AMERICAN SCIENCE SERIES BOTANY HIGH SCHOOLS AND COLLEGES. BY CHAELBS E. BESSEY, M.Sc., PH.D., I'ROKESSOK OP BOTANY IN THK IOWA AGRICULTURAL COLLEGE AND LATE LECTURER IN THE UNIVERSITY OF CALIFORNIA. THIRD EDITION REVISED. NEW YORK HENRY HOLT AND COMPANY 1883 Copyright, 1880, BY HEKUY HOLT & Co. Presswork of DANIEL G. F. CLASS, 17&19Ko8cSt.,N.Y. : PREFACE. THIS book is designed to serve as an Introduction to the Study of Plants. It does not profess to give ik complete account of the Vegetable Kingdom, but only such an outline as will best subserve the pur- poses of the work. In its preparation there have been kept in view the wants of the large number, in the schools and out, who wish to obtain, as a branch of a liberal cul- ture, a general knowledge of the structure of plants, with some idea as to their classification into the larger divisions and subdivisions of the Vegetable Kingdom. For this class of students and general readers, what is here given will in most cases be amply sufficient to enable any one to understand the greater part of the current biological literature, in so far as it relates to vegetable organisms. For the student who desires to pursue the subject further, or who intends to make botany a special study, this book aims to lead him to become himself an observer and investigator, and thus to obtain at first hand his knowledge of the anatomy and physiology of plants : accordingly the presentation of the matter has been made such as to tit the book for constant use in the Laboratory, the text supplying the outline sketch, which may be filled up by each student, with the aid of the scalpel and compound microscope. This book is an expansion and considerable modi- fication of the material of several courses of lectures iv 1'liKFACE. annually delivered to college students. In general plan, Part I. follows pretty nearly that of Sachs' ad- mirable "Lehrbuch," and in many instances it has seemed to me that I could not do better than to adopt the particular treatment which a subject has received at the hands of the distinguished German botanist. This has been rendered possible through the liberality of my publishers, and the courtesy of Engelmann of Leipzig, the publisher of many of Sachs' works, by which many of the cuts of the "Lehrbuch" are here reproduced. This book will thus, to a considerable extent, serve as an introduc- tion to that work. Free use has also been made of the recent works of De Bary, Hof meister, Strasbur- ger, Nageli, Schwendener, and others, to whose writ- ings numerous references are made. In Part II. the general disposition of the lower plants is a considerable modification of that proposed by Sachs ; that of the higher plants is made to con- form to the system of classification in vogue in this country and in England, as outlined in Dr. J. D. Hooker's "Synopsis of the Classes, Sub-classes, Co- horts and Orders," in the English edition of Le Maout and Decaisne's "Traite Generate de Botan- ique," and as given much more fully in Bentham and Hooker's still unfinished "Genera Plantarum." The notes upon the economic values of the more impor- tant plants of each order are based upon my own lec- tures upon Economic Botany. I have also freely used the similar notes in Le Maout and Decaisne's work, cited above ; Balfour's " Class-Book of Bot- any," Archer's "Economic Botany," Smith's "Do- mestic Botany," Laslett's "Timber and Timber Trees," etc., etc. Necessarily, there is but little that is really new in a treatise like this. Aside from a more or less important and original arrangement of the matter, so as to PREFACE. V secure a more logical presentation of the subject, there are but two considerable innovations, consist- ing (I.) in the recognition (in Chapter VI.) of seven quite well marked kinds of tissue. In this, however, while not adopting De Bary's classification, I have followed his method of treating the subject, as given in his recent work on the comparative anatomy of plants (" Vergleichende Anatomic der Vegetations- organe der Phanerogamen und Fame.") (II.) The second considerable innovation occurs in Part II. ; it consists in raising the Protophyta, ZygosporefiB, Oos- poreae and Carposporese to the dignity of Primary Divisions of the vegetable kingdom, co-ordinate with the Bryophyta, Pteridophyta and Phanerogamia. The usefulness of both of these departures from the common practice has been subjected to the test of the laboratory, and the lecture and class-room, with the most satisfactory results ; and I am led to hope that in the hands of others they may also serve to give a clearer and more accurate notion of the struc- ture of plants. Should they do this they will need no further apology or defense. Of the illustrations, many are entirely new ; many others have been re-drawn, from various sources, with slight modifications, expressly for this work, and all from other sources are specially acknowl- edged in their places. I desire here to acknowledge my indebtedness to Dr. Asa Gray, whom it is an honor to own as my sometime teacher, for kindly aid and counsel in the preparation of the lectures upon which this work is based ; and in the same way I am indebted to Dr. G. L. Goodale, Dr. W. G. Farlow and Professor A. N. Prentiss. For aid in the immediate preparation of the material for the press, acknowledgment is due many of my personal friends : Mr. J. C. Arthur fur- nished the original drawings of the water-pores of VI PKKFAVE. Fuchsia, and of various tissues of Echinocystis ; Professor H. L. Smith, of Hobart College, New York, contributed the sketch of the classification of the Diatomaceie ; Dr. T. F. Allen furnished a synop- sis of the classih'cation of the Characese ; Dr. B. D. Halsted also furnished material and notes upon our native species of Characese ; my colleague, Professor W. H. Wynn, kindly determined some of the more difficult etymologies ; to my wife I am deeply in- debted for efficient aid in the laborious tasks of proof-reading and indexing. Should this book serve to interest the student in the study of plants as living things, should it succeed in directing him rather to the plants themselves than to the books which have been written about them, should it contribute somewhat to the general read- er s knowledge of the structure and relationship of the plants around him, the objects kept in view in its preparation will have been attained. C. E. 13. BOTANICAL LABORATOKY, i IOWA AGRICULTURAL COLLEGE,)" AMES, IOWA, April 12, 1880. PKEFACE TO SECOND EDITION. In this edition a few errors which had escaped detection in the first issue have been corrected, and several minor changes in the text have been made, which the lapse of a year and a half since the manuscript left my hands rendered necessary. C. E. B. May 21, 1881. CONTENTS. PART I. GENERAL ANATOMY AND PHYSIOLOGY. CHAPTER I . PROTOPLASM. PAGE General Characters Chemical Composition Consistence Power of Imbibing Water Vacuoles Physical Activity Naked Protoplasm Protoplasm Enclosed in Cell Walls 1 CHAPTER II. THE PLANT-CELL. General Statement Ectoplasm and Endoplasm Bauds and Strings of Protoplasm Nucleus Size of Cells Forms of Cells The Cell the Unit in Plants 15 CHAPTER III. THE CELL-WALL. Composition Growth in Surface Growth in Thickness The Markings on Cell Walls Theories as to the Mode of Thick- ening Stratification of the Cell Wall Formation of Chem- ically Different Layers The Formation of Mucilage Incom- bustible Substances in the Wall 21 CHAPTER IV. THE FORMATION OF NEW CELLS. Cell-Formation by Division : (a) Fission ; (6) Internal Cell-Forma- tion Cell-Formation by Union Examples 36 vni CONTENTS. CHAPTER V. THE PRODUCTS OF THE CELL. PAGE g 1. Chlorophyll 2. Starch, Composition, Form, Molecular Structure Grauulose and Starch-Cellulose Formation of Starch Granules in the Chlorophyll-Bodies Formation of Ordinary Starch Granules 3. Aleurone and Crystalloids 4. Crystals in Cells 5. The Cell Sap 6. Oils, Resins, Gums, Acids and Alkaloids fiu CHAPTER VI. TISSUES. 1. The Various Aggregations of Cells : (a) Single Cells ; (b) Fam- ilies ; (c) Fusions ; (d) Tissues ; The Cell- Wall in Tissues 2. The Principal Tissues Parenchyma Collenchyma Sclerenchyma Fibrous Tissue Laticiferous Tissue Sieve Tissue Tracheary Tissue 3. The Primary Meristem 63 CHAPTER VII. THE TISSUE SYSTEMS. 1. The Differentiation of Tissues into Systems 2. The Epi- dermal System of Tissues Epidermis Trichomes Stomata 3. The Fibro- Vascular System of Tissues General Structure The Fibro- Vascular Bundles of Pteris, Polypodium, Adiautum, Equisetum, Selnginella, Lycopodium, Zea, Acorus, Ricinus and Ranunculus Of Xylem and Phloem Collateral, Concentric, and Radial Bundles Development of Fibro- Vascular Bundles 4. The Fundamental System The Tis- sues it Contains Cork Lenticels 89 CHAPTER VIII. INTEHCKLLULAK SPACES, AND SECRETION RESERVOIRS 128 CHAPTER IX. THE PLANT-BODY. 1. Generalized Forms Thallome Caulome Trichome Root- Particular Relations of Phyllome to Caulome General Modes of Branching of Members 2. Stems The Punctum Vegeta- tionis Buds Adventitious Stems 3. Of Leaves in General 4. The Arrangement of Leaves 5. The Internal Struc- ture of Leaves 6. The Roots of Plants, Structure, Root-Cap, Growth Formation of New Roots Arrangement of Roots. . . 133 COXTKNTS. IX CHAPTER X. THE CHEMICAL CONSTITUENTS OF PLANTS. PAGE 1. The Water in the Plant Amount of Water in Plants Water in the Protoplasm Water in the Cell Walla Water in the Intercellular Spaces Equilibrium of the Water in the Plant Disturbance of Equilibrium Evaporation of Water Amount of Evaporation The Movement of the Water in the Plant 2. As to Solutions 3. Plan*. Food The Most Important Elements The Compounds Used How the Food is Obtained How Transported in the Plant 166 CHAPTER XI. THE CHEMICAL PROCESSES IN THE PLANT. 1. Assimilation 2. Metastasis Its General Nature Trans- formation of Starch Nutrition of Protoplasm The Storing of Reserve Material The Use of Reserve Material The Nutri- tion of Parasites and Saprophytes The Formation of Alkaloids Results of Metastasis 178 CHAPTER XII. THE RELATIONS OF PLANTS TO EXTERNAL AGENTS. 1. Temperature General Relations Absorption of Water as Af- fected by Temperature Evaporation Assimilation Metasta- sis Death from too Hijrh a Temperature Death from too Low a Temperature 2. Light : General Relations of Light to Assimilation, Light, and Metastasis 3. Heliotropism 4. Geotropism 5. Certain Movements of Plants : General Statement, Spontaneous Movements, Movements Dependent upon External Stimuli, Movements of Nutation, Movements of Torsion... ..184 PART II. SPECIAL ANATOMY AND PHYSIOLOGY. CHAPTER XIII. CLASSIFICATION Principles of a Natural Classification Critical A Comparison of several Systems 202 x CONTENTS. CHAPTER XIV. THE PKOTOPIIYTA. PAGE 1. Myxoinycetes 2. Schizoinycetes 3. Cyanophycea* 200 CHAPTER XV. THE ZYGOSPORE^S. g 1. Zoospome g 2. Conjugate 220 CHAPTER XVI. THE OOSPOKE,*:. 1. Volvox and its Allies 2. (Edogoniese 3. Cceloblasteae 4. Fucacese 243 CHAPTER XVII. THE CARPOSPORE.K. 1. Coleochaete 2. Florideae 3. Ascomycetes 4. Basidio- mycetes 5. Characeae 6. The Classification of Thallo- phytes 270 CHAPTER XVIII. THE BRYOPHYTA. 1. Hepatic* 2. Musci 341 CHAPTER XIX. THE PTERIDOPHYTA. p 1. Equisetinse 2. Filicinse 3. Lycopodinse 361 CHAPTER XX. THE PHANEROOAMIA. 1. General Characters 2. Gymnospernue 3. Angriospermae Glossology of Anjfiosperms The Tissues of Angiosperms Classification and Economic Botany of Monocotyledons Class- ification and Economic Botany of Dicotyledons 389 CHAPTER XXI. CONCMTDING OBSERVATIONS. The Number of Species of Plants The Affinities of the Groups of Plants The Distribution of Plants in Time 566 BOTANY. PART I. GENERAL ANATOMY AND PHYSIOLOGY. CHAPTER I. PROTOPLASM. 1. If W e examine a thin slice of any growing part of a plant (Fig. 1) under a microscope of a moderately high power (400 to 500 diameters), there may be seen large num- bers of cavities which are more or less filled with an almost transparent semi-fluid substance. In very young parts, as in buds and the tips of roots, this substance entirely fills the cavities, and makes up almost the whole mass, while in older parts ifc occurs in less quantity, and usually disappears in quite old tissues. This substance is the living portion of the plant, the active, vital thing which gives to it its sensi- bility to heat, cold, and other agents, and the power of mov- ing, of appropriating food, and of increasing its size ; it is, in fact, that which is sensitive, which moves, appropriates food, and increases in size. This sensitive, moving, assimilating, and growing substance is named PROTOPLASM. * It is a fact of great biological interest that in animals the essential constituent of all living parts is a substance similar to the protoplasm of plants. We cannot distinguish the two by any chemical or physical tests, and can only say that, taken as a whole, the protoplasm of plants * So named by its discoverer, Dr. Hugo Von Mohl, in 1846. It is the Bioplasm of Dr. Lionel Beale and his followers. BOTANY. differs from that of animals in its secretions. And yet these secre- tions are not strictly confined to plants ; cellulose, starch, chlorophyll, and other products of vegetable protoplasm formerly regarded as pe- culiar to plants are now known to occur in undoubted animals. Botanists and zoologists have labored long in vain to discover absolute differences between the animal and the vegetable kingdoms; between the higher plants and the liiglier animals there are great and constant differences ; in none of the higher animals, for ex- ample, is chlorophyll produced ; but. in the lower orders of both kingdoms not one of the differences observed to hold between the higher plants and --_ animals exists. 2. The exact chemical compo- sition of protoplasm has not hith- erto been made out, but it is known to be an albuminous, watery substance, combined with a small quantity of ash. It is probably a complex mixture of chemical compounds, and not a single compound. It contains at some time or another all the chem- ical constituents of plants. Oil, granules of starch, and other or- ganic substances are frequently present in it, but they are to be re- garded as products rather than proper constituents of pro! oplasm. Fig. 1. A little more than half of i longitudinal section of the apex of yonng root of the Indian corn. (a) Water makes up a considerable Tlie part above is the body of the part of the bulk of ordinary protoplasm, root, that below it is the root-cap ; , . , . / r, thick outer wall of the epidermis; and is much more abundant in its m young pith-cells; /.young wood- active than in its dormant conditions, cells ; g, a young vessel ; , t, inner T , younper part of root-cap ; a, a, out- In the protoplasm ot fulif/o tariai.s er^oldir part of rootKjap.-After ( one of the S i ime Moulds) just before the formation of its spores there is 70 per cent of water ; in dry seeds, on the other hand, the amount is not more than about 8 to 10 per cent. (b) As to its molecular constitution, Strasburger holds* that proto- plasm is composed of minute solid particles (not, however, of a crystal- line form), separated from each other by layers of water (see Cell-wall * " Studien tiber Protoplasma," 1876. PROTOPLASM. paragraph 37, and Starch, paragraph 69). The thicker the layers of water are, the more watery is the protoplasm, and vice versa. (e) Tests. 1. If a protoplasmic mass is moistened with a solution of iodine, it at once assumes a deep yellow or brown color. 2. If treated with a solution of copper sulphate and afterward-* with potash, it assumes a dark violet color. * f Fig. 2. Parenchyma cells from the central cortical layer of the root of FrUittati^ ii/tpenalis, longitudinal sections. A, very young cells lying closu above the apex of tlie root, still without cell sap or vacuoles. B, cells of the same description about i wo millimetres above the apex of the root ; by the entrance of cell sap the vacuoles , s, s have been Conned. G, cells of the same description about seven to eight mil- limetres above the apex of the root. In all the figures, A, cell-wall ; p, protoplasm ; &, nucleus ; kk, nucleoli ; s, vacuoles ; sey, swelling of the nucleus under the influ- ence of the water in preparing the specimen. X 500. After Sachs. 8. Treated with a solution of sugar, and afterwards with sulphuric acid, it becomes rose-red. 4. The presence of protoplasm may be demonstrated in a tissue by the application of various staining fluids, as magenta, carmine, etc. BOTANY. 5. In a dilute solution of potash protoplasm is dissolved ; if, how ever, the solution is concentrated, tlie form of the protoplasm remains unaltered for weeks, but upon the addition of water it at once dissolves. 6. Protoplasm coagulates upon the application of heat (50 degrees Centigrade), or when immersed in alcohol or dilute mineral acids. 3. In consistence protoplasm is a soft-solid substance, varying from an almost perfect fluidity on the one hand to a considerable degree of hardness and even brittleness on the other. This difference in con- sistence is mainly due to the vary- ing amounts of water imbibed by it, hence the same mass may at different times vary greatly in this regard. Generally there may be seen in protoplasm a large number of minute granules enclosed in a transparent medium (Fig. 2, A) ; in some instances, however, the grannies are entirely wanting, or nearly so. By the withdrawal of these granules for a little distance from the surface toward the cen- tre, a mass of granular protoplasm w,. 3.-o P ticai ^cTion of a re- < the endoplasm) may appear to be trading branch of a large piasmo- surrounded by a hyaline envelope, diumof Fuligo variants (.Ethalium , i . fepticum of authors); the narrow the protoplasmic SK111, 01' CCtO- inner granular mass of protoplasm , /.i Tr . 7 7 / T is seen to be surroimdod by a broad plasm (the Hdlttschicllt of PnngS- hyaline portion, the ectoplasm, i j rr j i t cu. which in this case is radially streak- heim, and HaUptpldSmCl Of btras- fiu burger) (Fig. 3). It is almost al- d by a hyalineen- wavs formed when protoplasm is veiope. X aoo.-Aftcr Hofmeister. exposed in water or air ; but it, or something very much like it, appears to be generally present, even in closed cells. (a) The fine granules are probably not proper constituents of proto- plasm, but finely divided assimilated food-materials immersed in the proper protoplasm, which is itself colorless and transparent. Proto- plasm destitute of granules may be found in the cotyledons of the bean (PJiaseolus), In other cases, e.g., in the zygospores of Spirogyra, the granular and coloring matters are so abundant that the hyaline basis can no longer be distinguished. PROTOPLASM. 5 (6) fctrasburger* maintains that tlie hyaline envelope is not simply a portion of the basis or ground substance of the protoplasm deprived of its granules, but that it is a definite modification of it, and endowed with various properties quite distinct from those of the ground sub- stance. 