 
 ing out branches which break through 
 the husk at various points, finally pene- 
 trating; the soil. If the fruits have been 
 
162 THE NATURE AND WORK OF PLANTS 
 
 germinated in the spring, the plantlets 
 may endure the summer out of doors in 
 almost any part of the United States. 
 
 The cocoanut has its original habitat 
 in the Eastern hemisphere, but now 
 occupies the tropics around the globe. 
 This wide distribution has been secured 
 by the agency of wind and water, and 
 by the attractive power of the food, 
 stored up in the endosperm, for tribes of 
 savage and civilized men. 
 
 212. The date. — The fruit of the commercial date 
 may be easily obtained, and used to illustrate the 
 action of the fruit of a second palm. 
 
 Secure a few dozen dried dates, such as are sold 
 by grocers and confectioners, and place a dozen in 
 the soil in a pot kept at a temperature about equal 
 to that of a comfortable living room, three or four 
 weeks before the observations are to be begun. 
 Strip the fleshy part of the fruit of a second dozen 
 and put in a second pot and place with the first. 
 This will show whether the edible flesh is of any 
 benefit in the actual process of germination. Soak 
 another lot in water for two weeks for dissection. 
 
SEEDS AND FRUITS 163 
 
 I. The appearance of the fruit. 
 
 Place some of the fruits in water for an hour, 
 and then note : — 
 a. The general appearance, size, and form. 
 h. The outer covering ; is it a distinct mem- 
 brane, or a part of the flesh underneath, 
 as in tlie husk of the cocoanut ? 
 c. The edible, fleshy portion ; is it attached to 
 the seed ? 
 
 IT. Tlieseed. 
 
 a. Describe the form of the seed. 
 
 h. Test the hardness and brittleness of the 
 seed and its coats. Crush or break the 
 seed to determine its firmness. 
 
 c. Cut away the coats from the surface of 
 
 the seed opposite the groove, and note 
 the position of the tip of the main root 
 of the embryo. 
 
 d. Cut the seed across and take out the em- 
 
 bryo. Describe its form and draw. 
 
 III. Germination. 
 
 Cut across some of the germinating seeds in the 
 same manner, and note: — 
 a. Ahsorhing organ, the cotyledon, here as 
 
164 TEE NATURE AND WORE OF PLANTS 
 
 in the cocoanut, serves as a digesting 
 and absorbing organ. It develops as 
 a cylindrical mass, and its juices corrode 
 the hard cellulose of the seed which is 
 stored as food for the young plantlet. 
 The absorbing organ expands until it 
 consumes all of the cellulose, and finally 
 fills up the entire space inside the coats. 
 b. Sketch the development of the basal end 
 of the cotyledon. It elongates and 
 forces the embryo stem tipped with the 
 root downward through the soil. As it 
 does so it opens at one side and allows 
 the first green leaf of the plumule to 
 come out. Finally the root begins to 
 develop, and it continues the downward 
 course taken by the cotyledon. If the 
 seeds were in the dry soil in which 
 the plant grows, the root and cotyledon 
 would bore down more than a yard be- 
 fore any branches would be given off. 
 But in the pot cultures this is impossi- 
 ble and unnecessary, for the plant finds 
 sufficient moisture near at hand. So far 
 as can be found from an examination of 
 
SEEDS AND FBUITS 165 
 
 the date seed, without seeing the plant 
 in its native habitat, the only manner in 
 which this fruit would secure the dis- 
 semination of the seed would be by 
 means of its pleasant tasting fruit, 
 which would cause it to be sought for 
 food by animals in general, some of 
 which, including man, in using it would 
 carry the fruit some distance from the 
 parent tree. This use of the fleshy 
 portion for food does not in any way 
 affect the germinating power of the seed, 
 so long as it is not cooked. Further- 
 more, the seeds are capable of enduring 
 great extremes of heat and cold, and 
 may lie around on the surface of the 
 soil for months or even years, and then 
 grow when the proper conditions for 
 germination are given them. 
 
 213. Maize, or Indian corn. — Maize, or the ordi- 
 nary Indian corn, is a third example of the plants 
 belonging to the same general group as the palms, 
 and it is even more interesting than the fruits 
 just examined. In order to see clearly the pur- 
 
166 THE NATURE AND WORK OF PLANTS 
 
 poses and nature of these fruits, one should have 
 some entire ears which have been brought in with 
 the husk and are still attached to the stalk, or, at 
 least, a section of it. 
 
 I. The arrangement and protection of the fruits. 
 Examine the external characters of the ear and 
 its covering, and note : — 
 a. The silks, hanging in a reddish-brown tuft 
 
 from the tip. 
 h. The texture of the husks, and the manner 
 in which they cover the ear. Remove 
 one at a time, and compare the outer 
 and inner husks. 
 
 c. Take one of the " silks," and follow it 
 
 to its inner end. To what is it at- 
 tached ? 
 
 d. The great number of fruits arranged in 
 
 parallel rows on the central stalk or 
 '^ cob." Estimate the number of the 
 grains. 
 
 e. The attachment of the grain to the cob. 
 
 The scales. 
 /. The cob. Cut or break it across, and de- 
 scribe its structure. 
 
SEEDS AND FRUITS 167 
 
 II. The grains or seeds. 
 
 Place a number of seeds in moist earth ten days 
 
 before the observations are to be made, and 
 
 a few in water a day beforehand. Examine 
 
 the soaked seeds, and note : — 
 
 a. The forms, size and outward appearance. 
 
 Compare the two broader sides. 
 h. Remove the outer membrane which covers 
 the seed. This is composed not only of 
 the two seed-coats, but also of layers 
 from the walls of the ovary, which it 
 would be impossible to separate without 
 the use of methods which need the com- 
 pound microscope. 
 
 c. The seed is composed of two parts : the 
 
 embryo, which occupies the space under 
 the whitish area on one side, and the 
 mass of endosperm, or stored food. 
 
 d. Examine the endosperm, and test with a 
 
 drop of iodine. It is this portion of the 
 grain that is chiefly used for food by man. 
 
 III. The embryo. 
 
 Remove the entire embryo from a softened 
 grain, and note : — 
 
168 THE NATURE AND WORK OF PLANTS 
 
 a. Its general shape. Sketch. 
 
 b. The scutellum, or absorbing organ, the 
 
 part which lies under the embryo and 
 in contact with the endosperm. If ger- 
 minated seeds are examined, this organ 
 will be seen to have enlarged and taken 
 up some of the endosperm, as in the date 
 or cocoanut. It has the power of se- 
 creting digestive fluids, which dissolve 
 starch and convert it into sugar. The 
 action of this fluid on the endosperm 
 soon causes it to become soft, and then 
 milky fluid. 
 
 c. The young plantlet shows an unrolling 
 
 leaflet, a short stem, and a main root. 
 Describe the action of these organs in 
 germination. Note the formation of 
 young roots above the base of the main 
 roots. These are the stilt roots, which 
 are so prominent on the full-grown 
 plant (§ 29). 
 
 IV. Endurance of the seeds. 
 
 Put a number of sound grains into a covered 
 vessel full of water, set on the stove, and 
 
SEEDS AND FRUITS 1C9 
 
 allow the water to boil. Place an equal 
 number of grains on the cover of the ves- 
 sel, but where they will be dry. Plant 
 both lots of seeds in the soil, and note : — 
 
 a. The number that germinate. What do 
 
 you conclude as to the power of the 
 grain to resist extremes of heat? 
 
 Put a number of grains in a shallow 
 dish of water in the morning, and set 
 outside where they may freeze at night. 
 Place alongside these an equal number 
 in a dry dish. Now put both lots in 
 separate boxes of moist soil, keep in a 
 comfortable livmg room, and note : — 
 
 b. The number germinating. What do 3'ou 
 
 conclude as to the power of the grains 
 to resist cold ? 
 
 The capacity of the seed to endure 
 heat or cold is very great. The seed of 
 a plant is capable of undergoing much 
 greater extremes of climate than the 
 adult plant, which is largely due to the 
 fact that it contains very little water. 
 Thus a seed if kept dry may be exposed 
 to a heat which will boil water and still 
 
170 THE NATURE AND WORK OF PLANTS 
 
 germinate, but if actually put into boil- 
 ing water and permitted to absorb the 
 warm liquid, it will be killed. On the 
 other hand, seeds of many common 
 plants may be bathed in liquid hydro- 
 gen at a temperature of four hundred 
 and twenty degrees below freezing point 
 and still retain the power of germination. 
 
 V. The dissemination of the seeds. 
 
 a. Could dissemination take place by water 
 or wind ? 
 
 h. If you can observe a field of corn, note 
 whether any animals carry away the 
 grains or not, and if so what is done 
 with them. Are all of them destroyed ? 
 It would also be interesting to make 
 similar observations on the acorns of 
 the oaks. 
 