4. Active protoplasm possesses the power of imbibing water into its substance, and as a consequence, of increasing its mass. This power varies with the changes in external, and also in internal conditions ; many seeds, for example, which do not swell up (through absorbing water) in cold water, will do so when placed in that of a higher tempera- ture ; but in some seeds it appears that imbibation of water will not take place until after a period of rest. 5. When the amount of water imbibed is so great that the protoplasm may be said to be more than saturated with it, the excess is separated within the protoplasmic mass in the form of rounded drops, termed Vacuoles (Vacuoli). In closed cells these may become so large and abundant as to be separated only by thin plates of the protoplasm (Fig. 2, B). As such vacuoles become still larger, the plates are broken through, and eventually we may have but one large vacuole surrounded by a thin layer of protoplasm, which lines the interior of the cell wall (Fig 2, C). In this way some masses of protoplasm assume a bladder-like or vesicular form, so unlike their original form that until -very recently their real nature has not been understood.! Frequently when the plates which separate vacuoles break down, instead of breaking entirely away they become pierced with several Urge openings, leaving strings or bauds of protoplasm which extend across the cavity. Occasionally, when vacuoles unite, small masses of the protoplasm which previously separated them become detached as free rounded * " Studien iiber Protoplasma," 1876. See also Qr. Jour. Mic. Science, 1877, p. 124 et seq. f Von Mohl gave to this layer the name Primordial Utricle, and it is still frequently used, but the term is objectionable, and Sachs' name of Protoplasmic Sac is to be preferred. Treatment with glycerine, strong alcohol, or any other substance which removes the water, will cause the protoplasmic sac to contract and become visible. BOTANY. masses iu the large vacuole ; these again may produce vacuoles within themselves, and thus give rise to a peculiar and at first sight perplex- ing structure (Fig. 4). 6. The most remarkable peculiarity of living protoplasm is its physical artirity. When the proper conditions are pres- a living mass of protoplasm is apparently never at rest, but, on the contrary, continually altering its shape and changing the position of its constit- uent parts. The move- ments are all of the general nature ; same each one may be regard- ed as the aggregate re- sult of the chemical and physical changes taking place in the substance of the protoplasm. We may study the ac- tivity of protoplasm under two conditions, which will give us the two cases. (1.) The Activity of Naked Pro- Fig. 4.-Forms of the protoplasm contained in toplasm, and (2. ) The cells. A and B, of Indian Com (Zen mai*) ; A, A , . , * T> \ i cells from the first ieal-sh.-ath of a germinatinsr Activity of Protoplasm plant, showing the frothy condition of the proto- endoged j n fl Ce ll- W all. plasm, the many vacuoles plates. B, cells from the first intcrnodf of the rated by thin 7. The Activity of masses, in'each of which there Naked Protoplasm. is a vacuole, b ; these are the so-called " sap-vesi- cles." 6', a cell from the tuber of the Jerusalem lllC lOW Organisms Artichoke (.lli-limitlm* /"i?w>/*> after the action of , ,. iodine and dilute sulphuric acid; h, cell-wall; *, kllOWll as the nucleuB^.contracteaprotopla.m.-After Sachs. germinating pi mt ; the protoplasm is broken up into many rounded i present the best examples of the activity of naked vegetable protoplasm. In their plasmodia (as the masses of naked proto- plasm are called), many kinds of movements may be observed, the commonest of which is streaming. In plasmodia com- posed of thin (i.e., watery) protoplasm, streams or currents of the latter may be seen running in various directions PROTOPLASM MOVEMENTS. 7 (Fig. 5). The streams are made clearly visible by the motion of the granules which are carried along by the moving hya- line portion of the protoplasm. After running in one Fig. 5. A email mass of the naked protoplasm (plasmodium) of Dldymium er K/a ; the arrows show the direction of the currents, x 30. After Hofmeister. direction for some minutes (about five) the current stops, and then it usually sets in an exactly opposite direction for about the same length of time, and carries back the previ- ously moved protoplasm. The formation of the new current may be explained as follows ; Let A ............ B be a stream in which the movement is from A to B ; clearly there will be an aggregation of protoplasm about B. When the current in the direction A B stops, the new one, in the reverse direction, B A, begins at A, by the movement toward it of the particles nearest to it ; next the particles further off move toward A ; after this, those still further off, and so on. The current extends back- ward. So, too, when a stream begins de novo, it is propagated back- ward from the point of beginning. 8. Mass-Movement (Amoeba-Movement). In the flowing back and forth in the streams the movement may be greater in one direction than in the other ; this causes a slow motion of the whole plasm odium in the direction of the greatest movement. When this takes place in the case of streams which begin in the mar- gin of the plasmodium, protuberances of vari- ous shapes arise ; these may be extended into branches (pseudopo- dia), which may again be branched one or times - By the r\t flipon a Complex moving and changing network is formed. (See Fig. 140, page 208) There is pos- sibly to be separated from the above-described mass-move- ment that more or less rapid change of external contour which has, from its resemblance to the motions of the Amoeba, been denominated the Amoeba-movement (Fig. 6). It is best observed in the so-culled "Amoeba-form " stage of *he swarm-spores of the Mvxomycetes. 'g m # Fig.6.-0ntlineof a plasmodium of ZHdymiwm more nerpula forming pseudopodia. The heavy black line indicates he outline at the beginnin of the observation ; the psendopodium a-b formed in 8 branches *. c-d in 30, and c-e in 55 seconds, After Hofmcister. PROTOPLASM MOVEMENTS. 9 While in thinner protoplasm the streaming and mass- movements are always horizontal, or, at least, parallel witli the surface upon which the plasmodium rests, in the case of tougher protoplasm they may give rise to branches which have an upward direction, as in the formation of sporangia. 9. Effect of External Influences. The movements of the protoplasm of the Myxomycetes, and probably to a greater or less extent of all plants, are suspended by certain external influences. Violent jarring, pressure, a thrust as with the point of a pin or pencil, electrical discharges, sudden changes of the temperature, and sudden changes in the concentration of the surrounding fluid, stop the move- ments, and cause the plasmodium to contract into one or more spheroidal masses. When these influences cease, if they have not been so violent as to destroy the organization of the protoplasm, it returns after a greater or less length of time to its original form, and the movements are resumed. (a) The effect of mechanical disturbances (jarring, pressure, and thrust) may be best studied in the tougher or least fluid plasmodia (e.g. , of Stemonitis fusca). (b) The effect of electrical discharges may be studied by placing a small plasmodium (e.g., Didymium serpula) upon a glass plate provided with platinum points which are in connection with the poles of an induction apparatus. When a discharge takes place through a narrow branch (pseudopodium) it contracts so violently as to be broken up into a row of little spheres ; if it takes place through the mass of the plas- modium it becomes more or less spherical by its contraction. ,In any case, if the shock has not been too severe, the protoplasm after a while returns to its normal shape again.* (c) The plasmodium of Didymium serpula, when removed from a tem- * Kuhne performed the following curious experiment. Taking a portion of the plasmodium of Didymium serpuln., in its resting state, he mixed it with water so as to make a pulpy or pasty mass. With this he filled a piece of the intestine of a water-beetle, and tying the ends, laid it across the electrodes of an induction apparatus. The pre- paration was kept in a film of water in a damp chamber for twenty-four hours, at the end of which time it was considerably distended. He now allowed the electrical current to pass through it, when it contracted itself "like a colossal muscle-fibre." Upon extending it by pulling at the ends, and then sending through it a stronger electrical current, it toiitractt'd itself v.ue third of its length. 10 BOTANY. perature of 20 C. to one of 30 C. (68 to 86 Fahr.) ; withdraws its pseud- opodia and ceases its activity iu the space of five minutes. In au hour alter the restoration of the normal temperature (20 C.) the movements begin again. If the temperature is raised to 35 C. (95 Fahr.) the organization of the plasmodiuni is destroyed. The plasmodium of Ftdigo variaiis, Sommf. (^tltalinm septicum, Fr.), when placed in a chamber surrounded by ice, contracts into a rounded form and ceases all motion ; upon gradually raising the tem- perature again the normal state is resumed. (d) In glycerine, a concentrated solution of sugar, a five per cent solu- tion of potassium nitrate, or a five per cent solution of sodium chloride, a plasmodium contracts, and becomes rounded and motionless. A suddi-u decrease in the concentration of the solution by which a plasmodiuni is surrounded also results in a stoppage of its movements. A plasmo- dium of Didymium serpula, when placed in a one per cent solution of potassium nitrate, and allowed time to regain its activity, suddenly rounds itself up and stops its movements when the preparation is washed out with distilled water ; after the lapse of a few minutes (ten to twelve) the activity begins to show itself again, and in half an hour the normal state is restored. 10. Ciliary Movement. The swimming of swarm-spores, spermatozoids, and many other naked protoplasmic bodies, is due to the rapid vibratory motion of extremely small whip- like extensions of the hyaline portion of the protoplasm. Examples of ciliary movement are very common. In some swarm- spores, as in those of Vaucheria, the whole surface is covered with short cilia ; in others, as in (Edogonium, the cilia form a crown al.out the hya- line anterior extremity ; those of Pandorina and Cladophora, and the spermatozoids of Bryophytes and Pteridophytes, have two or more cilia ; while the swarm-spores of Myx<>mycetes have but one. The rapidity of tli e swimming motion produced by cilia is consider- able, as shown by measurements made by Hoi'meister* in the case of swarm-spores, viz. : Fttliyo varians (^ffithalium septicum). .. .7 to .9 mm. per second. Lycogola epidetidrum .33mm. " (Edogonium tesicatum 15 to .20 mm. " " Vancheria sp 10 to .14 mm. " " 1 1 .The Activity of Protoplasm Enclosed in a Cell- wall. The movements of protoplasm in closed cells differ but little from those in naked ones ; the differences are sucli as are due to the fact that in the latter case the protoplasm is * " Lehre von der Pflanzenzelle," p. 30. PROTOPLASM MOVEMENTS. 11 free to move in any direction, while in the former its move- ments are greatly restricted by the surrounding walls. In closed cells there are two general kinds of movements one a streaming, the other a mass movement comparable to the streaming and Amoeba movements of the naked cells or pro- toplasmic masses. No movement takes place, however (at any rate to no great extent), until the vacuoles are quite large. 12 The streaming movements occur in the protoplasmic strings, bands, and plates which cross or separate the vacu- oles, and in the lining layer of protoplasm which invests the inner surface of the cell-wall. The motion, in many cases, shows the same alternation as in the Myxomycetes, the direc- tion of the streaming usually being reversed after the lapse of a few minutes. The mass-movement in closed cells is not as clearly sepa- rated from the streaming as in naked cells. It usually con- sists in a sliding or gliding of the protoplasm upon the inner surface of the cell-wall, in much the same way as the naked plasmodium of one of the Myxomycetes moves upon the sur- face of its support. The limited space in which its move- ment must take place in closed cells, and its disposition over the whole inner surface of the wall, compel the protoplasm to move in opposite directions upon opposite sides of the cell. There is thus a kind of rotation of the protoplasm when the movement of all its parts is uniform. (a) The streaming movements may be studied in the stamen-hairs of Tradescantia Virginica, the stinging hairs of the nettle (Urtica), the hairs of Cucurbita, Ecbalium, and Solatium tuberosum, the styles of Campanula, the easily separated cells of the ripe fruit of Symphoricar- pus racemosus, the young pollen grains of (Enothera, and the paren- chyma of succulent monocotyledons e.g., in the flower peduncles and the filaments of Tradescantia. The parenchyma cells of the leaves of many trees and of the prothallia of ferns and Equisetums show a net- work of hyaline strings in which a streaming may with difficulty be seen. Among the lower plants good examples may be found in the hyphae of some Saprolegniae, and in the cells of Spirogyra, Closlerium, Denti- cetta, and Coscinodiscus. (b) In many capes (e.g., in the unfertilized embryo sac of many Phanerogams, in the young endosperm cells, and in the spore-mother- cells of Anthoceroslwvis) where the strings and bands resemble those in the cases cited above no movement of the protoplasm is visible, 12 BOTANY. doubtless because of the mechanical injury of the cells in making the preparation, and the disturbing influence of the water in which it is mounted. (c) lu the stamen-hairs of Tradeseanlia Virgin-tea the protoplasm Fig. 7. An optical section of a cell of one of the stamen-hairs of Tradefcantia finjMtUe, after treatment with a solution of sugar. The protoplasmic sac has partly collapsed, on account of the withdrawal of some of the interior water by the sugar solution. At the bottom of the cell is the lame nucleus ; in the strings and bands of protoplasm there are streamings of the protoplasm, shown by the arrows. After Hofmeister. forms a rather thick layer over the inner surface of the cell-wall, and in some part of this layer the nucleus lies imbedded. From the nucleus and from various parts of the protoplasmic layer there pass to the opposite side of the cell thicker or thinner bands and strings, always PROTOPLASM MOVEMENTS. 13 however, more or less parallel with the longer axis of the cell (Fig. 7). In a string there may toe one, two, or three currents ; when there are two they are in opposite directions ; when there are three the central one takes one direction and the two outer ones the other. The strings are not stationary in the cell, but, on the contrary, they change their position with a considerable rapidity, and in a prepara- tion soon pass out of the focus of the microscope.* By this change of place two strings may come together and fuse into one, or a string may pass to the side of the cell and become obliterated by fusing with the protoplasmic sac. New strings may be formed by a process exactly opposite to the one just described. A stream in the substance of the lining protoplasm forms a ridge projecting into the vacuole ; this ridge gradually becomes higher, and finally breaks away from the protoplas- mic sac, retaining its connection only at the ends. After a stream has been running in a certain direction for from ten to fifteen minutes, the motion suddenly becomes slower and soon stops entirely for from a few seconds to several minutes, and then begins to move in the opposite direction. The new movement begins and spreads as in the Myxomy- cetes (see paragraph 7). (d) In the hairs of Cucurbita Pepo the arrangement of the protoplasm is much as in Tradescantia. The strings and bands are, however, broader, and frequently contain several currents, and the nucleus, instead of being imbedded in the lining layer of protoplasm, is in a centrajly placed mass. There is a more rapid change in the form and position of the bands and strings than in Tradescantia, but the streaming motion is, on the contrary, considerably slower. The reversal of the streaming currents takes place in from seven to twenty minutes. (e) In most cases the streams lie in the lining protoplasmic layer of the cell, or form low ridges upon its inner surface. This is the case in the hairs of the style of Campanula, in hyphse (of fungi), and in the suspensor and young embryo of Funkia cterulea. In long cells, the movement being parallel with the longer axis, there may be, as in the pollen tube of Zostera marina, currents passing up one side and down the other.f * This fact must be borne in mind in studying the movements of pro- toplasm in these cells, otherwise grave mistakes may be made. Ono string may move out of focus, and another, with a contrary current, may move into it, and thus a reversal of the current in the first string may erroneously be supposed to have taken place. f To study the movements of protoplasm in pollen tubes it is usual y necessary only to make a thin longitudinal slice of the stigimt, and to mount and cover it in the usual way, using no water, however. After placing it under the microscope the preparation should be carefully crushed, when some of the pollen tubes may be distinctly seen. Their movements frequently continue for some hours in such prepnrations 14 nor ANY. (/) The passage from the condition in the last examples (the so- called circulation of protoplasm) is an easy one to the cases where the whole mass of protoplasm moves along the cell-wall as a broad stream, passing up one side and down the other (the so-called rotation of pro- toplasm). Common and well-known examples of this kind of mass-move- ment occur in Cham, Naias, and Vallisneria. It may also (on the authority of Meyen) be studied in the root-hairs of many land plants e.g., of Impatiens Balmmiiia, Vitia falm, Ipoma'a purpuren, < ucumis, Cucurbita, Ranunculus sceleratus, and Marchantia polymorpha. CHAPTER II. THE PLANT-CELL. 13. In some cases plant protoplasm has no definite or constant form. This is its permanent condition in some of the lowest plants e.g., the Myxomycetes. In most other lower plants, and in all the higher ones, it has this condition only temporarily, if at all. In the great majority of cases, however, the protoplasm of which a plant is composed has a definite, and, within certain limits, a constant form. It usu- ally appears in more or less rounded or cubical masses of minute size, and which may or may not be surrounded by a cell-wall. In this condition it constitutes the Plant-Cell. The undifferentiated protoplasm of the Myxomycetos reminds us of the lower Monera among animals. In Bathybius and Protamoaba the naked protoplasm of which they are composed has no constant form. In Protoinyxa we have a few simple transformations which are in every respect comparable to those of the Myxomycetes.* In higher animals the protoplasm exists in minute and definitely marked masses, termed cells, or corpuscles, and these have been shown to be the exact horno- lojjues of the cells of plants. 