 Man has been an important factor in 
 the distribution of corn, and his method 
 of growing and treating it has resulted 
 in the development of new species and 
 „ varieties. It is cultivated over great 
 areas, and although the larger number 
 
SEEDS AND FRUITS 171 
 
 of the seeds produced annually are used 
 as food, yet enough are preserved to 
 perpetuate the species, so that this plant 
 is represented by many millions of in- 
 dividuals in regions where it would 
 have none if it were not for man. 
 Thus without the interference of man 
 corn could not grow and seed from year 
 to year in any place in northern United 
 States. 
 
 214. 77ie fruit of the dot-hur, Xanthium. — The 
 fruits of this plant, which is a relative of the sun- 
 flower, are very much different from those previously 
 examined, both in structure and action. The plant 
 is a weed, and it is more or less abundant over a 
 great part of the United States. The fruits may 
 be taken from the plant in August or September, 
 picked up from the ground or taken from the coats 
 of animals in late autumn. 
 
 I. External ajJj^earcmce of fruit. 
 
 Examine the clusters of four or five fruits, and 
 note their position on the plant as well as 
 the following features : — 
 a. The prongs at the apex, and the hooked 
 
172 THE NATURE AND WORK OF PLANTS 
 
 bristles over the remainder of the fruit. 
 Make a drawing, showing form and ar- 
 rangement of bristles. 
 h. Cut across the fruit, and note the struc- 
 ture of the outer walls which bear the 
 bristles, and that the fruit is two-seeded. 
 
 II. The seeds. 
 
 a. The seeds are unequal in size. 
 h. The seed-coats are distinct in texture and 
 color. Describe. 
 
 III. The emhryo. 
 
 a. The embryo seems to fill the entire seed. 
 The food is stored up in two oblong 
 oval leaflike bodies, the cotyledons, 
 which are whitish in color. 
 
 h. The 2^^umide, or young leaves, may be 
 found between the cotyledons and the 
 short main root below them. Draw 
 the embryo. 
 
 IV. Germination. 
 
 a. Examine twenty seeds which have lain in 
 moist soil for a month, and from each 
 fruit generally but one plantlet will 
 have grown. Take up the fruit which 
 
SEEDS AND FRUITS 173 
 
 is still attached to the single germi- 
 nated embryo. The other seed has not 
 shown any signs of growth. 
 h. Take a number of these fruits from which 
 one plantlet has sprung, and put them 
 in a pot and set out of doors for a 
 season. Many of them will be found 
 to germinate the second seed. 
 
 c. Examine the young plant, and note the 
 
 position and growth of the cotyledons. 
 What becomes of them? How does 
 the root develop? The single cotyle- 
 don of the species previously examined 
 did not come out of the seed-coats ; 
 what is the behavior in this instance ? 
 
 d. Strip the seeds of several fruits, being 
 
 careful not to injure them, and find 
 whether they will germinate alone. 
 
 215. Nature of fruits of Xanthium. — The fruits 
 of Xanthium are seen to be adapted for the dis- 
 semination of the seeds by becoming fastened or 
 entangled in the coats of animals, and thus are 
 carried long distances from the parent plant. In 
 the case of migratory animals this method might 
 
174 THE NATURE AND WORK OF PLANTS 
 
 carry them the length or breadth of a continent, 
 across wide seas, or over mountain ranges. 
 
 The Xanthium has an additional device not found 
 on any other known plant. This is the manner in 
 which the ^;a/re<i seeds germinate, one the first year 
 and the other the second. This method would enable 
 it to gain a foothold in places where it otherwise 
 might not. Thus, when the fruit is carried to a 
 field or dropped along the path of the animal to 
 which it has been attached, the coming of the 
 spring season sets one seed in action and a plant- 
 let is produced. This may survive and produce a 
 crop of fruits, in which case the species will easily 
 hold its own in this locality. On the other hand, 
 the young plant may be trampled to death by the 
 same animal which brought it to the place, it may 
 be overshadowed by other species which grow more 
 luxuriantly, or the watchful farmer may take this 
 opportunity to destroy one of the worst enemies of 
 his crops. The destruction of the first seedling 
 from any cause, however, still leaves the species 
 another chance to gain a foothold in this locality, 
 for at the beginning of the second season the other 
 seed germinates and begins the struggle for exist- 
 ence for the species all over again. 
 
SEEDS AND FEUITS 175 
 
 The fruit of the Xanthium then is not only fur- 
 nished with a device for securing transportation 
 from any animal that touches its fruits, but after 
 the fruits have reached a spot favorable for growth, 
 only half the seeds are germinated, the remainder 
 being held in reserve for a second attempt which 
 may be more successful than the first. Thus, if at 
 this moment every plant of this species were de- 
 stroyed, there would still remain the second seeds of 
 the fruits which have sent up but one plantlet and 
 kept the other in the form of a seed. 
 
 216. TJie apple. — The fruit of the apple offers 
 a most interesting study, not only on account of the 
 structure, but also because of the manner in which 
 it has succeeded in attracting the attention of ani- 
 mals, particularly man, and has thus secured dis- 
 semination over an immense area of the earth's 
 surface. During this process it has also undergone 
 great changes as a result of the methods of cultiva- 
 tion by which it has been grown. 
 
 In the examination of the flower of the apple it 
 was seen that the ovary was imbedded in a small 
 greenish capsule, and that the parts of the flower ap- 
 peared to stand on top of it (§ 202). All of the parts 
 
176 THE NATURE AND WOBK OF PLANTS 
 
 of a flower really spring from the end of the flower- 
 stalk, so that this young apple consists of the bases 
 of the petals, sepals, stamens, and pistils fused to- 
 gether. The fruit of the apple is thus composed 
 of portions derived from all of the organs of the 
 flower. Cut across a mature apple in the middle, 
 and note in the exact centre : — 
 
 a. The core. — It is seen to be joined directly to 
 the stem at the base of the apple, and terminates 
 at the other end in some small dried appendages, 
 which cannot be made out in a ripe apple. If a 
 half-grown specimen is secured fresh from a tree, it 
 will be seen that the five styles of the pistil are 
 attached to the core. Down in the centre of the 
 core will be found five small chambers containing 
 seeds; the pistil of this plant was therefore com- 
 pound, and each of the five styles furnished a pas- 
 sageway for pollen tubes to the egg-cells in the 
 chambers at its base. 
 
 Make out the 7nemhrane lining the seed cavities, 
 or cells. Examine the flesh of the apple. Note the 
 outer skin. It is often very strong and is covered 
 with a layer of wax. What is the difference between 
 the flesh of apples which may be kept for a long 
 time, and those which rot shortly after they ripen ? 
 
SEEDS AND FRUITS 177 
 
 The membrane which lines the cavity of the cells 
 containing the seed corresponds to the pod of a pea 
 m being the wall of the ovary, and the flesh is de- 
 rived from the calyx and perhaps a part of the stalk. 
 The calyx and stamens are seen adhering to the flesh 
 in half-grown fruits. 
 
 Examine the seed with respect to its coats and 
 methods of germination. 
 
 The fruit of the apple attracts animals by the 
 food which it offers them, and in the use of this 
 fruit the seeds would be carried some distance from 
 the parent tree. This method operated both with 
 regard to man and lower animals in earlier times. 
 Later, since man has developed the art of improving 
 or increasing its fruit-bearing capacity in order to 
 derive still more benefit from it, the apple has 
 had a very peculiar history. The edibility of its 
 fruit has still been the attractive feature, and this 
 has secured the wide dissemination of the apple, 
 not by the seeds which the fruit contains, but it has 
 induced man to propagate it by means of cuttings. 
 The cuttings are sometimes grown directly in the 
 soil, as in other forms discussed in a previous para- 
 graph. By a method of grafting, or causing a shoot 
 of one tree to adhere and grow to the body of 
 
178 THE NATURE AND WORE OF PLANTS 
 
 another, special varieties are propagated without 
 the use of seed. The forms developed in this 
 method are very widely different from the type of 
 the species, and when a seed of a fruit borne on 
 one of these grafted branches is planted, it produces 
 a tree which is unlike the characteristic branch from 
 which it sprung, and it is said not to " come true." 
 As a matter of fact the seedling does come true to 
 the species, but not to the cutting or grafted branch 
 from which it sprung. 
 
 217. The hean and ^jea. — Examine a flower of 
 the bean and pea. Note the characters of the dif- 
 ferent parts of the flower. Describe the number and 
 arrangement of the stamens and pistils. Is pollina- 
 tion aided by the wind or animals ? Follow the 
 development of the pistil. From what is the pod 
 derived ? Note the manner in which the pods open, 
 and the position of the seeds which fall upon the 
 ground. How far are they thrown from the parent 
 plant ? Do the pods open forcibly ? 
 
 Describe and draw the outward appearance and 
 form of the seeds. Note the number and character 
 of the coats. 
 
 A number of peas and beans should be placed in 
 
SEEDS AND FRUITS 179 
 
 tlie soil two weeks before the observations are to be 
 made, and a similar number in a tumbler with damp 
 blotting paper three or four days before. Dissect 
 one of each kind which has been treated in the 
 latter way. The seed is made up almost entirely 
 from two large swollen seed leaves or cotyledons, 
 which readily separate when the coats are removed. 
 At one side, holding the cotyledons together, may 
 be seen the young plant, consisting of the root, em- 
 hryonic stem, and the minute leaves, or plumule. To 
 what part are the cotyledons attached ? 
 
 If the seeds which Avere placed in the soil in 
 boxes or in the ground are now observed, the be- 
 havior of the cotyledons may be followed. Both 
 contain the reserve food for the young plant, and 
 yield it as needed. What position do the cotyle- 
 dons take in each case? How long do they endure, 
 and what is their fate ? Make drawings illustrating 
 the points made. 
 
 The development of the leaves also offers a point 
 of interest. Make drawings of the first, second, 
 and third leaves of the bean, and note the differ- 
 ence in their structure. Make drawings and note 
 form of the five leaves which appear first on the 
 stem of the pea. It will be seen in both instances 
 
180 THE NATURE AND WORK OF PLANTS 
 
 that the first leaf that appears is simple, the blade 
 not being divided or branched. In the bean it is 
 an active green leaf, but in the pea it is a small 
 three-pointed scale or bract which is not very 
 conspicuous and may be easily overlooked. The 
 second leaf will show greatest difference from the 
 first in the bean, and the third of that plant will 
 be very nearly the form seen on the adult stems. 
 The second leaf of the pea, however, is but little 
 more developed than the first, but the third, fourth, 
 and fifth show increased development. Perhaps not 
 until the sixth or seventh leaf is reached will you 
 find the characteristic leaf of the pea. The incom- 
 plete or simple leaves of seedlings are termed em- 
 bryonic leaves, and it is a theory of the botanist 
 that they represent forms used by the species in 
 earlier stages of its history, and these leaves are 
 the leaves of its ancestors, slightly changed of 
 course. Thus many thousands or millions of years 
 ago the group of plants from which beans have 
 sprung were furnished with simple leaves like those 
 shown just above the cotyledon. Later these plants 
 began to form lobes in the lamina, and finally it 
 was branched or divided as in the modern bean. 
 There may be still other stages between these, or 
 
SEEDS AND FRUITS 181 
 
 before any of them, which are lost. For while the 
 plant may repeat a part of its ancient history, we 
 cannot be quite sure that it has recounted all of 
 it. In fact, it would be almost impossible for it to 
 do so. In the instance of the pea, the bracts or 
 first leaves may be simply the bases of incomj^lete 
 organs and may not represent the lamina at all. 
 
IX. THE POWER OR ENERGY OF THE 
 PLANT 
 
 218. Enercjij in the jjlant. — In the preceding 
 paragraphs the plant has been shown to do a great 
 many kinds of work, and to use great force or 
 power in carrying out these processes. The push- 
 ing of roots through the soil, the movements of 
 these and other organs, the lifting of the food from 
 the soil to the top of the stems, the pumping of 
 the water from the roots to the leaves, — a distance 
 which may be as great as five hundred feet, — are 
 examples of external forms of work done by the 
 plant. The living plant is only a machine, and it 
 cannot originate or give rise to energy any more 
 than a steam engine may. The engine is simply 
 a device for using the energy released when fuel 
 is burned in its furnaces. This energy in the form 
 of heat converts water into steam, and it may be 
 conducted through pipes and made to act in a man- 
 ner convenient to the operator. 
 
 219. Sources of energy. — The plant receives en- 
 ergy from sunlight, and from the chemical com- 
 
 182 
 
THE POWER OR ENERGY OF THE PLANT 183 
 
 pounds which it absorbs from the soil, and also 
 makes use of the physical energy exhibited by cer- 
 tain substances. 
 
 220. Sunlight as a source of energy. — The por- 
 tion of sunlight absorbed by leaves is used as a 
 means of separating compounds in such manner 
 that the parts of these compounds will form new 
 and more powerful unions. It is as if one had two 
 magnets, to each of which was adhering a small bar 
 of iron. By the use of a small amount of force 
 the magnets and the iron may be separated, and 
 then the magnets will mutually attract each other 
 with greater force. Sunlight tears away some of 
 the oxygen united with the magnet hydrogen to 
 form water, and some of the oxygen united with 
 the magnet carbon in carbon dioxide, leaving the 
 carbon and hydrogen to rush together, forming a 
 stronger chemical union and carrying with them 
 a portion of the oxygen. 
 
 221. Chemical compounds as a source of energy. — • 
 Animals get all their energy from chemical com- 
 pounds used as food. The foods of the plant are 
 very simple compounds, but they gain some energy 
 in this manner. 
 
184 THE NATURE AND WORE OF PLANTS 
 
 222. Physical attraction as a source of energy. 
 — Compounds often exert an attraction for each 
 other, and the resulting union does not change the 
 composition of either of them. Thus sugar and 
 salt attract water, and will even draw it from the 
 air; but when sugar and water come together, they 
 form a solution, and the composition of neither is 
 disturbed. The water may be driven off and the 
 sugar will remain as before. Examples of this 
 were seen in the experiments illustrating the action 
 of the root-hair. 
 
 223. Release of energy. — After energy has been 
 acquired by the plant, it may be transformed or 
 released and made to do various kinds of work. 
 The principal method of releasing energy is the 
 same as that used in the steam engine, and con- 
 sists in oxidizing or huming the compounds which 
 contain it. 
 
 224. Respiration or hreathing. — The slow burn- 
 ing of material goes on almost constantly in all 
 living substance, and it is essentially the same kind 
 of a process in both plants and animals. It is most 
 rapid in growing tissues and slowest in resting seeds 
 and spores. It is still maintained, however, and it 
 
THE POWER OR ENERGY OF THE PLANT 185 
 
 is this slow burning up of the protoplasm which is 
 responsible for the death of old seeds. At extremely 
 low temperatures it ceases, as do all the activities 
 of protoplasm. Thus when seeds are placed in 
 liquid air at a temperature of nearly three hundred 
 degrees below zero, Fahrenheit, it can be stated 
 with certainty that breathing as well as all other 
 activities have ceased. 
 
 225. Changes in the air j^'i^oduced by breathing. — 
 The oxygen used in breathing is sometimes taken 
 from compounds in the plant, and then the burn= 
 ing is sometimes incomplete, and no external evi- 
 dence of it can be seen. In one form, however, 
 marked changes are made in the air. This may be 
 detected by the following experiment. Secure three 
 fruit jars and fill one half-full of peas which have 
 been soaked in water for a day, put the same 
 quantity of dried peas in the second, and allow 
 the third to remain empty. Cover tightly. A day 
 later prepare a small torch by fastening a section of 
 a candle an inch long to a piece of wire a foot long. 
 A bit of string soaked in oil will answer equally 
 well. Light the torch, remove the cover of the 
 empty jar, and lower the blaze into it. The flame 
 
186 THE NATUBE AND WORK OF PLANTS 
 
 remains unchanged. Repeat with the jar of dried 
 seeds. No effect is noticeable. Repeat with the ger- 
 minating seeds. The blaze is extinguished. Relight 
 and test again. The extinguishment of the blaze has 
 a double meaning. The oxygen of the air, which 
 is necessary to support the blaze, has been used by 
 the germinating seeds for their burning. In its 
 place is the carbon dioxide which has been produced, 
 which now forms one-fifth of the air in the jar. 
 
 The burning of the quiescent dry seeds is so slow 
 that it has not produced any change in the ah" about 
 them. The second and third jars show that it is not 
 the influence of the jar which extinguishes the blaze. 
 
 The above experiment may be performed with 
 mushrooms, flowers, or any portion of the living 
 plant which does not contain chlorophyl. Breath- 
 ing is carried on by all parts of the plant, but the 
 portions which contain chlorophyl take up the car- 
 bon dioxide thirty times faster than it is formed by 
 the same organ. Thus, if green plants were enclosed 
 in the jar the carbon dioxide would be quickly used, 
 and the amount of oxygen increased. 
 
 226. Plants by day and hy night. — During the 
 daytime the green plant takes up thirty times as 
 
THE POWER OR ENERGY OF THE PLANT 187 
 
 much carbon dioxide as it gives off, and throws off 
 thirty times as much oxygen as it uses. At night, 
 however, it burns and exhibits only the action of 
 the germinating seeds. This has led to a popular 
 belief that living plants in a sleeping room have an 
 unhealthful effect on the occupant because of the 
 carbon dioxide which they throw off. Such effects 
 are largely imaginary, because all the plants which 
 could be crowded into a bedroom would not give 
 off as much carbon dioxide as a single candle. 
 
 227. Relation of the living world and the atmos- 
 phere. — It is also a common impression that the 
 activities of plants and animals balance each other 
 in maintaining the composition of the atmosphere, 
 and it will be profitable to recall some of the 
 general facts bearing upon this question. 
 