14. While in young cells provided with a wall the pro- toplasm fills the whole cavity, as in A, >ig. 2 (p. 3), in older ones it never does so, and generally these contain only a very small portion of it, as a thin layer covering the inner surface of the cell-wall (B and C, Fig. 2). Close examina- tion shows that this protoplasmic sac consists of (1) a firmer hyaline layer, the ectoplasm, which is in contact with the * See further on this subject in paragraph 222, Chapter XI. For a short account of these interesting animal forms mentioned above, the student, is referred to Dr. Packard's " Zoology for Students and Gen- eral Readers," (p. 18 et seq.) in the series of which the present work forms a part, and his " Life-Histories of Animals," where are also given numerous references to fuller accounts. 16 BOTANY. ^cell-Avail ; and (2) within this a less dense granular one, the endoplasm ; the two layers are, however, not separated from each other by any sharp line of demarkation.* When the endoplasm attains a considerable thickness it Incomes dif- ferentiated into an external denser layer and an internal less dense one. Often one of these layers may be found to be in motion while the other is at rest.f 15. There may almost always be seen in plant-cells bands '.or strings of protoplasm which lie in or between the vacu- .oles (Fig. 2, B). They are at first thickish plates which separate vacuoles, but afterward they become narrower as the vacuoles enlarge, and at last they disappear entirely. In these bands and strings, as previously stated (paragraph 12), streaming movements are frequently to be seen. 16. Each of the protoplasm masses constituting the cells of most plants usually has a portion of its interior substance differentiated into a firmer rounded body, the nucleus Its normal position is in the centre of the cell ; but it may be displaced and pushed aside by the vacuoles, so that in an optical section of the cell it may often appear to be in the margin. The nucleus is to be regarded simply as a modified part of the protoplasm of the cell, and not as something dis- tinct from it. It may dissolve, and its substance pass into that of the remainder of the cell ; afterward a nucleus may form again ; and this may occur a number of times. Com- monly in each nucleus one or more small rounded granules may be seen ; these are called the nudeolL The nucleus . may form a skin (hautschicht) about itself, and vacuoli may be present in its interior. 17. Cells are of very varying sizes. They differ in dif- ferent plants, and also in the different parts of the same plant. In but few cases, however, are they of great size, by far the larger number being microscopic. The most striking * These two layers were first described by Pringsheim in his " Theorio der Pflanzenzelle," 1854. f Cf. Strasburger, " Studien uber Protoplasms," 1876 ; and Qr. Jr. Me. Science, 1877, pp. 124-132. THE PLANT-CELL. examples of large cells are found in the Thallophytes ; Nitella, for example, has cells 50 mm. (2 inches) long, and 1 mm. (.04 inch) thick. According to Von Mohl, the bast-cells of a species of palm (Astrocaryum) are from 3.6 to 5.6 mm. (.13 to .21 inch) in length. For ordinary plants the average size of the cells may be given as from .1 to .02 mm. (.004 to .0008 inch). From this average size the dimensions of cells decrease to exceedingly small magnitudes. In the Yeast Plant (Saccharomyces cerevisice) the cells are about .008 mm. (.0003 inch) in diameter. The cells of Bacterium termo are from .0021 to .0028 mm. long and from .0028 to .0005 mm. broad (.0001-. 00008 by .00008-. 00002 inch). The following table, taken from Hofmeister's " Lelire von der Pflan- zenzelle," is useful as showing how the dimensions of similar cells vary in different plants : TABLE OF DIMENSIONS OF VARIOUS KINDS OF CELLS OF WOODY PLANTS. (In decimals of a millimetre.) ! L, M g jj si gs >i t> 3 2S g ^ S-" 2 . i** 3 I|| *L o gt. P fe^ L) S*w II! s*- jli 5 2.i; I 65 III Cambium-cells, average length Vessel-like wood-cells, average length .201 .308 .413 .528 .339 1.179 .786 1.511 2.020 Bast-like wood-cells, average length .301 .533 .712 1.819 Vescel -cells of the wood, average length Latticed cells of young secondary bark, aver- .205 212 .404 520 .615 BaJt-cells of young secondary bark, average 798 1 W> 403 1 152 2.183 Cells'of medullary ray in the cambium ring, maximum length in tangential section Do. do , maximum width in tangential sec- .321 .437 .178 .838 .466 .049 tion .041 .076 .011 .017 .056 .014 Cells of medullary ray in the young wood, average length in tangential section Do., do., average width in tangential section. .376 043 .519 .077 .285 .019 .567 .037 .630 .075 .095 .019 Cells of medullary ray in the young secon- dary bark, average length in tangential section .342 .912 .468 504 744 m Do., do., average width in tangential sec- tion .057 .066 .031 .076 .075 .026 18 BOTANY. 18. Every free mass of protoplasm tends to assume a spherical form. The free cells of the unicellular water plants are generally more or less rounded, as are also the floating spores of most aquatic Thallophytes. In plants composed of masses of cells their mutual pressure gives them an angular outline. AVhere the pressure is slight the cells depart but little from the spherical shape, but as it becomes greater they assume more and more the form of bodies bounded by planes. If the diameters of the individual cells are equal and the development of the mass of cells has been uniform in every direction, we may have regular cubes, or twelve-sided bodies, i.e., dodecahedra. It is rarely the case, however, that the cells have a perfectly regular form. Even when their diameters are approximately equal, they are generally so much distorted that they are best described as irregular polyhedra. 19. It much more frequently happens that cells grow more in some directions than in others, and thus give rise to elongated and many irregular forms. In many of the Thallophytes the long filaments composing the plants are made up of elongated cylindrical cells placed end to end ; while in others the cells are repeatedly and irregularly branched. In higher plants many elongated cells occur, but here, by pressure, they generally become prismatic in cross-section. (a) Many forms of cells Lave been enumerated, but they may all be arranged under the two principal kinds indicated above, viz., the short, and the elongated. As will be more fully shown hereafter, the various kinds of short cells constitute what is called Parenchyma; hence the cells themselves are termed Parenchymatous cells, or Paren- chyma cells. Similurly, certain kinds of the elongated cells constitute Prosenchyma, and hence such are termed Prosenchyniatous cell?, or Pn senchyma cells. While it is impossible to draw an exact line be- tween parenchymatous and prosenchymatous forms, yet the terms are valuable, and are in constant use to indicate the general form. (b) Duchartre* has made an excellent classification of the prin- * In his Elements de Botanique," second edition, a large and valuable work, which the student may profitably consult. THE PLANT-CELL. cipal forms of cells, which is given below in a slightly modified form: Cell globular or ovoid, in section round or oval .... Spheroidal. Cell polyhedral. Polyhedral. Cell a parallelo- pipedon, in section rectangular CubmdcU. Cell tabular, with an elongated rectangular s e c - tion Tabular. Cell short (Parenchyma-- tow). Outline smooth, or without promi- With prominences. f Cell ramose, having short and irregular projec- tions Ramose. Cell star-shap- ed, having long projections which are more regular. . Stellate. Cell elongated. Cell cylindrical, with its ends at right angles to its axis, or but little inclined Cylindrical. Cell prismatic, with its ends at right angles to its axis, or but little inclined Prismatic. Cell fusiform [cylindrical or pris- matic], with its ends oblique and pointed Fusiform (Prosenchymcir- tous). 20. When one or more sides of a cell are not in contact with other cells, as is the case with those cells which com- pose the surface of plants, the free sides are generally con- vex, and they often become more or less prolonged, sometimes in a curious way. The velvety appearance of the petals of many plants is due to such prolongations of the free sides of the surface cells (Fig. 8). Of a somewhat similar nature are the tubular extensions of the surface cells of young roots the root-hairs. And here we may also place the curious star- shaped cells which project into the intercellular spaces in the interior of the stem of the water lily (Fig. 9), and those which compose the pith of certain rushes (Fig. 9i). 21. In the 'unicellular plants each cell is an independent BOTANY. organism ; it absorbs nourishment, assimilates, grows, and reproduces its kind. In the higher plants, although this independence is not so evident, it still exists in a considerable degree. Here each cell is an individual in a commu- nity ; but it still has a life-history of its own, a formation (genesis), growth, ma- turity, and death. It is the unit in the plant. Upon its changes in size, form, and structure depend the volume, shape, etai and structural characters of the plant thefree"(upper) sides of the logical Unit of the plant. cells. Mag. After Du- A , , , , . , ehartre. 22. As the whole structure of the plant is an aggregation of cells, so the functions of the whole, or of any part of a plant are but the sum or result- Pie. 9. Fit;. 0. A cross-section through the petiole of Nuphar advena ; s, , star-shaped cells projecting into the intercellular spaces i, i ; g. a reduced fibro-vascular bundle. Magnified. After Sachs. Fig. 96. Stellate cells from the pith of Jiincun e/uKus, magnified. After Du- chartre. ant of the physiological activities of its individual cells. The cell is thus also the Physiological Unit of the plant. CHAPTER III. THE CELL-WALL. 23. In all but the lowest plants the protoplasm of every cell surrounds itself sooner or later with a covering or wall of cellulose. The substance of the cell-wall is a secretion from the protoplasm. Cellulose, as such, does not exist in the protoplasm ; it is formed on the surface when the wall is made. On its first appearance the Avail is an extremely thin membrane, but by subsequent additions it may acquire vary- ing degrees of thickness. The cell-wall forms a complete covering for the protoplasm ; there are at first no openings in it, at. least none that are visible ; later in the life of the cell pores are formed in the wall in some cases, while quite frequently in dead cell-walls there are large perforations of various sizes and shapes. (a) Cellulose is related chemically to starch and sugar. Its composi- tion is C 12 H 20 OIQ. It is tough and elastic. It is but slightly soluble in dilute acids and alkalies, and not at all in water and alcohol. In water, however, it swells up from imbibing some of the liquid, but it shrinks again in bulk when dried. (6) Tests. 1. If cellulose is treated with dilute sulphuric acid, and shortly afterward with a weak solution of iodine, it is colored blue. 2. Treated with Schult/'s Solution it assumes a blue color. (c) In the Myxomycetes, if the large mass of protoplasm composing a plant is somewhat dried, it separates itself into smaller masses, which surround themselves with a cell-wall. Upon applying sulphuric acid and iodine, the characteristic blue color of cellulose appears, showing that the wall is a true wall of cellulose. If, however, any such dried mass of protoplasm is subjected to the proper conditions of moisture and temperature, the cell-wall is dissolved and absorbed into the proto- plasmic mass. Tests applied now utterly fail to show the presence of cellulose. These observations prove the truth of the statement that cellulose is a secretion, and that it is not contained, m of Pteris aquilina, isolated by Schulze's maceration The wall consists of an inner very dense layer, and a central less dense one enclosed betwren two denser ones; these layers are penetrated by pit channels, which are ("en in the further wall in transverse section. B, a similar cell, more thickened. The pits are here long cana's, which are more or less branched. X about 550. Aft. r Sachs. Fig. 14. Brown-walled cells in the stem of Pteris (iquilina. A,& half cell iso- lated and rendered colorless by Schulze's maceration. li, a piece moie strongly magnified (x 550). The fissure-like pits are crossed, i.e.. the fissure is twisted as th thickening increases ; p. a side view of a fissure appearing as a simple channel, since it shows the narrow diameter. C, cross-section; a, boundary lamella; b, c, inner lamtllse. After Sachs. cepting in small isolated spots. As the wall thickens around these spots, they become at first pits, and finally channels. 29. In some cases the pits or channels are simple. straight, or slightly bent extensions of the central cull-cav- ity ; in others they may be branched, as shown in Fig 13#; in cross-section they may be round, as in Fig. 13 A, or elon- THICKENINGS OF THE WALL. gated fissures, as in Fig. 14, or of any form intermediate between these. Pits with elongated fissures may be twisted, giving them, when seen in front view, the appearance of two fissures crossing one another (Fig. 14^4, B). 3O. In the thickening of the cells of the wood of the Coniferae bordered pits arc formed (Fig. 15). Here large round areas of the wall remain thin, and the thickening mass arches over them on all sides in such a way as to form low domes (Fig. 16, F] ; at the top of each dome a small round opening is left, and this permits free communication between the cavity of the cell and the pits formed by the dome. This pro- cess takes place in exactly the same way upon both sides of the common wall of contiguous cells (Fig. 16, B, t, t, and (7). When the partition separating opposite pits breaks away, as it generally does quite soon, the resulting cav- ity is doubly convex in shape (Fig. 16, E). When a pit of this structure is seen in front view, it has the appearance of two concentric circles (Fig. 15, t", and Fig. 16, D) ; the outer one Fig 15.Pinus sylvestris ; longi- tudinal radial section through the wood of H rapidly g owii'g branch ; . , * being formed by the bottom Of (\ (",('", bordered pits, increasing In ,, ., T ,/ . , ,, ase ; st, large pits where c llsof the the pit, and the inner by the medullary rays lie next to the wood- opening at its top. The bordered pits of pines, firs, and other Coniferae may be readily examined by making a longitudinal radial section. They are not found in abundance on the tangential surfaces of the cells. The reel structure of the bordered pits of the Coniferae was not under- stood until quite recently.* Von Mohl, apparently not noticing the * Schacht, in 1859 (Botanische Zcit>mg, pp. 238, 239), and in a memoir in 1860 ("De Maculis in Plantarum Vasis Cellulisque Lignosis"), gave the first correct explanation of the structure of bordered pits. BOTANY. thin partition, thought that the lenticular cavity was formed by the separation of the walls of the two contiguous cells at that place, and cou- A _ ., ^ sequently that they were intercellular. This in- terpretation is still given in some books.* 81. While the bordered pits of the Coniferae are never crowded together, in the cells of some plants they are so numerous as to lie closely side by side (Fig. 17). In such case the first thick- ening of the wall pre- sents itself as a net- work of ridges en- closing elliptical thin places. As the thick- ening advances the ridges increase in height, but at first not in breadth ; later they increase in breadth at the top and overarch the thin areas, much as in the bordered pits of the ru' */., T V.,'o t-omierae. In thlS _ ,__ 'Umirmroy f !-./-> CaSC > hOWCVer, the nr , mi i no - of flin frm nF Opening at t top O f] lfl ^if jo ., n plnnP'at- rl g(J gjjt instead of a . Circle (Fig. 17. A, i x \ mi JT and C, c). The thin Fig. 16. Bordered pits of Knus sylvettris. A, transverse section of mature wood ; ;n, central layer of ihe common wall; t, a mature pit cut through the middle ; t\ the same, but in a thicker part of the sec- tion, the part of the cavity of tne pit seen in perspec- tive ; t", a pit cut through below its openings; B, transverse section through the cambium ; c, cambium ; fi, very young wood-cells ; t, (, very young bordered pits, seen in section ; C, diagram of sectional imd lat- eral views of a young bordered pit ; D, diagram of sectional and lateral views of a mature bordered pit ; E, section of a mature, pit, seen in perspective ; F, section of a younger pit seen in perspective. A and B x 800. -After Sachs. plate separating opposite bordered pita of this kind breaks * See Le Mnout and DecaisneV Traite Generate de Botanique," 1868 [English edition, 1872] ; UHffitli and Hentrey's " Micrographic Die. THICKENINGS OF THE WALL. away as in the previous case, and so free communication between adjacent cells or vessels is established. B FIG. 18. Fig. ir. Bordered pits of the thick root of Dahlia variaUlls. A, front view of a piece of the wall of a vessel, seen from without ; B, transverse section of the same (horizontal, and at right angles to the paper) ; C, longitudinal section of A (vertical, and at right angles to the paper) ; q, septum ; a, the original thin thickening-ridge ; 6, the expanded part of the thickening masses, formed later and overarching the pit ; , thu fissure through which the cavity of the pit communicates with the cell cavity ; at and ,3 the corresponding front view is appended, in order to make the trans- verse and longitudinal sections more clear, x 800. After Sachs. Fig. 18. Scalariform thickening of the walls of a vessel from the underground stem of Pteris aquilina. A, half-vessel, i soli ted by Schulze's maceration ; to D, pieces obtained from stemn hardened in absolute alcohol ; S, a partly diagrammatic view of a vertical section of the wall, seen from within ; c, c, plan of section ; rf, opening to pit ; C, front view of young wall of a vessel ; , unthickened portion of wall; v, thickening-ridge; Z>, vertical section of C; ^section of wall in a place where a vessel adjoins a succulent cell p; the thickening-ridges (g) are only on one side. X 800. After Sachs. tionary," third edition, 1874; Carpenter's "The Microscope," fifth edi tion, t874. BOTANY. 32. The passage from the mode of thickening just de- scribed to the scalariform manner (Fig. 18) is an easy one. Here each longitudinal angle of the cell or vessel is thickened, and from these thickened angles ridges run right and left, from one to the other (Fig. 18, C, v). The after growth of the ridges is essentially the same as in the case of crowded pits ; in fact, the pits here are simply greatly elongated and crowded bordered pits. Eventually the narrow plates be- tween the thickened ridges disappear, as in the other cases. Examples of scalariform thickening are common, especially in the ferns. 33. The development of rings (Fig. 19, v) is nearly like that of the scalariform thickening. Instead, however, of Fig. 19. Longitudinal section of a portion of the stem of Impatiens Baltamiiui. v, annular vessel, v', a vessel with thickenings which are partly spiral and partly an- nular ; v", v'", v"", several varieties of spiral vessels ; v'"", a reiiculated vessel- After Dnchartre. the ridges being short, they extend entirely around the inner surface of the wall. The transition from rings to spirals is a simple one, the thickening taking place in a spiral line, instead of in one passing directly around the wall (Fig. 19, v", v'"). Transitional forms are frequently found (Fig. 19, v'), and many modifications and irregularities occur e.g., in the figure at v'"" is the form known as the reticulated. 