 A single person throws about two pounds of 
 carbon dioxide into the atmosphere daily, and the 
 total product of the human race for twenty-four 
 hours is twenty-seven or twenty-eight hundred mill- 
 ion pounds. The breathing of the lower animals and 
 plants and the products of fires bring the total 
 amount of carbon dioxide produced daily by living 
 beings directly and indirectly to about six thousand 
 
188 TEE NATURE AND WORK OF PLANTS 
 
 million pounds. Fifty square yards of leaf surface 
 will take up as much carbon dioxide as may be 
 thrown off by a single person, and furnish as much 
 oxygen as he would need. When the immense area 
 of the leaves of all the plants in the world is con- 
 sidered, it is found at the extremest low estimate 
 that the vegetable world uses more than twice as 
 much carbon dioxide as may be produced by living 
 agencies, and gives off twice as much oxygen as 
 they consume. No appreciable change has ever 
 been found in the composition of the atmosphere 
 with respect to these gases, however, and it must 
 be concluded that other agencies are at work which 
 use these gases ; otherwise the air would be grow- 
 ing poorer in carbon dioxide and richer in oxygen. 
 It is found that changes are constantly going on 
 in the soil and in the rocks, which liberate and 
 take up these gases in quantities which make the 
 amounts used by living things seem very insignificant, 
 and that the waters of the sea form a vast store- 
 house for them. Then again the atmosphere con- 
 tains about eight thousand billions of pounds of 
 carbon dioxide, and if the activities of plants were 
 to cease entirely, it would be many hundreds of 
 years before the proportion of gases would be 
 
THE POWER OB ENERGY OF THE PLANT 189 
 
 altered sufficiently to be sensible to any other living 
 thing. 
 
 Furthermore, plants are capable of using nearly 
 two hundred times as much carbon dioxide as they 
 now get in the atmosphere, so that there is no 
 actual balance between plants and animals so far 
 as the atmosphere is concerned. 
 
 228. Energy of ^j/iT/s/caZ attraction. — It has 
 been seen that the attraction of sugar for water 
 results in pulling water into the plant containing 
 food. It is also known that this same action car- 
 ries fluids from one part of the body to another, 
 and serves especially in aiding to carry the current 
 of water from the roots to the leaves. It is this 
 power of attraction of one substance for another 
 which fills the cells with water, making them tense 
 and firm. The firmness of the cells filled with 
 water in this manner is all that holds up the soft 
 stems of herbaceous plants. When the water is 
 driven off by heat this work is no longer accom- 
 plished, and the stems wilt and fall over. Water 
 is attracted into the cells by certain substances, and 
 if substances with stronger attractive power are 
 placed outside the plant, the water will be with- 
 
190 THE NATURE AND WORK OF PLANTS 
 
 drawn from the cells, and the plant will become as 
 limp as if it were wilted in the sun. Cut off the 
 plump, rapidly growing shoots of any soft-bodied 
 plant and lay them in a deep dish which contains 
 water saturated with sugar or salt. Examine after 
 a few hours. The shoots will be found limp and 
 weak, and bend over when you attempt to hold 
 them upright by the basal parts of the stems. 
 
 229. Outward loork acco7n2)lished hy ^;/i?/s/crtZ 
 attraction. — When water is attracted into a cell 
 the cell expands with a force which may be equal 
 to twenty times the pressure of the atmosphere. 
 The expansion of the cells of a root will split 
 apart rocks and perform similar work. This may 
 be demonstrated as follows: Fill a narrow-necked 
 bottle of a capacity of four to eight ounces with 
 dried peas. Next pour in as much water as the 
 bottle will hold, and then, without admitting air, 
 invert the bottle, and set the mouth in a dish of 
 water. Examine a day or two later. The cells of 
 the seeds will have taken in so much water under 
 the attractive power of the substances which they 
 contain that they have expanded and burst the 
 walls of the bottle. 
 
X. RELATIONS OF PLANTS TO EACH 
 OTHER AND THEIR HABITAT 
 
 230. Societies and communities. — All living things 
 exist in the form of societies and communities, in 
 a manner which is fairly well illustrated by the 
 mode of life of the human family. Men attempt 
 to live in the places where they may most easily 
 obtain food, clothing, and shelter, and enjoy comfort. 
 Nearly every man devotes his energy to certain 
 kinds of work, and lives in a suitable house so far 
 as possible for him to do so. It may be readily seen 
 that the men devoted to one trade could not form a 
 community. Thus the tailors, tinners, blacksmiths, 
 carpenters, and merchants could not separately form 
 communities, for a community is made up of repre- 
 sentatives of each of these and many other kinds of 
 workers. A community comprises the people in a 
 town, village, city, or a region of the country occu- 
 pied by a village and outlying land, according to 
 the habits of the people. Generally some one trade 
 or group of workers occupies the most prominent 
 place in the community, and this causes it to be 
 
 191 
 
192 THE NATURE AND WORE OF PLANTS 
 
 spoken of as a farming community, a mining camp 
 or town, a manufacturing town or city, a fishing 
 village or shipping town, according to the kind of 
 work most prominent in its affairs. 
 
 231. Plant societies. — The plants of different 
 areas on the earth's surface are unlike in general 
 form, are made up of different species, and secure 
 the things essential to life in very different manners, 
 and constitute a comrriunity. The principal commu- 
 nities in northern United States are forests, mead- 
 ows, sivamj:) societies, j^otid societies, heach marshes, 
 thickets, heaths, moors, sand, and rock societies, beside 
 many others of more or less frequent occurrence. 
 The general aspect of a society in the landscape is 
 determined by its largest or most prominent member. 
 Thus, for instance, if the chief member is a tree, the 
 community will be a forest. Further, the forest goes 
 by the name of the most abundant tree, and there 
 are oak forests, beech, maple, and pine forests or 
 communities. In many cases communities have 
 taken on the names of the place in which they live, 
 as in swamp, rock, beach, and sand societies. 
 
 232. Foundations of society. — The things which 
 determine the character of any plant community 
 
RELATIONS OF PLANTS TO EACH OTHER 193 
 
 are, — the water siqjplij, tem^yerature of the soil and air, 
 jihysical and chemical jjrojjer^ties of the soil, winds, 
 and light. The length of time during which these 
 conditions have continued unchanged in any given 
 piece of land or country is also a very important 
 factor. 
 
 233. Communities change. — Communities are al- 
 ways in a state of being changed, and they may 
 disappear from any place and others may replace 
 them. A good example of this will be seen if a 
 marsh or pond is drained. During the existence of 
 the pond, water societies only could live there. The 
 mud left by the pond will allow societies of lower 
 plants to form a green coating over its surface. 
 After a time liverworts, mosses, and ferns may find 
 suita-ble conditions here. Later, when the mud has 
 dried and the soil becomes loose and loamy, llowering 
 plants will find a foothold, and if imdisturbed, young 
 trees may grow up, and thus the place once occupied 
 by a pond society will be the residence of a forest. 
 But even then the changes are not all past. The 
 action of the first kind of trees on the soil may fit 
 it for the growth of other trees, and the first forest 
 may be replaced by a different one. Similar move- 
 
194 THE NATURE AND WORK OF PLANTS 
 
 merits have been followed in the development of 
 humcan societies. The hunter and the pioneer first 
 occupy the soil or land, to be followed by the miner 
 and the farmer, and then by the manufacturing town 
 or the city. 
 
 234. Water and ^9?aw^s. — The plant is ex- 
 tremely sensitive about its supply of water. Not 
 only must it have a certain amount of rainfall each 
 year, but the rain must be given throughout the 
 whole year, instead of all at one time. The amount 
 capable of being retained by the soil and the salts 
 it contains are also of importance. The pond socie- 
 ties float in or on top of the water, or are submerged 
 beneath it. 
 
 235. Temperature and plants. — Each species 
 requires a certain number of warm days for its 
 development and can endure only certain low tem- 
 peratures. Thus our summers in the Middle states 
 are warm enough for the castor-oil plant out of doors, 
 but the low temperatures of winter kill it. The 
 warmth-retaining value of the soil is to be taken 
 into account in this connection. The surface of the 
 country is also a feature. In broken hilly regions 
 the cold air settles down in the valleys, making 
 
RELATIONS OF PLANTS TO EACH OTHER 195 
 
 them much colder than the near-by hill-tops, and 
 these valleys are much warmer in the daytime than 
 the hills. 
 
 236. TJie soil and plants. — The chemical char- 
 acter of the soil with respect to the kind and 
 amount of food it contains, and its physical qualities 
 due to its coarseness or fineness, and jDower to hold 
 water, as well as its heating properties, influence 
 the communities growing upon it. The principal 
 soils are rock, sand, lime, humus or loam, and clay. 
 Beside the soil itself, the coverings of snow, leaves, 
 or living 2^lants are of value to the community. 
 
 237. Light and ^9/a?i/Js. — Light is necessary for 
 all green plants, but some are able to make use of 
 rays of less intensity than others, and have altered 
 the structure of their entire bodies to suit this adapta- 
 tion. The species which can use the weaker light 
 usually stand under those that require the full blaze 
 of the sun, in the shadow of rocks, on northern 
 slopes, or if they are aquatic species they live at 
 some depth under the surface of the water. Along 
 a sea beach the area between high and low water 
 which is thus exposed to the full force of tlie suu 
 part of every day is inhabited by green, brown, and 
 
196 THE NATURE AND WORK OF PLANTS 
 
 red seaweeds. The top layer of water extending to 
 a depth of a hundred and fifty feet is inhabited by 
 red and some brown algae, and below this depth for 
 a short distance the red algge alone find suitable 
 conditions. Bacteria may live at depths of over half 
 a mile or in complete darkness, in the same manner 
 that mushrooms or other non-green species may live 
 in caves completely shut off from the light. 
 
 238. Wind and plants. — The wind affects the 
 character of the stems developed, and is a very im- 
 portant factor in carrying pollen from one flower to 
 another, disseminating seeds, spores, and other repro- 
 ductive bodies. Its general direction is an important 
 factor in determining; the rainfall also. 
 
 239. Forests. — The best idea of a community 
 may be gained from the study of one as it lives in an 
 undisturbed condition, and it will be most profitable 
 to make the first observations on the subject in a 
 forest, since the relations of its members are more 
 easily determined than m some others. 
 
 In order that the work upon this point should 
 have any great value it should be extended through- 
 out the greater part of a season, though many fea- 
 tures of interest may be made out in a single visit. 
 
RELATIONS OF PLANTS TO EACH OTHER 197 
 
 It will be found most convenient to select the most 
 accessible forest and make visits of several hours 
 each to it on several days, which may be a week or 
 a month apart. This may be done by using the 
 weekly holiday for excursions, which may also be 
 made the opportunity of collecting material for other 
 experiments, and for the observation of reproduction, 
 dissemination of seeds and iruits, action of leaves, 
 etc. It is indispensable that some member of the 
 party should be able to identify the common species 
 of plants found in the community, and it will be 
 highly profitable and necessary that all should use a 
 manual in taking the census of the flora. 
 
 On the first visit to the forest walk over its entire 
 area, or enough of it to gain a general idea of its 
 extent, the character of its surface, whether level or 
 hilly, the direction in which it slopes, the drainage, 
 streams, ponds, or lakes. It will be important to as- 
 certain whether the forest has been visited by fire or 
 damaged by grazing animals. Furthermore, notes 
 should be begun and carried throughout the observa- 
 tions upon the animals which inhabit or frequent the 
 forest, and their influence upon the distribution of 
 seeds or pollen. 
 
 Is the soil swampy, moist, or dry ? What is its 
 
198 THE NATURE AND WORK OF PLANTS 
 
 composition ? Is it chiefly sand, clay, or rock ? Is 
 the rock limestone, granite, or quartz ? Is the soil 
 covered with a layer of fallen leaves, or has this been 
 destroyed ? 
 
 It will next be of importance to determine the 
 trees which make up the larger members of the com- 
 munity. With regard to this point two kinds may be 
 distinguished : pure and mixed forests. A pure forest 
 shows but one kind and a mixed forest many kinds 
 of trees. What species is most abundant ? Are the 
 trees closely crowded together so as to completely 
 shade the ground, or are they wide apart, thus per- 
 mitting light to reach the ground and the growth of 
 many other plants ? Pure forests, made up of pines, 
 hemlocks, or beeches generally shade the ground so 
 completely as to make it impossible for undershrubs 
 to live. Oak, maple, and hickory forests are generally 
 open and have much underbrush. Make a map of the 
 forest, showing the facts in regard to the occurrence 
 of the different kinds of trees. The trees may be 
 evergreen, retaining the leaves throughout the winter, 
 or these may be cast in the autumn. 
 
 Find the seedlings or young specimens of the trees, 
 and note whether they have found a foothold in 
 shaded or suuny places. Find a place where a tree 
 
RELATIONS OF PLANTS TO EACH OTHER 199 
 
 or cluiiip of trees has been destroyed or died, and 
 note whether the young trees which are springing 
 up in their places are of the same species as the dead 
 ones. This will do much to indicate the ultimate 
 fate of the forest. If you find that the dead trees 
 are being replaced by the same kind, it would mean 
 that the condition of the forest would remain un- 
 changed; but if different ones are gaining a foothold 
 the entire character of the forest would be changed 
 in the course of time. If all of the dead trees are 
 replaced by a single species, it would indicate that 
 finally a pure forest of that species would occupy the 
 locality if undisturbed by man. 
 
 Find the seeds and fruits of the trees and deter- 
 mine the manner in which they are disseminated, 
 and their endurance of cold and drought. 
 
 If possible find isolated trees, and note the dis- 
 tance to which their seeds have been carried. 
 
 Do they germinate as soon as set free from the 
 parent, or do they lie quiescent until the following 
 season? Observe the manner of germination. 
 
 Traverse the entire margin of the forest, and 
 note whether it is spreading or not. Do you find 
 young seedlings outside the area occupied by the 
 taller trees? 
 
200 THE NATURE AND WORK OF PLANTS 
 
 Note the occurrence of shrubs and small hushes. 
 Are they found under trees or in openmgs or mar- 
 gins ? In an open or mixed forest there may be 
 a continuous layer of shrubs over the entire area, 
 while in close woods they can find suitable con- 
 ditions only in the openings. Plot the positions 
 of the shrubs and determine the species repre- 
 sented. 
 
 Climbers will be found in greater or less abun- 
 dance. Some of these will be attached to the 
 trunks of the tallest trees,' while others are sup- 
 ported by the shrubs and low bushes. 
 
 The carjjet, or layer of plants which cling to 
 the surface or rise only a short distance above it, 
 will vary greatly with the manner in which the 
 trees are associated. In close pure forests, like 
 the hemlock, the carpet will be sparse and almost 
 entirely lacking from the depths of the wooded 
 area. A few low-growing species may be found 
 in open places or clinging to exposed rocks or 
 hillocks. In this carpet will be found mosses, 
 ferns, liverworts, creeping and trailing vines and 
 shrubs, and herbaceous plants which form tufts or 
 rosettes of leaves which lie close to the surface, 
 like the sedges, some grasses, or the saxifrages. 
 
RELATIONS OF PLANTS TO EACH OTHER 201 
 
 The loose soil is inhabited by scores of species of 
 fungi, which send their long strands in every direc- 
 tion, and occasionally develop the sporophyte in 
 the form of stalked capsules, puff-balls, or um- 
 brella-shaped "toadstools" or "mushrooms," while 
 the soil is teeming with bacteria, which cause the 
 decay of the leaves. It would be most interest- 
 ing to compare the carpet of a swampy portion 
 of the forest with that of a slope or wooded hill. 
 
 240. Relations of members of the forest. — The 
 relations of the members of the forest are most 
 close and intimate. A disturbance of one is likely 
 to influence all the others. Thus the leaves and 
 twigs from the trees form a light layer of loose soil 
 or humus necessary for the growth of mosses and 
 ferns, and the freshly fallen layer covers over the 
 members of the carpet each autumn with a blanket 
 which protects them from the extremes of the winter. 
 On the other hand, the destruction of the forest and 
 the loose soil by fire, or the action of grazing animals, 
 would result in injuries to the trees. 
 
 241. Time of blooming. — It needs but the most 
 casual acquaintance with plants to know that they do 
 not all bloom and ripen seeds at the same time of the 
 
202 THE NATURE AND WORK OF PLANTS 
 
 year. And it may be recalled that after the opening 
 of the growing season in spring there is a constant 
 succession of flowers throughout the summer. This 
 is not an accidental occurrence. Each species tends 
 to bloom and mature its seeds at a time when it may 
 do so to the best advantage and with the least com- 
 petition. Without going into all the points involved, 
 it is to be seen that if all the plants which need 
 insects to carry their pollen were to bloom at the 
 same time, the supply of honey they offer could not 
 secure the attention of the insects to more than 
 a few individuals of each species. As it is, how- 
 ever, every species secures a share of work of the 
 insects in cross-pollination, since only a few species 
 offer honey at the same time, and the seeds are 
 also disseminated with less competition. If all 
 the crops of a farmer were to be harvested at 
 the same time, they could neither be cared for nor 
 shipped properly. 
 
 242. Seasonal activiUj. — It must not be sup- 
 posed that the activity of the members of the forest 
 community is confined to the season in which flowers 
 appear. If a close examination of the community 
 is made in February or March, it will be found that 
 
RELATIONS OF PLANTS TO EACH OTUER 203 
 
 many of the mosses have developed the sporophytes 
 with their conspicuous capsules while the soil is still 
 frozen. The closely lying rosettes and evergreen 
 leaves have taken advantage of every sunny day, 
 and the flowering shoots will spring up into the air 
 on the earliest approach of spring. One species, a 
 shrub, the witch-hazel, blooms after its leaves have 
 fallen in October and November, and ripens its seeds 
 the next summer. Make note of the species of 
 all parts of the forest which bloom in the early 
 part of the spring, during a period of a month. 
 Some kinds will be found which form flowers be- 
 fore the leaves are up out of the ground, or are 
 unfolded from the buds. The first period should 
 cover all the time until the leaves of the trees 
 have appeared. 
 
 Make similar note of the species which bloom 
 before the opening of summer, or June 1st. What 
 are the earliest species to mature seeds and drop 
 them to the ground ? Do these seeds germinate at 
 once, or lie dormant until the next year? 
 