34. In all the foregoing cases the marking of the wall has been general ; there are some cases, however, where it is localized. A good example of this is in the formation of the pits of sieve-cells (Fig. 20). The horizontal walls, and also areas upon the longitudinal ones, become thickened reticulately, leaving rather large thin areas, as shown in Fig. 20, q, q. After a while the thin areas become absorbed, THICKENINGS OF THE WALL. 29 allowing the protoplasm of contiguous cells to become struc- turally united. The sieve- like appearance of these modified portions of the wall give to the Cells their name of sieve-cells. 35. The collen- chyma cells which are frequently found beneath the epider- mis of the succulent parts of h i g h e r plants afford an- other instance of localized thicken- ing. Here only the angles of the cells become thickened, leaving broad por- tions of the wall un- modified (Fig. 21). (a) Examples of the uniform thickening of the cell-wall may be obtained for study by making thin sections of the hard parts of many nuts and seeds (Figs. 58 to 61) ; in many of these more or less complex channels may be found. Bordered pits are best studied in longitudinal sections of the young wood of the pines, firs, Fig. 20. Young sieve tubes of Ciicurbi/a pepo The tf anr\ tlie rrnwrlprl drawing made from specimens whirh, bv having lain a etc., and the crowded !,, time in absolute alcohol, have allowed the produc- pits in the steins of tion of .xiremely clear sections; g, transverse view of tl Tji tieve-like septa ; xi, sieve plate on side wall ; aj, thin- most other Phanero- ner parts of the loagifeMjind vva i| ; ;, the same seen in o-ams Longitudinal section ; ps, contracted protoplasmic contents (lifted , off at gp from the transverse septum, still in contact sections of the stems of a ts/) ; z, parenchyma-cells between sieve-tubes, x 550. most annuals will yield -After Sachs. good examples of ringed, spiral, and reticulated thickening. The stems of the Cucurbitacese (Pumpkin, Squash, Gourd, etc.) furnish fine examples of sieve cells and collenchyma. (6) In. this place msiy be mentioned the curious and sometimes puz- 30 BOTANY. zling hernioid protrusions to be met with in some plants. When the surrounding cells are very active, it sometimes happens that the thin membrane which closes up a pit grows and is pushed through into in the lower fig- ure (Fig. 21a), where th repre- sents the thicken- ed portion of the wall, and tea the thin portion clos- ing the pits. Oc- casionally many such protrusions enter the vessel, as in a in the upper figure ;5f these be- come large they may entirely fill up the cavity of Fig. 21. Collenchyma cells of the Begonia, transverse see- fi ool oo o+ 7. tion of the petiole, e, epidermis ; e/, collenchyma-cellf, with tlie vessel, as at 0, thickened angles, r>,v, chl. chlorophyll-bodies ;p, large cell of where two large parenchyma, x 550. After Sachs. , Fig. 21a. Hernioid protrusions into the pitted vessels of ones from opposite Echfnorytti* lobata ; the upper figure magnified 250, and the sides have met. lower lOOO. From drawings by J.. C. Arthur. 36. Theories as to the Mode of Thickening. The real nature of the process in the growth in surface and thickness THICKENINGS OF THE WALL. 31 of the cell-wall was for a long time not fully understood. There have been three prominent theories advanced to ex- plain the phenomena observed. They may be briefly stated as follows : I. Von Mohl held that "the growth of the cell-membrane in thickness arises from a periodical apposition of new mem- branes upon the already completely developed wall."* Ac- cording to this theory, the marks of stratification usually seen were supposed to be the lines separating the added mem- branes. This deposition was supposed to proceed from with- out inwards ; that is, the newer layers were supposed to be placed inside of the previously existing ones ; on this ac- count this has been called the theory of centripetal thicken- ing. Until quite recently this has been the prevailing theo- ry in English and American books. II. Some observers, among whom were Hartig and Hart- ing, laying great stress upon the external markings, as seen in pollen grains, spores, etc., opposed the foregoing theory, and propounded one which has been termed the theory of centrifugal thickening. According to this theory, " the cell- membrane increases in thickness in the direction from within outwards by the deposition of layers upon the out- side of the original membrane." It is thus the exact oppo- site of the previous one ; while in the former the outer membrane is supposed to be the oldest, in the la*tter it is the inner one. III. The theory which now generally prevails is that the thickening of the wall is a growth, due to the formation or deposition of new molecules between the molecules of the original membrane. It is called the theory of intussuscep- tion, and was originated by Nageli in 1858. f * The student will find a condensed statement of this theory in the " Principles of the Anatomy and Physiology of the Vegetable Cell," by Hugo Von Mohl, translated by Henfrey, 1851. f Nageli, " Die Starkekorner," in " Pflanzenphysiologischen Unter- suchungen," 1858. Duchartre claims for Trecul the first suggestion of this theory in 1854. The term intussusception as applied to the growth of the cell-wall was used long before this ; Schleiden, in his " Contri- 32 BOTANY. 37. Every part of the living cell-wall appears, from the results of Nageli's researches, to be composed of definite molecules, which are not in contact, but separated from one another by layers of water, termed the Water of Organiza- tion. The thickness of these intermolccular layers, and con- sequently the amount of water in the whole mass of any cell- wall, v.iries in different cells, and even in the same cell. In the denser walls, or parts of walls, the water is less ; in those which are less dense it is greater. (Fig. 22.) Now it is evident that young cell-walls must have rela- tively large amounts of water in their substance, and here is where we find a growth taking place. Sachs supposes* that an aqueous solution derived from the protoplasm penetrates by diffusion between the molecules of the cell-wall. This is not a solution of protoplasm, but probably some carbohy- drate constituent of the protoplasm which is easily trans- formed into cellulose. From this nutrient solution there may be formed in the spaces filled with water new molecules of cellulose, which push aside and separate the previously formed ones ; or the previously formed molecules may be simply enlarged by the apposition of new matter. According to the theory just described, the formation of any projec- tion upon the inner surface of the cell -wall is not by the superficial deposition of molecules upon any definite area of the surface of the wall, but by tlie abundant and continued deposition of new molecules in the wall ; it consequently becomes thicker at the place of deposi- tion ; in this thickened portion still more molecules are deposited, and the thickness is further increased, and so on. In the same way projec- tions are foniie'J upon the outside of the wall by a slow internal growth. 38. Stratification of the Wall. During the increase of the cell-wall in thickness, an appearance of stratification arises in it (Fig. 23). A cell-wall in which this is strongly developed appears to be made up of concentric layers, and this no doubt gave rise to the two theories before men- butions to Phylogenesis," 1838, makes use of the word, but it may be doubted whether he or Trecul gave it exactly the meaning we now do. * " Lehrbuch," fourth edition, and the English translation of the third edition (" Text-Book of Botany "), Books I. and III. STRATIFICATION OF THE WALL. 33 tioned, in which the thickening was supposed to be due to the successive deposition of layers, either inside or outside of the original wall. It is now known that stratification is due to a subsequent change in the amount of water of organization present in partic- ular parts of the wall. When seen with the micro- scope, those layers which contain the most water, and Mr* 4-1* Fig. 22. Diagrammat.c figure to Illustrate Nagcli's the- COllSequeiltly the ory of the molecular structure of the cell-wall ; m, m, m, lpaf ppllnlnap QVO the crystal molecules ; w. w, w, the layers of water which HUbC, die separate the moli-cules. The water layers' are represented ] ofrnno-lv VP as very thin ; the v are frequently much thicker m propor- 16SS Strongly re- tjon to tne diameter8 of Se molecules. ), and then become constricted (as at c) ; the constriction deepens, and finally dhides each mass into two parts (d, e,f). 45. This may be taken, as the type of cell-formation by division, and in no case does it differ in any essential particular from this. Most plant-cells, however, are surrounded by a Avail, whose deportment during division enables us to distinguish two begun *./, completion of less well-marked modes of the P rocess.-Aftcri>e Bury, cell-form ation by division. On the one hand the wall divides as Avell as the protoplasm (Fission}, while on the other the wall takes no part in the division, and it is only the protoplasm which divides (Infernal Cell-For- mation}. 46. The best examples of Fission are to be seen in those unicellular plants which have been frequently described under the name of Protococcus.* "The cell elongates and the protoplasm divides into two across its longer axis, and Fig. 25. Division of the swarm-spores of C'fioniModer- mu di/onne ; a, with nucleus ; 6. nucleus dlMolved ; c. two nuclei, division of protoplasm ee "Huxley and Martin's Biology," Clinp. II. CELL FORMATION BY DIVISION. 3? then a partition is formed subdividing the sac ; the halves either separate at once and each rounds itself off and becomes an independent cell, or one or both halves again divide in a similar way before they separate, and so three or four new- cells are produced." 47. In many of the filamentous Thallophytes a similar fis- sion takes place, but in these the cells do not immediately sepa- rate from one another after their formation. Thus, in Nostoc and Oscillatoria (Fig. 26) the cells do not differ in any essen- tial way as to their formation from those which constitute Protococcus. In Nostoc after fission the cells round them- selves up and retain but a slight and easily separable connec- tion with one another ; in Oscillatoria, on the con- trary, the cells remain cy- lindrical and are less read- ily separable. 48. 111 SpirOUljra (Fig. Fig. M.-A, filament of Nottoe; B, filament 36, p. 45) new cells form < - x aoo.-After Prami. by the partition of old ones. The protoplasmic sac infolds all around the middle of the old cell Avhich is cylindrical in shape ; into the circular channel thus formed the cell-wall extends, appearing at first as a narrow projection from the original wall, but becoming broader and broader, until it forms a complete partition. When the new cells have elongated by intercalary growth the process of fission may be repeated, and so on.* 49. The cells which make up the greater part of the tissues of the higher plants are formed by fission. In the apical cells of Equisetum we find a curious regularity in the * The student is referred to Sachs' " Text-Book," pp. 17-18, for a further description of this process in Spirogyra ; and to Von Mohl's " Anatomy and Physiology of the Vegetable Cell," pp. 50-51, for a description of the similar fission of Cladophora glomerata (Conferva glomerata, Linn.). Von Mohl's description, which was the result of the first accurate investiga- tion of cell- formation, is erroneous in this that he supposes that during the process, to quote his words, " a cellulose membrane is deposited all over the outside of the primordial utricle" of the whole cell, and thnt it is a portion of this new membrane which forms the partition. 38 BOTANY. division. The triangular apical cells of the growing stems? divide repeatedly in the manner shown in the diagram (Fig. 27). Here the cell A B C, bounded by the heavy black Fig. 27. Diagram to show mode of fission of the apical cell, as seen from above. 7, the cell A, , C, divided by the partition 1 ; //, the t-ame cell with a second par- tition, 2 ; ///, the same cell with a third partition, 3. lines, is first divided into tAvo unequal portions by the parti- tion 1, 1. ; next the larger portion of the divided cell is again ' divided by the partition 2, II. ; later, a third partition (3, III.) is formed, and so on. It is no- ticeable that in this case the partition always forms parallel to the oldest wall of the divid- ing cell. By continued growth the apical cell retains, despite its repeated divisions, its origi- nal dimensions. 50. The growing cells of the stem of the English bean ( Vicia faba) furnish a good illustration of fission in the highest plants. In this case, and in many other, if not all, Dicotyledons, the division takec place directly through the centrally placed Fig. 28.-Meri8tem-cells of the stem of nciafaba, in procees of fission ; in the cells a, a, the process is in Us nucleus (a, Fig. 28). After the earlier st age ; at b it is completed, x . * ' , 300. After Pranti. formation of the new wall each new nucleus moves away and occupies a position on the opposite side of the cell from where it was formed (as at J and k). CELL FORMATION 7?F DTVISION. 39 (a) The foregoing; must suffice as examples of Fission. It occurs throughout the vegetable kingdom and may be regarded as the great Hieans by which cells are multiplied. (6) The cambium zone of Dicotyledons may be examined very profit- ably by the student. If a thin cross-section of a stem be soaked for a Short time in a carmine solution, the protoplasm of the cambium zone will be colored, and the newly formed partitions made thus more distinct. (c) The ends of young roots are valuable for study ; longitudinal sec- tions of these should be made, and treated as in the previous case. (d) Another interesting study of a special kind of fission may be taken up in an examination of the development of stomata. (See p. 99.) (e) That slight variation of fission, which has sometimes been called budding, may be very easily studied in the Yeast Plant (Saccharomycrs cerevmce)* The conidia, stylospores, and basidiospores of many fungi, which are more difficult to study, are very instructive examples of this va- riety of fission. Conidia may be studied in Cystopus ; stylospores in the Red Rust of the grasses (the so- called uredo-stage of Puccinia gram- inis) ; and basidiospores in young toadstools (Agaricus). 61.-Tho Yeast Plant (Sac- cliaromyces cerevisice) furnishes a VPVV snmiYIp p \-flrmiln of Tutor cells from " to P yeast;" c, bottom a \ei} simple example - yea8t after cult f va ,ion on a piece < t lial Cell - Formation. Under carrot four cells forming tatbe tote- nor of the jiarent cell ; d, the fonr Certain Conditions the Cells STOW danghter-cells ; a and b X 400, c and cl 3 , X 750. Alter Reees. to a larger size than usual ; their protoplasmic contents divide into, generally, four parts (one to four, according to Sachs), each of which rounds itself up and secretes a wall of cellulose on its sur- face (Fig. 29, c, d). Cells which divide in this way are called mother-cells, and the new ones formed from them daughter- cells. In the Yeast Plant after the daughter-cells are fully formed the dead wall of the mother-cell breaks up. 52. The terminal cells of Achlya (one of . the Sapro- leyniacece) form large numbers of daughter-cells by the breaking up of the protoplasm, as shown in Fig. 30, A. When the danghter-cells escape they become rounded (B,a); See " Huxley and Martin's Biology," Chap. I. 40 EOT ANY. after a little while they break their cellulose walls and be- come naked motile cells (/oospores) (B, e). 53. As the formation of the spores of Bryophytes and Pteridophytes, and of the pollen- cells in Phanerogams, is essen- tially alike, we may take as an example the formation of the spores of a fern (Fig. 31). The nucleus of the mother-cell first disappears, and two new nuclei \\9 \ arise P'' IL ' IIL) ; between the \^ \ I.; nuclei may be seen a line indicat- \ mi. \ lelirei ing the separation of the proto- plasmic mass into two halves. Xext the nucleus in eacli half is absorbed and replaced by two, between which a separation of the protoplasm soon takes place (IV., V.), thus dividing the cell into four equal parts, which are at first angular, but soon rounded and enclosed in cell-walls (VI., VII., VIII. , IX.). 54. In the foregoing cases the whole of the protoplasm of the mother-cell is used in the forma- tion of the daughter-cells. There are some cases, however, in which only a part of the protoplasm is Fi ? . SO.-Terminal cells of Achlya. used. One of the best known is c in the formation of ascospores. thc ^ ; Here the mother-cells are usually of the daughter cells, from which ]) A ' the nucleus disappears, and the content* have i-sciipert as motile , , . . ' , ceils (/.oos-pore^, , c, a young lat- the ])roto])lasm condenses in tlie era, branch, x 850.- After Sachs. in some cases (not in the species figured) nuclei appear, and about these portions of the protoplasm gather to form the ascospores ; in other cases (Fig. 32) the protoplasm condenses CELL FORMATION BY DIVISION. 41 about certain points without the previous formation of nu- clei (d, e). In either case firm Avails are secreted about the spores while yet in the mother-cell and surrounded by the unused part of its protoplasm. 55. The most striking example of this variety of internal cell-formation is. to be found in the development of the endosperm cells in the embryo sac of Phanerogams. The protoplasm which occupies the cavity of the embryo sac pre- sents here and there points of condensation or concentration, which in a little time become as many nuclei (Fig. 33, A, n, n), each containing a nncleolus. These nuclei are the first in- dications of the form- ing cells. Protoplasm gathers about the nu- clei and forms globu- lar or ovoid masses (A, a, a), which, after acquiring a certain size, secrete a thin Avail of cellulose on their surfaces (A, c, c', d). By the continued production of new cells within the em- bryo sac, in this Avay, they finally become crowded together into a loose tissue, in whose intercellular spaces portions of the unconsumed protoplasm yet remain (B}. After their forma- tion the cells go on increasing in numbers by simple fission Fig. 31. Development of thn pporee of Atjndium fillx-mas. /.the spore-mot her-ceil, with nucleus; //, the nucleus absorbed ; ///, two nuclei, and the division of the protoplasm into two portions ; IV, four nuclei ; V. division o the protoplasm into four portions ; VI, VII, VIII, rounding up of the young spores during the sccri-tiou of their cell-walls ; IX, mature s^pore, with thick and sculptured exospore (epispore). X 550. After Sachs. (a) Sachs f makes a strong distinction between the cases of internal cell- formation where, on the one hand, a part only, and, on the other, * The student is here referred to the account of the formation of endosperm cells in Duchartre's "Elements de Botanique," pp. 37-39 ; and also to Hofmeister's " Lehre von der Pflanzenzelle," Section 17. f " Lehrbnch," 4te auf. In the English translation of the third edi- tion all cases of fission are included under the Formation of Cells by Division of the Mother-Cell. BOTANY. the wliolf of the protoplasm of the mother-cell is used. The former he calls Free Cell Formation , and the latter Formation of Cells by Division of tlie Mother- Cell, and includes also under the last a part of what has been described above under the head of Fission. It is doubtful, however, whether such a division is of much importance. (&) What has been called the Rejuvenescence of a cell may be mentioned here. The phenomena connected with it are as follows: The proto- plasm of a cell contracts, ex- pels a portion of the water contained in it, and escapes through a slit in its wall ; the naked mass becomes for a time a free-swimming zoos- pore, after which it secretes a wall of cellulose, and begins to grow and form new cells by fission. Cases of this kind occur in CE/tloffonium, Stigeo- clonium, and many other aquatic Thallophytes. An interesting fact, but proba- bly of no great significance, is that the axis of growth of the new cell is perpendicular to that of the old one. While there can be no doubt that this process, as Sachs Fig.S8.