 Keep one or two species under constant observa- 
 tion, and determine the length of time between the 
 beginning of growth and the maturation of the 
 seeds and their germination. 
 
204 THE NATURE AND WORK OF PLANTS 
 
 It will be of equally great interest to follow the 
 activities of the forest members through early sum- 
 mer, midsummer, late summer, autumn, and late 
 autumn, until the closing of the season. 
 
 243. Families and species in the community. — 
 The work outlined in the previous pages should en- 
 able the student to make a census of the families 
 and species which make up the community. This 
 should be done in connection with the study of 
 the various elements in the forest. The student 
 should provide himself with a manual of the flora 
 of the region in which he is located, and make 
 himself familiar with the use of it so that he can 
 identify the majority of the species met with. The 
 study of the forest, enables one to group plants ac- 
 cording to habit and place in the community, but 
 the study of the flora gives a classification accord- 
 ing to relationship and descent. 
 
 Bring together specimens of species belonging to 
 the same genus, or family, and note their differences 
 and similarities in appearance. 
 
 Compare individuals of the same species w^hich 
 live in different kinds of soil, or in more or 
 less light. If possible, compare a swamp forest 
 
RELATIONS OF PLANTS TO EACH OTHER 205 
 
 with an upland forest in all the above particu- 
 lars. 
 
 244. 3feadoivs. — Natural meadows will not be 
 easy to find in the regions accessible to most readers 
 of this book. All have been mowed, or pastured 
 by grazing animals to such extent that the origi- 
 nal arrangement of the various members of the 
 community has been very much disturbed. Noth- 
 ing makes this more apparent than to find a 
 meadow that has been allowed to run to weeds. 
 This does not mean that the meadow returns to 
 its natural state. But, as soon as man ceases to 
 protect the plants he wishes to cultivate and to re- 
 new them by additions of seed brought from else- 
 where, they come into competition with vigorously 
 growing species which overtop them and partially 
 crowd them out, resulting in a new meadow. It 
 may be seen that the chief members in a meadow 
 are low grasses, clovers, small creepers, a few stray 
 mosses and liverworts, and a large number of peren- 
 nial herbs which form rosettes of leaves on the sur- 
 face and send up tall flowering stalks, like the 
 thistle, ironweed, mullein, joe-pye, and many others. 
 Perhaps the most natural meadows will be offered 
 
206 THE NATURE AND WORK OF PLANTS 
 
 by the open spaces in woodlands. Observe a spot 
 of this character, and note whether the young trees 
 from the forest are taking possession or not. 
 
 245. Hock societies. — Find a set of cliffs or 
 exposed ridge of rocks, and note the character of 
 the vegetation that finds a foothold there. It will 
 be seen that the distribution of the rock plants is 
 limited quite exactly by the extent of the stone on 
 which they grow. This is perhaps the most strik- 
 ing feature about these communities. Forests may 
 cover many square miles in extent, but rock socie- 
 ties usually extend over a few square yards only. 
 Still another feature will be brought out in a com- 
 parison of the rock society and the forest ; the thou- 
 sands of individuals in the forest crowd each other 
 fiercely for space in which to live, while the mem- 
 bers of the rock societies are scattered about over the 
 hard surface, finding a foothold where they may in 
 any convenient crevice or roughened area. Observe 
 a rock society throughout a portion of the season, 
 and make a census of its members. The number of 
 seed plants will be small. Ferns will probably be 
 represented, the mosses will form clumps or coat- 
 ings on moist portions of the rock, some liverworts 
 
RELATIONS OF PLANTS TO EACH OTHER 207 
 
 will be present; but the plant most at home in 
 such places is a flat-crusted one, of various shades 
 of greenish-brown, which lies flat on the surface, 
 growing vigorously in the wet seasons, and shrink- 
 ing to a hard brittle mass in dry weather. These 
 are the lichens, and other members of this group 
 sheathe the trunks of trees in the forest. Com- 
 pare the species found on different slopes of the 
 rock. 
 
 246. Fond societies. — Pond societies live in al- 
 most all waters except those of lakes and streams 
 polluted by the sewage of cities. The constitution 
 of such societies may be best studied in a pond, lake, 
 or sluggish stream, and a boat wdll be a useful 
 adjunct for the exploration of depths which cannot 
 be reached by wading. The soil above high water 
 will be very moist, offering suitable conditions for 
 a belt of cat-tails, then one of flowering plants, wil- 
 lows, and small shrubs, and back of these the trees 
 of a forest. 
 
 On the first visit to the place chosen for study, 
 note the extreme height to which the water rises, 
 and examine first the plants growing between the 
 high-water mark and the edge of the water. Identify 
 
208 THE NATURE AND WORK OF PLANTS 
 
 them, and note their habits of growth and repro- 
 duction. How are their seeds disseminated ? 
 
 Two main classes of plants will be found in the 
 water : one, which anchors to the bottom, entirely 
 submerged or partly floating, and another which 
 floats freely on the surface. In the first class will 
 be found many algae, which coat the stones at the 
 bottom of the shallow places, and pond-weeds, water- 
 lilies, arrow-leaf. Determine the form in which 
 these species live through the winter. Observe 
 the action of the flower stalk of the water arum. 
 How are the seeds of these plants spread from place 
 to place? 
 
 One of the members of this group, Vallisneria, lives 
 entirely underneath the surface, sending its pistillate 
 flowers up to the surface, at the end of long stalks, 
 while those containing stamens only, break off and 
 float. After the pistils have received the pollen, 
 the maturing seed-pods are drawn down under the 
 water by the action of the stalk, which assumes the 
 form of a corkscrew. Similar action is exhibited by 
 the water hyacinth, which roots in the mud in 
 shallow water or floats about in colonies. When 
 the seeds are formed, the stalks bend over, thrusting 
 the pods under the water. 
 
RELATIONS OF PLANTS TO EACH OTHER 209 
 
 Note the species floating on the surface. Among 
 these may be found the minute duckweeds, which 
 look like small leaves, and are of such size that 
 several of them may be laid side by side on the 
 thumb nail. The leafiike body represents both 
 leaves and stems, while but one slender root is 
 present that trails down in the water and serves as 
 a keel to prevent the upsetting of the leaf (§31). A 
 vivid coloring may be seen on the lower side of these 
 and other floating aquatic organs. In places the sur- 
 face may be taken up by numerous specimens of 
 the bladderwort with their curiously pouched leaves 
 full of minute entrapped animals. In quiet pools, 
 free from the action of currents, the surface will be 
 covered by heavy masses of a greenish scum, which 
 has a greasy feel when held between the fingers. 
 This is a very widely distributed alga, Spirogyra, 
 and the masses are composed of long threads made 
 up of cylindrical cells placed end to end. What 
 becomes of all these floating members of the com- 
 munity in the winter time ? How do they reappear 
 in the spring? 
 
 247. Locations occiqned by members of different 
 kinds of communities. — Low-lying areas may be 
 
210 THE NATURE AND WORK OF PLANTS 
 
 found in land which is not well drained that support 
 groups of members from two different kinds of com- 
 munities. This is to' be seen in places covered with 
 water by the spring floods, which last until early 
 summer. During this time the only species living in 
 the place are aquatic, both floating and rooting. 
 With the advance of summer the water evaporates, 
 leaving the soil dry and suitable for some of the 
 rapidly growing members of swamp or meadow 
 societies. A few species of algae, as well as some 
 of the seed plants, are so elastic in their habits that 
 they grow under both conditions. Thus the alga, 
 green velt (Vaucheria), may float or rest on moist soil 
 with equal facility. Species which cannot adapt 
 themselves in this manner live through the unfavora- 
 ble period in the form of seeds, tubers, or corms. 
 The continuation of either the floods by artificial or 
 natural dams, or the complete drainage of the area, 
 will result in the extinction of the members of the 
 group least adapted to withstand the change. 
 
 248. Extermination of a forest. — Find a piece of 
 woodland from which the trees have been recently 
 cut, and note the changes ensuing among the other 
 members of the community. 
 
RELATIONS OF PLANTS TO EACH OTHER 211 
 
 249. Fields. — Examine a cultivated field, and 
 note the kinds or species which exist there with the 
 crop plants. Do they belong to meadows, forests, 
 or swamps ? 
 
 250. Course of further study. — The work followed 
 in this book will give a general idea of the mode 
 of life and purposes of the plant world. It will 
 next be in order for the student to examine the 
 structure and development of representative types 
 of the great groups in which plants are divided, 
 — algse, fungi, liverworts, mosses, ferns, and seed 
 plants, — in order to comprehend their descent and 
 relationship, and the general laws by which plants 
 adapt their bodies to their environment. 
 
INDEX 
 
 Absorbing organ, 160, 163, 164. 
 Absorption, 21, 24, 26, 60, 51, 
 62. 
 
 of light, 63. 
 Acer, 4, 5. 
 Acids, 13, 18, 19. 
 Adam and Eve, 130. 
 Aerial roots, 44. 
 Air, composition of, 57. 
 
 changes in, by plants, 185, 186. 
 Algfe, 14, 52, 53, 208, 209. 
 Alkaloids, 19. 
 Allium, 135. 
 Amaranth, 59. 
 Anchorage, 24. 
 Annual rings, 108, 113. 
 Annuals, 113, 114. 
 Antimony, 17. 
 