-/totoinwtfa. A, vertical section insists* "must be regarded of i he whole plant; h, hymenium -i.e.. the layer morphologically as the for- ihwhirh the spore-forming sacs lie , (H)ll(iniun, a of the gCHUS v. _ .. ... ,, , ., 390. After cienkow- Desmidiaceae, the uniting cells have well- developed walls, and as a consequence the process is somewhat different from what it is in the Myxo- mycetes. The cells, which in this genus are two-lobed (Fig. 35), approach each other ; each sends out from its centre a protuberance which meets the other (d) ; the thin walls separating the cavities of the protuberances are absorbed, and Fig. 35. Cosmarivm MeneyMnil. a, b, c, different views of the mature plant" ; d, e, and/, three stages in the formation of the new cell ; gji, and i,thc ufter-di-vt-l- opment of the new cell. X 475. After CErstcd. the united protoplasmic masses form a round ball (e), which soon becomes enclosed in its own proper coatings (/). 58. The union of cells in SpirOffyra is much like 11, at of Cosmarinm. Here the cells arc 1 united into long filaments, CELL FORMATION BT UNION. 45 instead of being independent, as in the previous case. At the time of union the filaments approach one another and lie nearly parallel ; protuberances grow out from the contiguous cells (Fig. 36, a, b) ; their extremities meet, and the walls are absorbed, making a channel of communication from cell to cell (Fig. 36). Through this channel the protoplasm from one of the cells passes into the cav- ity of the other ; the two masses unite and form a round or ovoid cell, which soon secretes a wall of cellulose (Fig. 37, A, b, and B, c). The particular kind of union in which the two cells are of equal or nearly equal size, and illustrated above by Cos- marium and Kpirogyra, has received the name of Conjugation. It is character- istic of one group of the Thallophytes, viz., the Zygosporece. 59. In Vaucheria, a fresh-wa- ter Thallophyte, we have an ex- ample of the union of cells of very different sizes. The larger cells (called oosplieres) are in lateral protuberances of the large single cell which composes the whole plant (Fig. 38, A, and B, og). The protoplasm in these is of a spheri- cal form, and is much denser than in the main cell, from which it is separated in each case by a trans- verse Wall (shown in F\ The Fig- 36. Two filaments of Spiro- ,> >,. , . 7X gyra longata about to conjugate ; Smaller cells (the SperinatOZOiaS) at a and & are seen the protuber- , a v j.v A i 11 ances from the contiguous cells are produced by the internal cell- approaching each other, xsso.- division of the protoplasm of simi- Aft lar protuberances (the antheridia, A, and B, a). They are very small as compared with the oospheres, and are naked masses of protoplasm provided with two cilia, by means of which they are locomotive (D). Upon escaping into the water by the bursting of the old wall, they swim about, and 46 BOTANY. some of them finally reach the oosphere (through a rupture in its wall), and unite with its protoplasm (E, F). The re- sult is at once seen in its greater sharpness of outline, and in the development of a cell-wall, whereby the oosphere is transformed into an oospore. 60. Essentially the same kind of union takes place in the nearly related parasitic group, the Peronosporece. The only difference is that here the antheridium (Fig. 39, n) comes in direct contact with the oosphere (o) by means of a project- ing tube, and through this tube the protoplasm masses of the two cells unite. The absence of mo- tile spermatozoids in this case is prob- ably connected with the fact that these plants live in the tissues of land plants, instead of being immersed in water. 61. The first cell of the embryo in mosses is the result of li union of cells Pig. 37. -Filaments of the protoplasm is passing from the lower < per ; at 6 the union of tEe two protoplasmic masses is rlifferinff PTesitlv in completed ; in B the protoplasmic mae have se- C crered thick walls, thus completing the formation of size. The 1;U'"(T the new cells. X 550. After bachs. . cell lies at the bot- tom of a flask-shaped organ, the archegonium (Fig. 40, B, b) ; the smaller, the spermatozoids, are developed by the in- ternal cell-division of another organ, the antheridium (Fig. 41, -4). The spermatozoids, as in Vaucheria, are nakod masses of protoplasm, provided with cilia, by means of which they swim freely through the water (Fig. 41, B}. Upon coming in contact with the large cell in the archego- nium they fuse with it, and thus make a new cell. 62. In Phanerogams the first cell of the embryo is the re- sult of the union of the protoplasm contained in the pollen- cell with that in the embryo sac. Here again the two CELL FORMATION BY UNION. masses come in direct contact by means of a tube (the pol- len tube) which touches with its lower extremity the embry- onic vesicle. (a) The foregoing classification of the modes of cell -formation differs in many respects Irom that given by Sachs in the fourth edition of his " Lehrbuch." His classification as there given is as follows : . Fig. 3S. Vtiucheria sessilis. A, origin of the lateral branches, on (mgnnhm), and h (anttifridium), from the filament ; B, the branch a (the same as h in A) has its ter- minal portion cut off by a partition ; in ng the protoplasm is becoming greatly con- densed ; C. the same as o same moss. A^ antheridium open and permitting the ppermatozoids a to escape ; //. It. spe; ni-cell of another moss (Polytri- chum), with contained ppermatozoid ; c, .-pormatozoid free, with two cilia at the pointed extiemity. A X 850, B X 800. After Sucha. CELL FORMATION BY UNION. 49 B. FORMATION OF VEGETATIVE CELLS. 1. By the progressive formation of a division wall. 2. By the simultaneous formation of a division wall. The main objection to this classification is that its principal divis- ions are based upon physiological distinctions alone. (6) Duchartre, in his " Elements de Botanique," makes a very sim- ple classification, as follows : A. FREE CELL-FORMATION. 1. Intracellular. 2. Extracellular [Rejuvenescence]. B. FORMATION OF CELLS BY DIVISION. 1. Progressive division. 2. Simultaneous division. Note on Paragraph 56. " From the researches of Schmitz on the Myxomycetes (Sitzber. d. uieder-rhein. Ges. in Bonn, 1879), it appears that the nuclei of the cells which coalesce to form the plaemodium do not fuse, but remain distinct : this case of coalescence of cells cannot, therefore, be any longer regarded as an instance of cell-formation by conjugation." (8. H. Vines in Apn. to Sachs' Text-Book of Botany. Second English Edition, p. 945.) CHAPTER V. PRODUCTS OF THE CELL. I. CHLOROPHYLL. 63. In many plant-cells definite portions of the proto- plasm have a green color, on account of the presence of a peculiar chemical compound known as Chlorophyll.* The protoplasmic bodies thus colored are called chlorophyll-bod- ies, or chlorophyll granules, while to the coloring-matter alone, distributed in small quantity through their substance, the name chlorophyll is properly applied. 64. The chlorophyll-bodies are of various shapes and sizes. In some of the lower plants nearly the whole of the protoplasm is colored, giving the whole cell a uniform green color. In others there are stellate or band-like chlorophyll- bodies distinct from the mass of the protoplasm of the cell ; the band-like bodies are straight, or more commonly spiral (Fig. 42). In the great majority of cases, however, the chlorophyll-bodies are simple rounded granules of such mi- nute size that many are contained in a single cell (Fig. 43). The chlorophyll may be dissolved out of its protoplasmic vehicles, leaving the latter with the appearance and chemi- cal properties of ordinary protoplasm. 65. The exact chemical composition of chlorophyll is not known. As obtained by the evaporation of its alcoholic solution it is a green resin-like powder, insoluble in water. From the partial analyses of Kromayer it is probable that it contains carbon, hydrogen, nitrogen, and oxygen, and there are good reasons for believing that iron is also one of its con- stituents. * Chlorophyll is also found to a limited extent in the animal king- dom. It is present, for example, in Euglena and Hydra. CHLOROPHYLL. 51 66. With few exceptions chlorophyll is not found in cells which are not exposed to the action of light.* When ordi- nary green plants are removed for some time from the light, the chlorophyll disappears from the chlorophyll-bodies, and leaves them colorless. The same decoloration also takes place when a plant is deprived of iron as one of the constituents of its food. The disappearance of chlorophyll takes place normally in higher plants when the cells lose their activity. In the case of leaf- cells, upon the approach of autumn the chlorophyll appears to be re- moved to other portions of the plant. (a) The cells of many Palmellacere, and many swarm-spores e.g., of (Edogo- nium and Vaucheria furnish good ex- amples of the coloration of nearly the whole body of protoplasm. In Zygnema th'j chlorophyll-bodies are stellatu, and in Spiroyyr,', spiral. In Vaucheria there are multitudes of roundish or slightly angular clilorophyll- bodies, which line the interior of the large cells. The chlorophyll in the leaves of many mosses may be easily studied, even without making- sections ; in them the chlorophyll-bodies are round- ish in outline. In the higher plants thin cross-sections of the leaves afford the best means for the examination of their pjg 43. Two filaments of Spl- longata ; the chlorophyll iral bands ; in the centre . cell is a nucleus, with (b) Chlorophyll is soluble in alcohol, x^^VtSch?' protoplasm - ether, chloroform, benzine, essential and fatty oils, hydrochloric and sulphuric acids, and these may be used * The cotyledons of many Coniferae acquire a green color even in total darkness. The embryo of Phoradendron is green in the unopened seed, and in certain seeds with thick coats, which are impervious to light (e. g., in some (Jucurbitdceae), a chlorophyll -bearing layer of cells surrounds the embryo. chlorophyll-bodies, which are uniformly ro,jyra longata : the chlorophyll ... , , .. is in epiral bands ; 111 the centre of a simple rounded outline. of eacu ce ii \ 6 a nucleus, with BOTANY. for obtaining solutions. In transmitted light the alcoholic solution is green, but when viewed by reflected light it apjiears to be red. When an alcoholic solution of chlorophyll is boiled for a few minutes with an alcoholic solution of potash, and then neutralized with hydrochlo- ric acid two substances are ob- tained : the one as a yellow pre- cipitate, named Pltylloxaitthinc, and the other a blue substance dissolved in the supernatant liquid ; by evaporation the lat- ter may be obtained as a blue powder, named PJiyllocyanine. (e) The importance of iron in giving a green color to plants is easily demonstrated by grow- ing young plants of Indian corn in solutions containing no iron. The first-formed leaves are green, but subsequently only colorless ones are produced ; alter the addition of iron in the form of fen ic sulphate or ferric chloride, the colorless leaves become green in the course of a few days. The importance of light in the production of chlorophyll is shown in the etiolated shoots of the potato when grown in a dark cellar ; the same thing may be shown by germinating the seeds of many common plants in dark boxes. (d) The disappearance of chlo- rophyll is seen in the common 43 -Chlorophyll grannies in cells of operation of blanching celery the leaf of a moss, Funana fnjf/rometrica. A, f or table use, and in the blanch- granules of chlorophyll with contained starch grains, embedded in the protoplasm of the nig of grass -blades under b", granules dividing; c, d, ami e, old gran- ing such colorless plants to the tefOaFStt la&S^ lj e ht chlorophyll is produced, of chlorophyll gnmule hy the action of water. (e) Many plants which contain chlorophyll have their green color hidden by the presence of some other coloring-matter. Some- times this is dissolved in the water contained in the vacuoles ; this ia the case in Coleus, in which the dissolved pigment is red. In young plants of Atriplex the epidermal cells are filled with such a red solu- tion, hiding the green chlorophyll-bearing cells underneath. In cer- STARCH. 53 tain algae the chlorophyll-body itself contains other coloring-matters soluble in water, however in addition to the chlorophyll. Iti Floridece, (red sea-weeds) this extra coloring-matter is red ; in Fucacew, brown ; in Diatomacea, yellowish ; and iu Oscillaloriw, blue. In the degradation of chlorophyll, which takes place in the walls of the antheridia of mosses, and in the ripening of some fruitsof Phanero- gams, other colors than gre^n are produced. (/) Plants which live parasitical ly upon others, as the Dodder, and those which are saprophytic in habit, as some fungi, are usually desti- tute of chlorophyll ; where the parasitism is only partial, as in CastUlei'i and Oerardia, or where the food used (stolen) by the parasite is unas- similated,as in the Mistletoe, chlorophyll is present. In the true sapro- phytes (found mainly among the fungi) chlorophyll is never present. (g) The colors of flowers are produced in various ways. In some cases rounded masses, apparently protoplasmic in their nature, contain a red (e.g., Adonis), orange (e.g. , Zinnia), or yellow (e.g. , Cucurbita) color- ing-matter. In other cases the pigment is dissolved iu the watery fluid of the cells ; blue and violet colors are mostly produced in this way. White petals are so because their external layers of cells are fillel with air. An important difference beween chlorophyll and the pigments of flowers, is that the latter appear not to be dependent upon light for their production ; this may be shown by enclosing branches of morning- glory (lpoma. A. the youw- cells ?n their motile rtatp en- *a in the membrane of the mother-cell B, the young cells beginning to mnc themselves in a cell-family. C. the cell-family fully developed.- After Braun. adult plants are composed of single cells, but it is an embryonic condition of all others. 93. (2.) Families, or Spurious Tissues. There are some oases in which cells which are at first distinct after- wards become united more or less closely into a common mass, vhich may be denominated a Cell-Family, or Spurious Tissue. (a) Pediaitrum and Hydrodietyon furnish the best examples of true 66 BOTANY. cell-families ; in both cases separate motile cells (zoospores) in a mother- cell arrange themselves in a definite manner, and gradually unite into a family resembling the parent plant (Fig. 49). By the breaking up of the wall of the mother-cell the new family is set free. (6) In some fungi the cells composing the vegetative threads (hy- phae) unite loosely with one another into a mass. In some cases the union is so slight that the hyphae may be separated with the greatest ease, while in others it approaches' the density and firmness of true tissues (Fig. 50). While the term Cell-Family may be applied to such aggregations of cells, the common one of Spurious Tissue is to be pre- ferred * (c) In the embryo sac of Phanerogams the cells are at first separate ; Fig. 60. Rhlzomorpha subcorticalte (the compact mycelium of a fungus). The left hand flaure shows a longitudinal section of the growing end of a young shoot. The right hand figure shows a cross-section of the same ; a, the central pith-like por- tion ; o, the cortical portion of smaller cells ; A, the hairy coat, which is often wanting. X 100. After De Bary. these afterward unite into a mass which cannot be distinguished by any structural character from a true tissue. (See Fig. 33, p. 43.) As, however, the component cells were originally separate, the resulting mass must be classed with the spurious tissues. 94 (3.) Fusions. It frequently happens that the separat- ing walls of contiguous cells are absorbed and their cell- cavities merged into one. In this way long tubes (vessels) This i.-s the " Tela coutexta'' of some authors. THE AGGREGATIONS OF CELLS. 6? are formed. These may extend in any direction, but they generally run parallel to the axis of that part of the plant in which they are found. Other cell-fusions give rise to irreg- ular branching tubes, or they may even form an extended network (e.g. , in the laticif erous tissue of Cichoriaceae, Fig. 65, p. 75). 95. (4.) Tissues. A tissue may be defined as an aggre- gation of similar cells (or cell-derivatives) connately united. There are three conditions of aggregation : (a) Cell-rows. In these the cells are united by their ends into a row or filament. Such simple tissues result from cell- fission in one direction only. In some cases, as in Oscilla- Fig. 51. Succulent parenchyma from the stem of Indian corn ; transverse flection. yw, simple p)ate of cellulose, forming the partition-wall between two cells; 2,2, intercellular spaces caused by splitting of the walls during rapid growth. X 550. After Sachs. toria, the cells are short and broad, while in others e.g., Spiroyyra, Zygnema, and the hyphae of many fungi they are cylindrical or greatly elongated. Numerous cases occur in the higher plants, the most familiar being jointed hairs. (b) Cell-surfaces are composed of a single layer of cells. They result from cell-fission in two directions. Examples may be found in many Ulvaceae, and in the leaves of somo Bryophytes. (c) Masses. Where the cell-fission has been in three di- rections the result is a mass of greater or less solidity. Fre- quently, through cell-fusions, the elements which compose such masses are cell-derivatives, instead of cells ; these may be regarded as tissues of a higher order. 68 BOTANY 96. The Cell-wall in Tissues. In tic sues the walls which separate contiguous cells are at first simple and homogeneous. The plate of cellulose which first forms between two sister masses of protoplasm in cell-fission is a single one, the com- mon property, as it is the common secretion, of the proto- plasm masses. As the wall becomes older and thicker, and stratification takes place, it shows a line of separation into two halves ; this may become so well marked as actually to result in the splitting of the wall, as is the case in succulent tissues when, on account of a particular kind of tension, intercellular spaces are formed in the angles between the cells (Fig. 51). 97. By a still further differentia- tion, after a considerable thickness of the wall has been attained, there may arise a common middle lamella, which appears at first sight to lie between the original cell-walls (Fig. 52). This middle lamella, which is simply the result of a particular stratification, was long mistaken for an intercellular substance, and two pan g of thf yOTDg th 8te r iS S theories were held as to its nature. On Bec e ,io 8 n U TcS ofcTf the one hand, it was supposed to be pJrUonsTf 6 '^!*' 'x^soo- an original common matrix, in which After Sachs. t ] ie C( ,\\ s themselves were imbedded ; and on the other, it was held to be of the nature of an ex- cretion from the surrounding cells into the intercellular spaces. The first of these theories was possible only so long as the knowledge of the origin and development of cells was exceedingly defective. The second theory is rendered ex- tremely improbable by our present knowledge of the mode of growth of the cell-wall by intussusception. Until recently another view has been largely held, name- ly, that the middle lamella was to be regarded as the original common wall of the cells, and that the remaining portions were after-deposits upon it. This view gave rise to the terms Primary Cell-Avail and Secondary Cell-wall, which are still used to some extent. As this explanation of the structure rests upon the all-but-abandoned theory of the thickening THE PRINCIPAL TISSUES. of the cell-wall by the addition of successive internal layers, and is directly contradicted by the well-established doctrine of growth by intussusception, it must be regarded as erroneous. In some cases, as in the wood of Pinus sylvestris, the dif- ferentiation is so great that three lamellae are formed : (1) the common middle one, (2) an inner, and (3) an inter- mediate one. (Fig. 16, p. 26.) II. THE PRINCIPAL TISSUES. 98. There are very many kinds of tissues, distinguished from each other by characters of greater or less importance. They all, however, pass into one another by almost insensi- ble gradations ; hence by not- ing all the slight differences we may make a long list of tis- sues ; while by noting the simi- larities and gradations, all, or nearly all, the forms may be re- duced to one. The principal varieties only will be noticed in this place; each one, as here described, includes many varie- ties. 99. Parenchyma. This is the most abundant tissue in the vegetable kingdom ; it is at once the most important and the Fi?. 53 Meristem-cells of stem of faba in process of division. X most variable. As here restrict- After Pranti. ed it is composed of cells whose Avails are thin, colorless, or nearly so, and transparent ; in outline they may be rounded, cubical, polyhedral, prismatic, cylindrical, tabular, stellate, and of many other forms.* When the cells are bounded by plane surfaces, generally, but not always, the end planes lie at right angles to the longer axis of the cells. * Unfortunately, the terms parenchyma and parenchymatous have often heen restricted in meaning to tissues composed of cells whose three dimensions are equal. 70 BOTA A r. This tissue makes up the whole of the substance of many of the lower plants. In the higher plants the essential por- tions of the assimilative (green), vegetative (growing), and reproductive parts are composed of parenchyma. Instructive examples of parenchyma may be obtained in the growing ends of shoots (Fig. 53) and in the pith of Dicotyledons, in the ends of young roots t. g., of Indian corn in the green pulp of leaves, iu the pulp of fleshy fruits, and in the substance of young embryos. 10O. Collenchyma. The cells of this tissue are elon- gated, usually prismatic, and their transverse walls are most frequently horizontal, rarely inclined. With few excep- tions* there are no intercellu- lar spaces. The walls are greatly thickened along their longitudinal angles, while the remaining pans are thin (Fig. 21. p. 30). The cells con- tain chlorophyll, and retain the power of fission, f Wet specimens show by transmit- ted light a characteristic blu- ish white lustre (Figs. 54 and 55). Colleuchyina is found be- neath the epidermis of Dico- tyledons (and some ferns). usually as a mass of conside- rable thickness, and is doubtless developed from parenchyma for the purpose of giving support and strength to the epi- dermis. F5g. 54. Trans yerse section of collen- chj-ma (00) of the stem of R'hinocyttu lobata. wet with water, and the arigks jrrcatly swollen. ei>. epidermis, with thickened outer wall x TOO. " drawing by J. C. Arthur. From a * In the eollenrliyma of SilpMum pfrfoliatum there are many lon- gitudinal intercellular spaces of various sizes ; in fptnmrn purptirea there are minnte ones. f De Bary states that collenchyma-oells are capable of fission. ' Verjjleichende Anatomit- dr r VegetatiousorgaDe der Phauerogam. n und Faroe," p. 126. TIIE PRINCIPAL TIMUE8. 71 (a) Collenchyma may be studied in the stems, petioles, and leaf-ribs of herbaceous Dicotyledons e.g., in species of fyttpfdum, Rheum, Rums.x, Chenopodium in many Labiate, txdanacece, Begoniaceoe, Gu. curbitacece, and many others; also in the petioles of the water-lilr and young stems of the elder. (6) Upon soaking in water, or upon treatment with nitric or sulphu- ric acid, the thickened angles become greatly swollen. Fie. 55. Longitudinal radial section of stem of EcJiittocystit tobala. ep, epidermic ; oo, collenchvma ; pa, parenchyma : /, a single wood fibre, marked with " crossed " (i.e., twisted) piu> ; tji, intercellular spaces, x 500. Prom a drawing by J. C. Arthur. (e) Upon treatment with Schultz's Solution the thickened angles are colored light blue. (d) Upon slight warming in a solution of ix>tash, and then treaties with a solution of iodine in potassium iodide, the thickened angles be- come colored dark blue. 1O1. Sclerenchyma. In many plants the hard parts are composed of cells whose walls are thickened, often to a very 72 BOTANY. considerable extent. The cells are usually short, but in some cases they are greatly elongated ; they are sometimes regular in outline, but more frequently they are extremely irregular. They do not contain chlorophyll, but in some cases at least (e.g., in the scleienchyma-cells in the pith of apple-twigs) they contain starch. Sclerenchyma occurs in Bryophytes, Pteridophytes, and Phanerogams. (a) Good specimens of sclerenchyma may be obtained for study by making longitudinal sections of the rhizome of Pteris aquilina, in Fio. 565. FIG. 56^4. Fio. 57. Fig. 56. Two eclerenchyma-cells from the hypoderma of the rhizome of Pteris aquilina, isolated by Sclmtze's maceration. A, a very thick-walled cell, with branch- ing pits; B, a cell with walls less thickened the wall of the opposite side of the cell is seen to be filled with numerous pits. X 500. After Sachs. Fig. 57. Margin of leaf of PinusjAnaster, transverse section, c, cuticularized layer of outer wall of epidermis ; i, inner non-cuticularized layer ; c', thickened outer wall of margin il cell ; g, i', hypoderma of elongated s lerenchyma ; j>, chlorophyll- bearing parenchyma ; pr, contracted protoplasmic contents, x 800. After Sachs. which it occurs as a thick hypodermal mass ; by boiling in potassium chlorate and nitric acid (Scliulze's maceration) the cells may be com- pletely isolated (Fig. 56, A and B). (b) The cells of the medullary rays of woody Dicotyledons e.g., Acer, Pirus, Ostrya, Liriodendron, etc. are generally thick-walled when old. and in this state must be classed as sclerenchyma. (c) The hypoderma of the leaves of pines consists of elongated scle- nmchyma-cells, which at first sight might easily be mistaken for bnst fibres (Fig. 57, rj, ). The hypoderma of many other plants appears to be of a similar nature. THE PRINCIPAL TISSUES. 73 (d) The bard tissues of nuts and of stone fruits furnish excellent ex- amples of short and very thick- walled sclerenchy ma-cells. In the hickory nut (Carya alba) the cells (Figs. 58 and 59) are not more than Fig. 58. Sclerenchyma-cells of the shell (endocarp) of the hickory-nut (Carya alba), taken parallel to the surface of the nut. X 400. Fig. 59. Sclerenchyma-cells of the shell (endocarp) of the hickory-nut (Carya alba), taken at right-angles to the surface of the nut. X 400. two or three times as long as broad, and the thickening is so great as almost entirely to obliterate their cavities; the thickened walls are fee. Fro. 61. Fig. 60. Sclerenchyma cells of thv seed-coat of Echinocystis lobata, from a section at right angles'to the surface of the seed ; a, a cell cut directly through its centre. showing the whole of the cavity the three dark spots are probably oil ; b, a cell cut through at one side of the middle ; c, a cell whose cavity was not cut into in making the section. X 250. From a drawing by J. C. Arthur. Fig. 61. Sclerenchyma-cells of the seed-coat of BdHnocygfts lobala, from a section parallel to the surface of the seed, x 250. From a drawing by J. C. Arthur. pierced by many deep pits. The cells are arranged with their longer axes perpendicular to the surface of the nut, and are very closely packed together. 74 BOTANY. (e) The seed-coat of Echinocystu lobata is composed almost entirely of sclerenchyma (Fig. 60). The cell-walls are greatly thickened, and the cells are very closely packed together, so much so that all are sharply prismatic (Fig. 61). 102. Fibrous Tissue. This is composed of elongated, thick-walled, and generally fusiform elements, the fibres (Figs. 62 and 63), whose walls are usually marked with simple or sometimes bordered pits. These elements in cross- section are rarely square or round, but most generally three to many-sided. They are found in, or in connection with. the fibro-vascular bundles of Pteridophytes and Phanero- gams,and give strength and hardness to their stems and leaves. PIG. 62. Fio. 63. Fip. 82. Wood fibres of Acer dcuycarpum. isolated by Schulze's maceration, a, four fibres, x 95 ; b, a portion of a fibre, x 230, showing the diagonally placed elon- gated pita ; c, the ends of eleven united fibres. X 95. Fig. 63. Bast fibres of Acer dasycai~pym, isolated by Schulze's maceration, a, a fibre, x 96 ; 6, a portion of a fibre, X 230, showing the much-thickened wall. Two varieties of fibrous tissue may be distinguished, viz., (1) Bast (Fig. 63), and (2) Wood (Fig. 62). The fibres of the former are usually thicker walled, more flexible, and of greater length than those of the latter. In both forms the fibres are sometimes observed to be partitioned.* * These partitions liave generally been considered as formed subse- quently to the fibres ; but it may well be questioned whether, in some THE PRINCIPAL TISSUES. T5 To examine fibrous tissue it is only necessary to make thin longitudi- nal slices of the stems of woody plants e.g., Acer, Pirus, etc. and to heat for a minute or less in nitric acid and potassium chlorate. The FIG. 64. FIG. 65. Fig. 64. Laticiferous tubes from Euphorbia. A, moderately magnified; B. more highly magnified, and showing the bone-shaped or dumb-bell-shapea starch grains. Fig. 65. Laticiferous vessels of Scorzonera hispanica. A , a transverse section of the phloe'm of the root ; B, the same more highly magnified. After Sachs. fibres may now be separated under a dissecting microscope, or the cases at least, the fibres are not cell-derivatives, and the partitions the persistent walls of the original component cells. BOTANY. specimens may be transferred to a glass slide and dissected by tapping gently upon the centre of the cover-glass. 103. Laticiferous Tissue. In many orders of Phanero- gams tissues are found whose component elements contain a milky or colored fluid the latex. To these, although vary- ing greatly in structure and position, the general name of Laticiferous tissues has been given. For the sake of simpli- city two general forms may be distinguished : (1) that composed of simple or brandl- ing elements (Fig. G4), which are scattered through the other tissues. As found in EupliorbiacecB, Avhere they oc- cur in parenchyma, they are somewhat simply branched, and have very thick walls (Fig. 64, B) ; in other orders they are thin walled and are sometimes inclined to anasto- mose. From their position it is quite certain that the ele- ments of this form of laticif- erous tissue frequently replace bast fibres. In such cases they are said to be metamor- Fig. 66 Laticiferous cells of the onion, J . from a longitudinal section of a scale of pllOSed bast fibres I* 111 other the bulb. , epidermis with cuticle c ; p, , ., parenchyma ; sg, coagulated contents of CaSCS, however, they appear laticiferous cells, contracted so as to show , v r . i -, the porous walls; g, g, transverse wall.- not to be of this nature, but to arise from the parenchyma by the absorption of the horizontal partition- walls, f * There is an objection to the word metamorphosed in this connec- tion, as it does not exactly express the relation between the laticiferous elements and the bast fibres. It must not" be understood that the former are made by a transformation of the formed bast fibres ; the relation is rather that they develop from what under other circum- stances would have developed into bast fibres. We may express the relation by saying that laticiferou.3 elements and bast fibres are closely related sister elements. f " According to Hanstein, it is probable that in some Aroideae vessels THE PRINCIPAL TISSUES. 77 (2.) The other form is that composed of reticulately anas- tomosing vessels. Here the tissue is the result of the fusion of great numbers of short cells. The walls are thin and often irregular in outline. In Cichoriacece this form of laticiferous tissue is very perfectly developed as a consti- tuent part of the phloem portion of the fibro-vascular bundles (Fig. 65, A and B}. (a) Laticiferous tissue has not yet been shown to contain either pro- toplasm or nucleus.* The latex is an emulsion of several substances, some of which, as caoutchouc (India-rubber), gutta-percha, and opium, are of great economic importance. In some cases, as in Euphorbia, grains of starch are contained in the latex (Fig. 64, B). (b) The chemical composition of latex is shown by the following analyses, as given by De Bary : f Latex of Hevea Ouianensis, as determined by Faraday : Water with an organic acid 56.3 per cent. Caoutchouc 31.7 " Albumen 1.9 " Bitter nitrogenous matter, with wax 7.1 " Residue soluble in H a O,butinsoluble in alcohol. 2.9 " Latex of Galactodendron utile, as determined by Heintz : Water 57.3 per cent. Albumen 0.4 Wax (C 3 5 H 68 O 3 ) 5.8 Resin (C 3 5 H 68 O a ) 31.4 Gum and sugar 4.7 Ash 0.4 100. Latex of Euphorbia cyparissias, determined by Weiss and Wiesner Water 72.1 per cent. Resin 15.7 Gum 36 Sugar and extractive substances 4.1 Albumen 0.1 Ash 0.9 96.5 of the xylem assume the form and function of laticiferous vessels.' Sachs' " Text-Book of Botany," English edition, p. 110. * The latex of some Cichoriacese coagulates much like protoplasm , possibly further investigation will show it to be present. f "Anatomic der Vegetationsorgane," etc., p. 194. 78 BOTANY. (c) Examples of the simpler forms of laticiferous tissue may be ob- tained for study from Euphorbiacece, Urticacea, Asclepiadacea, Apocy- nacece. Forms less simple occur in Aracece, and in the maple ; in the last-mentioned they appear to replace the sieve-vessels. Related to these again are the peculiar milk-vessels of the onion (Fig. 66), which consist of elongated cells separated by thin or perforated septa. Fig. 67. Longitudinal section through the sieve tissue of Cucurbita Pepo. g, q, section of transverse sieve - plates ; si, lateral sieve-plate ; as, thin places in wall ; /, the same seen in section ; ^w, protoplasmic contents contracted by the alcohol in which the speci- mens were soaked ; ep, pro- toplasm lifted off from the sieve-plate by contraction ; si, protoplasm still in con- tact with the sieve-plate ; z, parenchyma between sieve tubes. X 550. -After Sachs. (rf) The more complex or reticulated forms of laticiferous tissue occur in dchoriacm, Campanulacea, Lobdiaceoi, Convolvulacea, Pn- (e) By heating thin sections of any of the foregoing plants in a di- lute solution of potash the laticiferous tissues may be readily isolated for study. (/) The walls of the laticiferous elements are always rich in water, and are composed of cellulose, as may be shown by the blue coloration which follows treatment with Schultz's Solution. TUE PRINCIPAL TISSUES. 104. Sieve Tissue. As found in the Angiosperms this tissue is made up of sieve ducts and the so-called latticed cells. The former (the sieve ducts) consist of soft, not lignified, colorless tubes of rather wide diameter, having at long intervals horizon- tal or obliquely placed perforated septa. The lateral walls are also perforated in restrict- ed areas, called sieve discs, and through these perforations and those in the horizontal walls the protoplasmic contents of the con- tiguous cells freely unite (Figs. 67 and 68). In many plants the sieve discs close up in winter by a thick- ening of their sub- stance (Fig. 69). The tissue composed of these ducts is gene- rally loose, and more or less intermingled with parenchyma ; in some cases even single ducts run longitudin- ally through the sub- stance of other tissues. Fig. 68. Longitudinal tangential section of the young bark of the grape (Wis tin if era), taker the beginning of July. $, s, sieve tubes, with i Jll the form described ti n sof the transverse plates iu the left-hand sie ., . . , tube, at the top of the figure a lateral plate is It IS found OnlV shown ; t, m, medullary rays, with crystals in ,1 " some of the cells between the sieve tabes them- One Ot the COmpO- selves, and between them and the medullary rays, fa n-t +1 1,1 a e masses of parenchyma iphloem purenchyma) the phloem X 145.-Aftcr]JeBary. portion of the fibro- vascular bundle. 105. The so-called latticed cells ar3 probably to be 80 BOTANY. regarded as undeveloped sieve ducts, and hence the tissue they form may be included under sieve tissue. Latticed cells are thin-walled and elongated ; they differ from true sieve ducts principally in being of less diameter, and in having the markings but not the perforations of sieve discs. Both of these differences are such as might be looked for in un- developed sieve tissue. 1O6. In the corres- ponding parts of the vas- cular bundles of Gymno- sperms and Pterido- phytes a sieve tissue is found which differs somewhat from that in Angiosperms. In Gym- nosperms the sieve discs, which are of irregular outline, occur abundant- ly upon the oblique ends and radial faces of the Fig L 69. - Longitudinal broad tubes (Fig. 70). " Io the g f rap h e! In Pteridopliytes the Ve^niate * tubes have varying forms ; in Equisetum After DC Ba7 y r' ' an( j Qphioglossum they are prismatic, with numerous horizontal but not vertical sieve discs ; in Pteris and many other ferns they have pointed extremities, and are greatly elongated, bearing the sieve discs upon their sides (Fig. 71). In the larger Lycopodiaccm the sieve tubes are pris- matic and of great length ; in the smaller species there are tissue elements destitute of P |a tf s repia< . erally and are corn- Sieve discs, but which are otherwise, mclud- posed of many utiie ... . ,, ,, ,., ., punctured areas ing position in the stem, exactly like the grouped together ir- sieve ducts of the larger species. A^ei^e'Bary. (a) Good specimens of sieve tissue may be obtained for study by making longitudinal sections of the stems of Cucurbita, Cucumis, THE PRINCIPAL TISSUES. 