 Apple, 67, 90, 117, 146, 175-178. 
 Argon, 57. 
 Arisaema, 27. 
 Arrow-leaf, 208. 
 Arsenic, 17. 
 Ascent of sap, 104, 107. 
 Ash, 10, 11, 15, 16. 
 Assimilation, 21. 
 Autumnal colors, 67, 68. 
 Autumnal leaf fall, 86. 
 Axis, main, 93. 
 
 Bacteria, 37, 52, 53, 76, 137, 201. 
 
 Ballast roots, 30. 
 
 Balsam apple, 120. 
 
 Bananas, 85. 
 
 Bark, 110, 111. 
 
 Bast. 98. 
 
 Bean, 36, 39, 40, 49, 56, 75, 109, 
 
 112, 148, 217. 
 Beech, 4, 29, 96, 133. 
 Beet, 19, 48, 69. 
 Begonia, 54, 107, 132. 
 Biennials, 113, 114. 
 Birch, 67. 
 
 Bladderwort, 66, 78, 79, 119, 209. 
 Bleeding, 105. 
 Bloom, 84. 
 Bracts, 95. 
 
 Breathing, 21, 184, 185. 
 Bristles, 122, 172. 
 Bromine, 16. 
 Buds, 49, 66, 94, 115-119, 121, 132, 
 
 133. 
 Bulbs, 121, 133, 135. 
 Bulbils, 133, 134, 135. 
 Bulblets, 134-136. 
 
 Cabbage, 84, 90. 
 Cactus, 1, 123. 
 Calcium, 16. 
 Calcium phosphate, 18. 
 Calla, 27, 28, 102, 121. 
 Canna, 70. 
 Carbon, 16, 18, 61. 
 Carbonic acid, 37, 57, 61, 64, IBS- 
 IBS, 186, 187, 188, 189. 
 Carrot, 11, 35. 
 Castor-oil plant, 194. 
 Cat-tail, 207. 
 Cellulose, 18. 
 Charcoal, 10, 11. 
 Cheat, 7. 
 Cherry, 5, 133. 
 
 213 
 
214 
 
 INDEX 
 
 Chess, 7. 
 
 Chestnut, 95, 96, 101. 
 Chlorine, 16, 18. 
 
 Chlorophyl, 58, 59, 60, 61, 62, 63, 
 64, 67, 69, 70, 76, 77, 144, 
 183. 
 Circular movement, 112. 
 Climbing roots, 28. 
 Clot-bur, 171-175. 
 Clover, 41, 205. 
 Club-mosses, 136. 
 Cob, 166. 
 Cockscomb, 159. 
 Cocoanut, 155-162. 
 Cocos nucifera, 155-162. 
 Cold, influence of, 89-92. 
 Cold-air drainage, 90. 
 Coleus, 15, 69, 70, 90, 132. 
 Collenchyma, 98. 
 Colors, 58-71, 120. 
 Columnar roots, 29. 
 Communities, 190-201. 
 Compass plants, 75, 76. 
 Composition of plants, 8-11. 
 Compounds in plants, 18. 
 
 of soil 30, 31. 
 
 of air, 57. 
 Conacephalus, 51, 55, 136. 
 Contact, influence upon roots, 43. 
 
 upon tendrils, 126. 
 Copper, 17. 
 Corallorhiza, 48. 
 Coral-root, 48, 77. 
 Core, 176. 
 Corn, 15, 99, 100, 111, 121, 155, 165- 
 
 171. 
 Corpse plant, 47. 
 Cotyledon, 160, 163, 164, 172, 173, 
 
 179, 180. 
 Cross-pollination, 202. 
 Cuscuta, 45. 
 Cuticle, 71, 84. 
 Cuttings, 1,32, 133. 
 Cystopteris, 136. 
 
 Darwin, 43. 
 
 Date, 162-165. 
 
 Dew, 85, 106, 107. 
 
 Dewberry, 137. 
 
 Digestion, 77. 
 
 Digestive fluid, 79. 
 
 Dissemination, 138, 149, 150, 151, 
 
 170, 177. 
 Distribution, 130. g, 
 
 Disuse, effects of, 48, 76, 77. 
 Division, 136, 137. 
 Dodder, 45-47. 
 Duckweed, 30, 209, 
 
 Egg, 132, 1.39, 149, 152, 153. 
 
 Elements in plants, 16, 17. 
 
 Elms, 4, 5, 41, 96. 
 
 Embryo, 159, 160, 167, 172, 178, 179. 
 
 Embryo sac, 152, 153. 
 
 Embryonic tissue, 96, 108, 115, 116. 
 
 Endosperm, 159, 167, 168. 
 
 Endurance of seeds, 168-170. 
 
 Energy of the plant, 182-190. 
 
 Euzym, 160, 168. 
 
 Epidermis, 27, 156. 
 
 Epsom salts, 18. 
 
 Equisetum, 13. 
 
 Evergreens, 87. 
 
 Extinction of species, 131. 
 
 Families, 24. 
 
 Ferns, 1, 4, 50, 80, 1,36, 139, 140, 
 
 141, 145, 146, 193, 200. 
 Fertilization, 151, 152. 
 Ficus, 29. 
 
 Fixation, 24-29, 50-53. 
 Flower, structure of, 146-148. 
 Food, 18. 
 
 Food-formation, 57, 58, 61, 80. 
 Forcing, 121, 122. 
 Forests, 196-204. 
 Foundations of society, 192. 
 Freezing, 89-92. 
 Frost, 89-92. 
 
INDEX 
 
 215 
 
 Fruits, 67, 60, 155. 
 Functions, 21, 22, 23. 
 
 of roots, 24. 
 
 of leaves, 58. 
 
 of stems, 93, 96. 
 Fungi, 47, 48, 77, 104, 111. 
 
 Gametes, 14^-144. 
 Gametophyte, 143-145. 
 Gas, 120. 
 
 Gases used by plants, 57. 
 Gemm£e, 138. 
 Generations, 7, 141-145. 
 Georgia oak, 130. 
 Geotropism, of roots, 4, 38, 39. 
 
 of leaves, 74. 
 
 of stems, 74. 
 Girdling, 103, 104. 
 Glands, 79. 
 Gleditschia, 123. 
 Grafting, 177, 178. 
 Grape, 95, 105. 
 
 Gravity, influence upon roots, 39, 
 40. 
 
 upon leaves, 74. 
 
 upon stems, 128, 129. 
 Growth of roots, 49. 
 
 in darkness, 03, 65, 122. 
 
 of leaves, 87. 
 
 of stems, 108, 109, 111. 
 Gum arable, 44. 
 
 Hairs, 71, 84. 
 Heliotropism, 73. 
 Hemlock, 198, 200. 
 Hibernacula, 119, 120. 
 Hickory, 110, 198. 
 Holdfast, 20, 153. 
 Honey, 78, 202. 
 Honey locust, 123. 
 Hop, 126. 
 
 Horse-chestnut, 86. 
 Horse radish, 133. 
 Humus, 37, 38. 
 
 Hyacinth, 25, 28, 121. 
 Hyacinthus, 27. 
 Hydrogen, 16, 18, 64, 183. 
 
 Indian pipe, 47, 77. 
 Insects, 161, 152. 
 Iodine, 16, 19, 167. 
 Ipomea, 49. 
 Iris, 56. 
 Iron, 16. 
 
 Iron chloride, 18. 
 Ironweed, 205. 
 Ivy, 65, 86. 
 
 Jack-in-the-pulpit, 27, 121, 123, 140. 
 
 Lamina, 54, 72, 73, 81, 85, 86. 
 
 Laminaria, 26. 
 
 Larkspur, 95, 148. 
 
 Leaf mosaic, 72. 
 
 Leaf traces, 95. 
 
 Leaves, 12, 54-92, 123, 179, 180. 
 
 Lemna, 30. 
 
 Lichens, 207. 
 
 Life, length of, 112, 113, 114, 115, 
 
 131, 155. 
 Light, influence upon roots, 40. 
 
 upon chlorophyl, 01-63. 
 
 relation to plant, 61, 195, 196. 
 Lily, 135, 148. 
 Line, 14, 16. 
 Liquid air, 185. 
 Liquid hydrogen, 185. 
 Liverworts, 50, 80, 136, 193, 200. 
 Loosestrife, 135. 
 Lunularia, 138. 
 
 Maize, 165-172. 
 
 Mangrove, 29. 
 
 Man of the earth, 49. 
 
 Maple, 3, 4, 6, 19, 68, 81, 86, 95, 
 
 96, 101, 105, 198. 
 Marchantia, 51, 55, 136, 138. 
 Meadow garlic, 135. 
 Meadows, 204. 
 
216 
 
 INDEX 
 
 Melon, 90. 
 Mesophyl, 55? 82. 
 Mlcrampelis, 126. 
 Midrib, 55. 
 