81 Eehinocystis, Ecbalium, Vitis, Bignonin, and Calamus Rotang ; also Abies pectinatff, Larix, Juniperus, Sequoia, and Ginkgo ; also Pteris, Osmunda, Equisetum, and Lycopodium. (6) By making repeated horizontal sections the horizontal sieve discs may be found and studied. (c) Alcoholic specimens afford much more satisfactory results than fresh ones ; especially is this the case with the more succulent plants. Pig. 71. Sieve tissue of Pteris aquilina. A, end of a sieve tube isolated by macer- ation; B. portions of two tubes seen in vertical section ; in ' the sieve plates are Keen in front view ; at c, c, they are seen in section ; the tube s 2 has sieve plates on its right and left walls, but none on its further wall, which is in contact with pa- rcnchyma-cdls ; two of the latter are seen to have nuclei in them, x 375. After i)e Bary. 1O7. Tracheary Tissue. Under this head are to be grouped those vessels which, while differing considerably in the details, agree in having thickened walls, which are perfo- rated at the places where similar vessels touch each other. The BOTANY. thickening, and as a consequence the perforations, are of various kinds, but generally there is a tendency in the former to the production of spiral bands ; this is more or less evident even when the bands form a network. The transverse parti- tions, which may be horizontal or oblique, are in some cases perforated with small openings, in others they are almost or entirely absorbed. The diameter of the vessels is usually considerably greater than that of the surrounding cells and elements of other tissues, and this alone in many cases may serve to distinguish them. When young they of course con- tain protoplasm, but as they become older this disappears, and they then contain air. 108. Tracheary tissue is found only in Pteridophytes Fig. ~2. Longitudinal section of a portion of the stem of Impatient Bakumina. n. a ringed vessel : i/, a vessel with rings and short spirals ; ?;", a vessel with two spirals ; v"' and v"", vessels with branching spirals ; -t""\ a vessel with irregular thicken- ings, forming the reticulated vessel. After Duchartre. and Phanerogams. The principal varieties of vessels found in tracheary tissues are the following : (1.) Spiral Vessels, which are usually long, with fusiform extremities ; their walls are thickened in a spiral manner with one or more simple or branched bands or fibres (Fig. 72, v", v'", v""). This form may be regarded as the typical form of the vessels of tracheary tissue. In most cases the direction of the spiral is from right to left.* It is frequent- ly in one direction in the earlier formed spirals and the op- * Right to left, in speaking of these spirals, as also in describing the twining of certain climbing plants, is passing up and around in the di- rection of the hands of a watch. Left to right is of course up and nround opposite to the hands of a watch. THE PRINCIPAL TISSUES. 89 posite in those formed later ; while in interrupted spirals both directions occur in the same vessel. Ringed and reticu- lated vessels are opposite modifications of the spiral form : A Fig. 73. Scalariform vessels of the rhizoma of Pteris aqtiilina. A, longitudinal sec- tion of an end (about one third of the whole) of a short vessel ;/, the fusiform ex- tremity, with long pits placed transversely; B, a small portion of A, taken from x, and much more highly magnified ; C\ a longitudinal section of a portion of the side wall between two vessels : D, a similar section through the inclined end wall (A.f) ; in the upper-part of D, at/ the wall between the thickening ridges is broken through. A, X 142 ; the others X 375.-Af ter De Bary. the first are due to an under-development of the thickening forces in the young vessels, resulting in the production here and there of isolated rings (Fig. 72, v) ; reticulated vessels are due, on the contrary, to an over-development, which KOTANY. gives rise to a complex branching and anastomosing of the spirals (Fig. 72, v'""). (2.) Scalariform vessels. These are prismatic vessels whose walls are thickened in such a way as to form transverse ridges, as described in paragraph 32, page 28. They are wide in transverse diameter and their extremities are fusiform or truncate (Fig. 73). (3.) Pitted Vessels. The walls of these vessels are thickened in such a way as to give rise to pits and dots, as described in paragraph 31, page 26. The vessels are usually of wide diameter; in some forms they are crossed at frequent intervals by per- Fis. 74. FIG. 75. Fig. 74. Pitted vessels of Artntolochla stp'io, from a longitudinal section of the stem ; the vessel on ihe right is seen in section, that on tin- left from without ; ha. o, epidermis ; 8, walls beiween air-spaces, the latter filled with rows of chloro- phyll-bearing cells, chl ; sp, a stoina ; y, a large parenchyma-cell. X 550. After Sachs. there is an epidermal system of a high degree of perfection, and composed of epidermis proper and stomata (Fig. 78). The epidermis consists of a single layer of somewhat tabu- lar cells arching over the air-cavities which occupy the upper surface of the plants ; it is perforated here and there by sto- mata or breathing pores, composed of four to eight circular rows of cells placed one above the other (sp in the figure). These chimney-like structures originate by the division of a single cell into four or six radiating daughter-cells ; in the centre of this group an intercellular pore is formed by the lateral growth of the cells (Fig. 79) ; and by a subsequent 92 BOTANY. horizontal division the several superimposed circular rows of cells are formed. 120. In true mosses the sporangia possess an epidermal system which is composed of a layer of strongly cuticular- ized cells the epidermis sometimes provided with stomata. Other portions of the plant, aside from the sporangia, are destitute of a true epidermis or of stornata. 121. The epidermal systems of Pteridophytes and Phaner- ogams are so much alike that they may be described together, although it must be remembered that in the latter group they are, in general, somewhat more perfect than in the for- mer. In these groups the epidermal structures consist usually of three por- tions : (1) a layer of more or less modified parenchyma the epidermis proper bearing two other kinds of structures which develop from it, viz., (2) trichomes, and (3) stomata. 122. Epidermis. The differentia- tion of parenchyma in the formation of epidermis, when carried to its ut- most extent, involves three different modifications of the cells, viz., (1) change of form, (2) thickening of the &**?%**$% walls, (3) disappearance of the proto- reSgmthTarge?; plasmic contents. These three modi- a, guard-ceils After Sachs, fications may occur in varying de- grees of intensity ; they may all be slight, as in many aquatic plants and in the young roots of ordinary plants ; or the cells may change their form, while there may be little thickening of their walls, as in other aquatic plants, and some land plants which live in damp and shady places ; or on the other hand, the change of form of the cells may be but little, while their walls may have greatly thickened, resulting in a disap- pearance of their protoplasm, as may be seen in parts of some land plants which grow slowly and uniformly. When the differentiation of epidermis is considerable, it can usu- ally be readily removed as a thin transparent sheet of color- less cells, TUB, EPIDERMAL SYSTEM. 93 123. The change in the form of the epidermal cells is due to the mode of growth of the organ of which they form a part; the lateral and longitudinal growth of an organ causes a corresponding extension and consequent flattening of the cells ; if the growth has been mainly in one direction, as in the leaves of many Monocotyledons, and the young shoots of many Dicotyledons, or if the growth in two direc- tions has been regular and uniform, as in the leaves of some Dicotyledons, the cells are quite regular in outline ; where, however, the growth is not uniform the cells become irregu- lar, often extremely so (Fig. 89, page 100). 124. The thickening of the walls is greatest in those plants and parts of plants which are most exposed to the dry- ing effects of the atmospheie. It consists of a thickening of the outer walls, and frequently of the lateral ones also. The outer portion of the thickened walls is cuticularized, and this, by a subsequent stratification and lamellation, is separ- ated as a continuous pellicle, the so-called cuticle. 125. The cuticle extends uninterruptedly over the cells, and maybe readily distinguished from the other portions of the outer epidermal walls. It is insoluble in concen- trated sulphuric acid, but may be dissolved in boiling caustic potash. Treated with iodine it turns a yellow or yellowish brown color. A waxy or resinous matter is fre- quently developed upon the surface of the cuticle, constitut- ing what is called the Uoom of some leaves and fruits. De Bary* distinguishes four kinds of waxy coating, as follows : (1) continuous layers or incrustations of wax e.g., on the leaves and stems of purslane, the leaves of Fuchsia, yew, the stems of the wax palms (Ceroxylon], etc. ; (2) coatings com- posed of multitudes of minute rods placed vertically side by side upon the cuticle e.g., on the stems of sugar cane, Coix lachryma, and some other grasses ; (3) coatings made up of minute rounded grains in a single layer e.g., on the leaves of the cabbage, onion, tulip, clove-pink (Dianthus * " Vergleichende Anatomic der Vegetationsorgane der Phaneroga- men und Fame," 1877, p. 87, where figures of several of these kinds are given. 94 BOTANT. Caryophyllus), etc. ; (4) coatings of minute needles or grains irregularly covering the surface with several layers e.g., on the leaves of Eucalyptus globulus, rye, etc. 126. The protoplasm of the epidermal cells generally disappears in those cases where there is much thickening of the walls ; it is always present in young plants and parts of plants ; it is also frequently present in older portions, which are not so much exposed to the drying action of the atmos- phere, as in roots, and the leaves and shoots of aquatic plants, and of those growing in humid places. In few cases, how- ever, are granular protoplasmic bodies (e.g., chlorophyll) pres- ent in epidermal cells.* 127. AVhile the epidermis always consists at first of but one layer of cells, it may become split into two or more lay- ers by subsequent divisions parallel to its surface. These layers may resemble the outer one and have their walls thickened, as in the leaves of the Oleander, or they may con- sist of thin-walled cells with watery contents (constituting the so-called Aqueous Tissue), as in the leaves of Ficus and Begonia. (a) Epidermis may be studied with comparatively little difficulty. In many cases it may be stripped off in thin sheets and mounted in the usual way ; such preparations, with thin cross-sections (which are readily made by placing a piece of leaf between pieces of elder pith), are sufficient, in most cases, to give a good knowledge of the structure. The leaves of many Liliacfce (hyacinths, lilies, etc.) and Graminece may be examined for regular cells, and those of many Dicotyledons, as bal- sams, primroses, and fuchsias, for irregular ones. (6) Thickened epidermal walls may be found in leaves of a hard tex- ture, as those of the pines, holly, oleander, mistletoe, many Composite, and in the stems of many Cactace.ce. The stratification of the thickened walls may be brought out in the cross-sections by heating in a solution of potash. (r) A series of specimens of the epidermis, taken from leaves of all ajjes.from their youngest and smallest rudiments in the bud up to full- grown ones, is instructive. * In the leaves of Primula sinen&is, grown in the green-house, the epidermal cells contain many chlorophyll-bodies ; the leaves of Fuchsias, under similar conditions, possess a few chlorophyll-bodies in the epider- mal layer. THE EPIDERMAL SYSTEM. 95 128. Trichomes. Under this term are to be included the outgrowths which arise from the epidermis ; they may have the form of hairs, scales, glands, bristles, prickles, etc., and may be composed of single cells, or of masses of cells. They originate mostly from the growth of single epidermal cells,* and on their first appearance consist of slightly en- FIQ. 81. Fia.80. Pig. 80. Transverse section of epidermis and underlying tissue of ovary of Cu- cwtota. a, hair of a row of cells ; b and d, glandular hairs of different ages ; ,/, c, hairs in the youngest stages of their development. X 100. After Prantl. Fig. 81 A seedling mustard plant with its single root clothed with root -hairs ; the newest (lowermost) portion of the root is not yet provided with root-hairs. larged and protruding cells (Fig. 80, e, f, c). These may elongate and form single-celled hairs, which may be simple or variously branched. The most important of these hairs are those which clothe so abundantly the young roots of most of the higher plants, and to which the name of Root-hairs * It is probable that the common statement that trichomes al ways develop from single cells must be modified. 96 &OTANY. has been applied (Fig. 81). These are composed of single cells, which have very thin and delicate walls (Fig. 82), and are the active agents in the absorption of nutritive matters for the plant. i Fig. 82. -Root-hairs of a seedling rye plant. A, the ends of three haire, one much cinallcr th in the others ; the larger ones have particles of sand adhering to and im- bedded in their walls ; , the base of a hair growing from the root-cell, r. X 900. 129. In the development of the hairs on aerial parts of plants it frequently happens that the terminal cell becomes changed into a secreting cell, in which gummy, resinous, or other substances are produced ; sometimes several terminal THE EPIDERMAL SX8TMH. cells are so transformed into a secreting organ, tion appears as a rounded pustule, partly surround- ing the secreting cell (Figs. 83 to 87), and which is removed upon the slightest touch. Tri- chomes of this nature are called glandular hairs ; they are exceedingly vari- able in form, and are not infrequently short and depressed, when they are known as surface glands, or glandular scales (Fig. 87). The secre- Glandular hairs from the petiole of o, sinensit, in several stages of deyelop- (ft\ Triehomes are in p-ene ment. a, the beginning of the secretion iu the are, in gene- termina , ce]1 . b hair ith a j mags of ge . ral, easy objects of study, creted matter ; d, an old hair after the removal In many cases they may be of the secreted matter, x 142.-After De Bary. simply scraped off and mounted in alcohol, or in a solution of potash FIG. 84. FIG. 85. FIG. 86. FIG. 87. Fig. 84. -a', the cell a of Fig. 83 more highly magnified ; a" the same after removal of the secretion by treatment with alcohol, x 87.5. After De Bary. Fig. 85 c, end of a hair with large mass of secreted matter ; c', the same after treatment with alcohol, x 375. After De Bary. Fig. 8(5. The end of the hair (I, in Fig. 83. more highly magnified, showing the frag- ments of the secretion pustule surrounding the terminal cell, which still contains pro- topjasm X 375 After De Bary. Fig. 87. Glandular scale from the hop. A, in its young stage ; B, the same some time afterward the secretion from the cells has pushed out the cuticle and filled the space between it and tho cell* (in the specimen from which these were drawn the secretion was removed by solution in alcohol). X 142. After De Bary. after wetting them with alcohol to free them from entangled and en- closed air. BOTANY. (b) One-celled simple hairs may be obtained from the vegetative organs of species of (EnotJiera and Brassica and many grasses e.g., species of Panicum and from the seeds of the cotton plant ; the last constitute the ' ' cotton" of commerce. (c) Many-celled simple hairs occur on the filaments of Tradescantia, on leaves of the Primrose, Ageratum, Erigeron Canadense, pumpkin, and very many others. (d) Branched one-celled hairs occur in Capsclla, Draba, Sisymbryum, Alyssum, and many other Cruciferw. (e) Branched many-celled hairs may be found on the Mullein and Ivy. Vis- 88. Hairs from Thistle (Otiicus altiitsimiix). j, young hniir from the stem before it has been drawn out ; S, an older hair more highly magnified, after its ex- tremity has been drawn out into a thread-like la*h ; C, hair with a long laeh from i he underside of a full-grown leaf. Highly magnified. After Heal. (/) Clustered or tufted hairs are found on many Malvacew, and the nearly related scales or peltate hairs on SJicpherdia. ((/) Root-hairs are btst obtained for study by growing seeds of mustard, radish, wheat, etc., on damp cotton or blotting-paper, and then mak- ing careful longitudinal sections of the terminal portion of the root at the place where the hairs are just appearing (usually several millimetres above the tip of the root). By making preparations in this way all stages of the development of these hairs may be studied in the same specimen. (h) Glandular hairs are found in many groups of plants ; they may be studied in Petunia, Verbena, Primula, Martynia, and the tomato. (i) Apparently related to glandular hairs are the curious hairs from THE EPIDERMAL SYSTEM. 99 which, as pointed out by Professor Beal,* are drawn out the long thread-like lashed which are so abundant on the leaves of some thistles and other Composite (Fig. 88). These lashes appear to be of the na- ture of secretions, and they are capable of being drawn out to an aston- ishing length. These are, in turn, much like the glandular hairs on the leaves of Dipsacm sylvestris, discovered by Francis L>arwin,f and from which motile protoplasmic filaments protrude. Mr. Darwin concludes that they have the power of absorbing nitrogenous matter. 130. Stomata (singular, Stoma). These structures con- sist, in most cases, of two specially modified chlorophyll- bearing cells, called the Guard-cells, which have between them a cleft or slit passing through the epidermis (Figs. 89, 90). These openings are always placed directly over interior intercellular spaces. Stomata are developed from, and in their distribution always have a relation to, the epidermal cells; in an epidermis composed of regular cells there is more or less regularity in the arrangement of the stomata ; but when the epidermal cells are irregular the stomata are also irregularly placed. They occur on aerial leaves and stems most abundantly, being sometimes exceedingly numerous, and are exception- ally found on other parts, as the sepals, petals, and carpels of the flowers. On submerged or underground stems and leaves they are found in less numbers, and from true roots they are always absent. The stomata on leaves are generally confined to the lower surface, and when present on the up- per they are usually much fewer in number ; there are, how- ever, some exceptions to this. 131. Their development generally takes place in the fol- lowing way : in a young epidermis-cell a partition forms at right angles to the plane of the epidermis, cutting off a por- tion of the cell ; this in one series of cases becomes the mother-cell of the stoma ; in another series of cases, how- ever, it is divided one or more times by subsequent partitions before the mother-cell is formed. In either case, when once * In an article entitled " How Thistles Spin," in the American Nat- uralist, 1878, page 643. See also an article by the same writer on ' Hairs and Glandular Hairs of Plants : their Forms and Uses," in the same volume of the journal named, on page 271. f See his account, with a plate, in Qr. Jour, of Mlc. Science, 1877, p. 245. 