 Mineral coatings, 12-14. 
 Mint, 94, 95, 99, 100. 
 Mistletoe, 45. 
 Moisture, 154. 
 
 influence upon roots, 40. 
 Monotropa, 47. 
 Morning glory, 112, 126. 
 Mosses, 4, 7, 50, 80, 143, 193, 200, 
 
 203, 205. 
 Moulds, 76, 77. 
 Movements, of roots, 38-43. 
 
 of leaves, 73-75. 
 
 of stems, 74, 112. 
 
 sleep, 85. 
 Mullein, 85. 
 Mushrooms, 51, 52, 76, 77, 186, 
 
 201. 
 Mycelium, 52. 
 Mycorrhizas, 47, 48, 104. 
 
 Naked buds, 116. 
 Narcissus, 63, 112. 
 Nerves, 55. 
 
 Nitrogen, 16, 57, 61, 64. 
 Nodding movement, 112. 
 Nodes, 49, 94. 
 
 Oaks, 4, 68, 95, 110, 198. 
 Offsets, 21, 133. 
 Oil, 19, 154. 
 Onion, 121. 
 Orchid, 48. 
 Organs, 22, 23. 
 Ovary, 148, 158. 
 
 Oxygen, 16, 18, 57, 61, 64, 152, 183. 
 185, 186, 187, 188, 189. 
 
 Paired seeds, 172-174. 
 Palm, 29, 111, 156, 162, 
 
 Pansies, 85. 
 
 Parasites, 45, 77. 
 
 Parasitic roots, 45. 
 
 Passion flower, 126. 
 
 Path of sap, 103. 
 
 Pea, 39, 49, 56, 75, 178, 186, 190. 
 
 Peach, 67, 90. 
 
 Pelargonium, 116. 
 
 Peony, 67. 
 
 Perennials, 156. 
 
 Petals, 85, 147. 
 
 Petiole, 64, 72, 78, 81, 101. 
 
 Phosphorus, 16. 
 
 Pine, 4, 87. 
 
 Pine sap, 77. 
 
 Pistil, 148. 
 
 Pitchered leaves, 77, 78. 
 
 Pitcher plant, 78. 
 
 Pith, 90, 98, 167. 
 
 Plaster of Paris, 18. 
 
 Plum, 67. 
 
 Plumule, 161, 172, 179. 
 
 Poison ivy, 123, 124. 
 
 Pollen, 147-152. 
 
 Pollination, 149-151. 
 
 Polypody, 130. 
 
 Pond-scum, 4, 53, 80, 120. 
 
 Pond-weed, 14, 119, 208. 
 
 Poplar, 4, 81, 110, 133. 
 
 Position of leaves, 72, 73. 
 
 Potamogeton, 14. 
 
 Potassium, 16. 
 
 Pressure, by growing roots, 42. 
 
 by expanding cells, 190. 
 Primula, 85. 
 Protection, of roots, 43. 
 
 of leaves and stems, 122, 123. 
 Protein, 18. 
 Protoplasm, 1, 2, 3. 
 Puff-balls, 201. 
 Pumpkin, 126. 
 Purposes of plants, 3. 
 Putty root, 130. 
 
 Quercus Georgiana, 130. 
 
INDEX 
 
 217 
 
 Radish, 32, 41. 
 Raspberry, 137.' 
 Red color, 65-70. 
 Red maple, 5, 6. 
 Reproduction, 131-137. 
 Respiration, 184, 185. 
 Rliacliis, 56. 
 Rhizoids, 50, 141. 
 Rhubarb, 65, 102. 
 Rock societies, 206. 
 Root-cap, 42, 43. 
 Root-hairs, 31-36, 89. 
 Roots, 24-53. 
 Runners, 21, 137. 
 
 Salix, 15. 
 
 Salt, 18, 157. 
 
 Saprophytes, 77. 
 
 Sarracenia, 78. 
 
 Saxifrage, 200. 
 
 Scaly buds, 116. 
 
 Scouring rush, 13, 
 
 Scutellum, 168. 
 
 Seaweeds, 26. 
 
 Seed-coats, 158, 159, 167, 172, 177. 
 
 Seeds, 21, 131, 154-181. 
 
 Sensitiveness, of roots, 36-43. 
 
 of stems, 127-129. 
 
 of tendrils, 126, 127. 
 Shellac, 44. 
 Shrinkage, of leaves, 12. 
 
 of roots, 27. 
 Silicon, 13, 16, 123. 
 Silks, 166. 
 
 Sleeping buds, 118, 119. 
 Slime moulds, 2. 
 Smilax, 171. 
 Societies, 191-201. 
 Sodium, 16, 17, 18. 
 Soil, composition of, 30, 31. 
 Sorghum, 19. 
 Species, 6. 
 
 Spectrum of chlorophyl, 60. 
 Spines, 122. 
 
 Spirogyra, 53, 209. 
 
 Spongy layer, 45. 
 
 Spores, 21, 52, 131, 139, 140, 141, 
 
 142, 145, 149, 184. 
 Sporophyte, 142-146. 
 Spring beauty, 148. 
 Squash, 26, 126. 
 Starch, 19, 154. 
 Stems, 93-129. 
 Stigma, 147. 
 Stilt roots, 29. 
 Stinging hairs, 122. 
 Stolons, 137. 
 Stomata, 55, 82. 
 Storage in roots, 48. 
 Strawberries, 90, 137, 138. 
 Struggle for existence, 124, 125. 
 Styles, 147. 
 
 Sugar, 18, 19, 35, 36, 65; 66, 106. 
 Sugar maple, 4, 5, 6, 154, 184. 
 Sulphur, 16. 
 Sumach, 56, 58. 
 Sunflower, 12, 24, 26, 33, 100, 109, 
 
 131. 
 Sweet potato, 132, 133. 
 Sycamore, 4, 110. 
 
 Tannins, 19. 
 
 Temperature, 89-92, 154, 195. 
 
 Tendrils, 126, 127. 
 
 Thallus, 128, 197. 
 
 Thistle, 1, 123, 205. 
 
 Thorns, 122. 
 
 Tissues, 22, 23. 
 
 Toadstools, 51, 201. 
 
 Tobacco, 90. 
 
 Tomato, 25, 34, 40, 45, 67, 83, 96, 
 
 103. 
 Touch-me-not, 102. 
 Transplanting, 89. 
 Transpiration, 81-85, 88, 89. 
 Tubers, 133, 134. 
 Tulip tree, 68. 
 Turnip, 11. 
 
218 
 
 INDEX 
 
 Utricularia, 66, 78. 
 
 Vallisneria, 208. 
 Vaucheria, 210. 
 Vegetative reproduction, 132, 133, 
 
 139. 
 Velvety surfaces, 85. 
 Violets, 4, 5, 6, 85. 
 Virginia creeper, 66. 
 
 Walnut, 4. 
 
 Water cultures, 15. 
 
 Water hyacinth, 30, 43, 208. 
 
 Water, in plants, 10. 
 
 in leaves, 81. 
 
 in protoplasm, 90. 
 
 Water transpired, 82, 83, 84, 85. 
 
 Water lily, 120, 20ar. 
 
 Wax, 84, 176. 
 
 Weeds, 125. 
 
 Wheat, 7, 155. 
 
 White surfaces, 61. 
 
 Wild garlic, 135. 
 
 Wild onion, 135. 
 
 Willow, 15, 41, 55, 132, 207. 
 
 Wilting, 83, 34, 88, 97. 
 
 Wind, 150, 196. 
 
 Winter buds, 119, 120. 
 
 Witch-hazel, 203. 
 
 Wood, 98, 99. 
 
 Xanthium, 171-175. 
 
 fMPmT muBX 
 n. C SiaU College 
 
LESSONS WITH PLANTS 
 
 Suggestions for Seeing and Interpreting Some of the Common 
 Forms of Vegetation 
 
 By L. H. BAILEY 
 
 Professor of Horticulture in the Cornell University 
 
 With Delineations from Nature by W. S. HOLDSWORTH, of the 
 University of Michigan 
 
 523 pages. 446 illustrations. i2mo. Cloth. $1.10, net 
 
 There are two ways of looking at nature. The old way, which you have 
 found so unsatisfactory, was to classify everything - to consider leaves, roots, 
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 for himself. 
 
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 Professor V. M. Spalding, University of Michigan. 
 
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 subject, and to serve as a helpful and reliable guide to young students of 
 plant life. It will, I think, fill an important place in secondary schools, and 
 comes at an opportune time when helps of this kind are needed and eagerly 
 sought." 
 
 THE MACMILLAN COMPANY 
 
 NEW YORK BOSTON CHICAGO SAN FRANCISCO 
 
LABORATORY PRACTICE FOR 
 BEGINNERS IN BOTANY 
 
 WILLIAM A. 5ETCHELL, Ph.D. 
 
 Professor of Botany in the University of California 
 
 i2mo. 199 pages. 90 cents, net 
 
 INDORSEMENTS 
 
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 NEW YORK BOSTON CHICAGO SAN FRANCISCO