100 BOTANY. the mother-cell is formed a median partition- wall forms in it, and gradually becomes separated into two plates, which eventually sepa- rate and form a pore through the epidermis. The two halves of the mother-cell be- come symmetrical- ly rounded off into semilunar or semi- circular forms, and constitute the guard-cells before mentioned. The details of the fore- going process in one of its more complex forms are illustrated in Fig. 91, A and B. The splitting of the middle partition-wall of the mother-cell is shown in the successive sections (Fig. 92). 132. In the light, under certain conditions of moisture and temperature, the guard-cells become curved away from each other in their central portions, thus opening the slit and allowing free communication between the external air and that in the in- , Fig. 90. Double *tomata from the under surface tercellular Spaces and of the leaf ol 'Echlnocystls lobata. xSOO.-Fromi passages of the leaf. Fig. 89. Stomata from the under surface of the leaf of Echmocystis lobata. s, s. stomata ; g, g, irregular epider- mis-cells between the veins of the leaf ; v, elongated and regular epidermis-cells over a vein. X 250. From a drawing by J. C. Arthur. drawing by J. C. Arthur. (a) A superficial examination of stomata may be easily made by stripping off the epidermis, and mounting it in water or alcohol. Good sections of stomata are more difficult to make ; they may be obtained, Tig. 91. The development of the ftomata of the leaf of Sedum purpurasctm. A , a piece of very young epidermis, showing the early stages of tlie process. The nu- merals indicate the order of formation of the partitions ; that marked 1, 1, 1, was formed first, then 2, 2, and last 3, 3 ; the cell enclosed by thesie three partitions is the stoma-mother-cell ; B. a fully completed stoma ; e, e, two original epidermis-cells in the right hand one the new partition 1, 1, 1. first appeared ; this was followed by i, S. 2, then by 3, 3, and 4, 4 ; ".asily tho cell thus formed bee >me divided l>y a middle partition, which Boon split, and thus formed the opening of the stoma. After Sachs. FIG. 92i). FIG. 92n. Fig. 92. Development of thestomata of the leaf of Hyacinthu* orientalls, seen in transverse section. A, the division of the mother-cell S; e, e, epidermis-cells ; p, , parenchyma-cells ; i, small intercellular -pace ; B and C, the sanie a little later ; i, first separation of the two guard-cells by the splitting of the partition between them, forming the opening t ; E, the fully formed stoma. x 800. After Sachs. 102 BOTANY. however, by making a large number of very thin sections of the whole leaf (by placing it between two pieces of elder pith), when it will be found that in some cases stomata have been cut through in the man- ner shown in Fig. 92. (6) Examples may be obtained from any of the higher plants, but those which are of a firm texture and have a smooth epidermis are best to begin with e.g., the hyacinth, tulip, the lilies, many grasses, fuchsia, lilac, etc. (c) Weiss* determined the number of stomata on the epidermis of both surfaces of 167 leaves of plants ; some of his results are given below: In one square millimetre. In one square inch. Upper side.' Under side. Upper side. Under side. 175 138 55 60 101 67 114 94 184 89 50 65 48 625 477 461 386 380 325 302 278 270 263 259 251 237 229 216 208 204 191 189 166 158 156 145 145 131 71 67 62 58 27 112,875 88,910 35,475 38,700 65,145 43,215 73,530 60,630 118,680 57,405 32,250 41,925 30.960 403,125 308,665 298,345 248,970 212,850 209,625 194,790 179,310 174,150 169,635 167,055 161,895 152,865 147.705 139,320 134,160 131,580 123,195 121,905 107,070 101,910 100,620 93,525 93,525 84,495 45,895 43,215 39,990 38,410 17.415 Ailanthus glandulosa Syringa vulgaris Helianthus annuus Brassica oleracea Platanus occidentalis Populus dilatata Solanum dulcamara Euphorbia cypurissias Maclura aurantinca Betula alba Berberis vulgaris Buxus sempervirens Asclepias incarnata Taxus baccata Zea inais Chenopodium ambrosioides. . Ficus elastica Ribes aureum Populus monilifera Pinus sylvestris , Anemone nemorosa 1 /i 1 in in bulbiferum Iris Germanica A vena sativa. . . *Ia a paper on the Number and Size of Stomata, published in Pringsheim's " Jahrbucher fur Wissenschaftliche Botanik," 1865. THE EPIDERMAL SYSTEM. 10:5 (d) In the plants he examined he found that there were 54 species with from 1 to 100 stomata per sq. mm. 100 to 200 aootoaoo 300 to 400 400 to 500 500 to 600 600 to 700 = 645 to 64.500 per sq. inch = 64,000 to 129,01)0 " = 129,000 to 193,500 " = 193,500 to 258,000 " = 258,000 to 322,500 " " = 387,000 to 451,500 (e) Morren's measurements* vary somewhat from those given by Weiss. The following, not given by Weiss, are taken from Morren's table: In one square millimetre. In one square inch. Upper side. Under side. Upper side.junder side. Trifolium pratense Humulus Lupulus 207 75 49 385 256 253 246 196 155 115 91 86 42 133,515 48,375 31,605 216,075 165,120 163,185 158,670 126,420 99,975 74.175 58,695 55,470 27,090 Vitis vinifera Pirus communis Philadelphus coronarius Secale cereale (/) The stomata of the so-called Compass Plant (SUphium lacinia- tum) are nearly equal in number on the two sides of the vertical leaves ; there are on the true upper surface 82 per sq. mm. (= 52,700 per sq. inch), and on the under surface, 87 per sq. mm. (= 57,300 per sq. inch).f (g) On most leaves the Btomata are not distributed equally over all portions of either surface ; they are not found on the veins, but are restricted to the areas between them. In some plants this restriction is accompanied by a further modification, as in Geanothus prostratus, where the stomata are confined to the bottoms of sunken pits which occur on the under side of the leaves. In the long harsh leaves of Stipa spartea the stnmata of the upper surface are restricted to the sides of the deep longitudinal channels which lie between the promi- nent nerves. (See Figs. 135-6, pa/t, bundles of sieve tissue ; pp. narrow peripheral (and first formed) ves- sels ; g, large and still young vessel. After Sachs. in places it is impossible to tell whether the tissues belong to them or to the surrounding ground tissues. The inner portion of the bundle (g, g, t, t. Fig. 106, and s to #, Fig. 107) is made up of tracheary tissue of several varieties; on the inner edge of this tracheary portion lie several spiral ves- sels (s, s, Fig. 107) ; next to these, on their outer side, are sca- lariform and pitted vessels (/, f, g, g, Fig. 106, I, t, t', Fig. 107), intermingled with elongated cells, whose walls arc pitted 116 BOTANY. (h, h' , h", h'", Fig. 107). The last-named are clearly related to the vessels which surround them, and from which they differ only in their less diameter, and in having imperforate horizontal or oblique septa. They are doubtless properly classed with the Tracheides (see p. 84). On the outer side of the tracheary portion just described lies a mass of narrow, somewhat elongated, thin-walled cells, which constitute a true meristem tissue, to which the name of Cambium* has been given (c, c, Figs. 100 and 107). Next to the cambium Pig. 105. A very thin cross-section of the radial fibre- vaecular bundle of an old adventitious root of Acorns calamus, g, the radial plates of tracheary tissue ; w, the sieve tissue alternating with the plates of tracheary tit-sue ; , the bundle-sheath ; the tissue in the centre of the bundle is sclerenchyma. x 145. After De Bary. lie, in order, sieve tissue and parenchyma; these do not occupy separate zones, but are more or less intermingled, forming a mass sometimes called the Soft Bast (y, y, y, Fig. 106, and p, Fig. 107). The sieve tissue includes sieve tubes and cambiform or latticed cells. In the extreme outer border of the bundle is a mass of fibrous tissue (b, b, Figs. 106 and 107). The layer of starch-bearing cells just outside of the last- named tissue is the so-called bundle sheath. * Cambium, a low Latin word, meaning u liquid which becomes orlutinous. The term wns introduced wh.-n the real structure of the part to which it was applied was not understood. THE FIB RO- VASCULAR SYSTEM. 117 146. The bundle of the adventitious root of Ranunculus repens is very different from the one just described. It may be briefly described as composed of a mass of tracheary tis- Fig. 106. Transverse section of hypocotyledonary portion of stem of Ricinus com- mimis. r, r, parenchyma of the prinnry cortex ; w, parenchyma of the pith . b, bast fibres ; y, y, soft, bast; c, cambium ; g, g, large pitted vessels ; t, t, smaller pit- ted vessels ; cb, continuation of the cambium into the pan-nchjma lying between the bundles the parenchyma-cells are repeatedly divided by tangential walls. Between the primary cortex r and the fibrous tissue of the phloem lies a layer, the so-called bundle-sheath, filled with compound starch grains. Highly magnified. After Sachs. sue, which is cross-shaped, as seen in transverse section (g, r, g, Fig. 108), and four masses of sieve tissue, which lie in the angles between the projecting portions of the traoheary tissue. Around the whole is a layer of pericambium (p, 118 BOTANY. Fig. 108), and exterior to this is the bundle sheath (u, Fig. 108). 147. In Gymnosperms and Dicotyledons the fibro-vascu- lar bundles of the stems have a structure essentially like that of Ricinus communis, described above In them it is evi- dent at a glance that the bundle is divided into two some- what similar portions, an inner and an outer, by the cam- h I, Pig. 107.-Longitndinal radial section of the fit - - it (the transverse section being shown in Fig. cortox ; 0, bundle sheath ; in, parenchyma o bium zone. Xiigeli,* who first pointed out these divisions, named the inner one the Xylem portion, because from it the Avood of the stem is formed ; the outer he named the Phloem portion, for the reason that it develops into bark.f In pome cases the similarity between the structure of xylem * " Beitrage zur Wissenschaftlichnn Botanik," 1858. f Xylem from i ; /oi<, wood ; Phloem from Greek ^ot bark. THE F1BRO-VA8VULAR SYSTEM. 119 and phloem is so marked that they are said to be composed of corresponding tissues. (1) Vascular, (2) Fibrous, and (3) Parenchymatous. * The vascular tissues are, on the one hand, the tracheary tissue found only in the xylem, and on the other, the sieve tissue of the phloem. The fibrous tissue of the xylem is the variety with the shorter and harder Fig. 108. Cross- 8ection of the flbro-vascular bundle of an old adventitious root of nwm nodus repent. i/nminosa; the ., . , . , ends x, x, are cut ..ff in making the more easily after soaking the stems, roots or leaves used in alcohol. preparation, the other* are the actn termini ; the bundles are seen to be composed of spiral tracheldes. and ESS e (c) In many cases it is profitable to macerate some of tlie longitudi- nal sections in nitric acid and potassi- um chlorate (Schulze's maceration), so as to permit of an isolation of the fibres, cells, and vessels. (d) Good specimens for study may be obtained from any of the higher plants, but the examination will be most profitable if the 1 order cells of the chlorophyll-bearing part-n chyma. X 22o.-After De Bary. * For the various contrivances used for cutting sections see the com- mon books on microscopy, also American Naturalist, 1874, p. 59 ; American Quarterly Microscopical Join mil, 1879, p. 131, and several articles in Qr. Jour. Mic. Science, 1870, 1874, 1875, 1877. THE FUNDAMENTAL SYSTEM. 123 in the following list of examples is observed : (1) the rhizomes and roots of ferns ; (2) stems of Selaginella and Lycopodium ; (3) stems of Monocotyledons ; (4) stems of Equisetum ; (5) young stems of Gymno- sperms and Dicotyledons ; (6) roots of Phanerogams ; (7) reduced bundles of leaves. (c) The discussion of the disposition of the bundles in the stem, and their relation to the leaf bundles, together with the development and structure of secondary bundles, belongs properly to the special anatomy of the Phanerogams. (See Chapter XX.) IV. THE FUNDAMENTAL SYSTEM, OR THE SYSTEM OF GROUND TISSUES. 153. These terms refer to the mass of various tissues lying within the epidermis, and not included in the fibro- vascular bundles, when they are present. In passing down through the lower plants this inner mass becomes more and more simple, until it is composed of but one homogeneous tissue, when the term system can no longer be profitably applied to it ; in passing to the higher plants, on the other hand, there is in this portion of their structure an increasing complexity, which comes at last to more than equal that of either the epidermal or fibro- vascular systems. 154. In its fullest development, the fundamental system may contain parenchyma of various forms, collenchyma, sclerenchyma, laticiferous tissue, and possibly also fibrous tissue.* Their arrangement, within certain limits, presents a considerable degree of similarity in nearly related groups of plants, but this is by no means as marked as in the case of the fibro-vascular system. * It is a question whether fibrous tissue occurs in the fundamental system ; there are some cases (e.g., in Ferns, Lycopodiaceae, etc.) which appear to show that it does, but possibly they admit of other in- terpretation. It should be mentioned here that many eminent botanists (notably Schwendener, Russow, Falconberg, and De Bary) hold that all fibrous tissue belongs to the fundamental system, and as a consequence, that it in no case is a proper constituent of the fibro-vascular bundle. This is, however, nothing more than making a typical form of bundle (composed of tracheary and sieve tissues), and then insisting that all tis- sues not found in the type are extra-fascicular, a course which cannot be followed in this book. 124 BOTANY. (1.) Parenchyma is the most constant of the fundamental tissues ; it makes up the whole of the interior plant-body in those cases where there has been no differentiation into more than one tissue, and from here, it is present in varying amount in nearly all (if not all) cases up to and including the highest plants. In stems of Monocotyledons it makes up the mass of tissue lying between the scattered bundles, and in stems of Gymnosperms and Dicotyledons it constitutes the pith and portions of the bark. (2.) Collenchyma, when present, as it frequently is in the stems and leaves of Dicotyle- dons, is always either in con- tact with or near to the epi- dermis. (3.) Sclerenchyma is com- mon beneath the epidermis of the stems and leaves of Bry- ophytes, Pteridophytes, and Phanerogams. It appears to replace collenchyma in parts having greater firmness than that given by the latter. Some forms of sclerenchyma are scarcely to be distinguished from fibrous tissue e.g., in the hypoderma of pine leaves (Fig. 110, y, i'). It may be that the supposed cases of fibrous tissue among the funda- mental tissues will turn out to be sclerenchyma instead. (4.) Laticiferous tissue may occur, apparently, in any por- tion of the fundamental system of Phanerogamous plants. 155. It is thus seen that in general the tissues of the fundamental system are so disposed that the periphery is harder and firmer than the usually soft interior, although there are many exceptions. This general structure has given rise to the term Hypoderma for those portions of the funda- mental system which lie immediately beneath, or near to the epidermis. Hypoderma is not a distinctly limited portion in fact, it is often difficult to say how far it does extend ; Fig. 110. Margin of leaf of Pimti pin- aster, tranevorse section ; c, cnticular- ized layer of outer wall of epidermis ; i, inner non-cuticularized layer ; c', thick- ened outer wall of marginal cell ; g, i', hypoderma of elongated sclereiichyma ; p, chlorophyll-bearing parenchyma ; pr, contracted protoplasmic contents. X 800. After Sachs. THE FUNDAMENTAL SYSTEM. 125 however, it usually includes several, or even many, layers of cells, or the whole of each of the tissue-masses (e.g., colleu- chyma, sclerenchynia, etc.) which immediately underlie the epidermis (Fig. 110, g, i). The remaining portion of the fundamental system, inside of the hypoderma, is designated by Sachs as the Intermediate tissue. The term is of but little value in many of the higher plants, where more particular names may be applied ; but in some Monocotyledons, most Pteridophytes, and in Bryo- phytes it is very serviceable. 156. Cork. Within the zone which the hypo- derma includes there frequently takes place a pe- culiar develop- ment of the young parenchy- ma, giving rise to layers of dead cells, whose cav- ities are filled with air only. The walls in some cases (e.g., tlio r>rT-lr roV\ aro tne COrK-OaKj aie thin and weak, while in others (e.g., the beech) they are much thickened, and in all cases they are nearly impermeable to water. True cork is destitute of intercellular spaces, its cells being of regular shape (generally cuboidal) and fitted closely to each other (Fig. 111). 157. Cork substance is formed by the repeated subdivis- ion of the cells of a meristem layer of the fundamental tissue (Fig. Ill) ; these continue to grow and divide by parti- tions parallel to the epidermis, forming layers of cork with its cells disposed in radial rows (Fig. Ill, k). Shortly after Fig. 111. Transverse section of one-year old stem of Ai- lant/itig glandulosm. e. epidermis ; *, cork-cells ; r, inner green cells, the phelloderma ; between k itnd r a layer of cells tilled with protoplasm, called the phellogen or cork cambium. X 350. After Prantl. 136 BOTANY. their formation the cork-cells lose their protoplasmic con- tents, while beneath them new cells "are constantly being cut off from the cells of the generating layer ; in this way the mass of dead cork tissue is formed and pushed out from its living base. 158. The generating tissue is called the Phellogen,* or Cork-cambium ; it occurs not only in the hypoderma, but in any other part of the fundamental system, and, as will be shown hereafter, in the secondary fibro- vascular bundles. AVhen a living portion of a plant is injured, as by cutting, the uninjured parenchyma-cells beneath the wound often change into a layer of phellogen, from which a protecting mass of cork is then developed. 159. Lenticels are in many cases the result of a restricted corky growth just be- neath a stoma. Phel- logen consisting of a few Cells Of the hypo- Fig. 112 Transverse section of a portion of the , ... ,*T internode of a younj.' twig of R*tnla nlt>a. c, cuticle, derma, IS formed im- somewhat separated from the epidermis ; <>, e, epider- -,. , , , , mis ; a, cavity under ihe htomaeeen in cros^ection mediately DCIOW a abov<; ; a, x, cells whi< h are beginning the process of 4- r . rrlo /T?\rr 11O \ . multiplication by fission. conMftutins ; the phellogen Stoma (big. 112, X) J of the future lenticel. X 875. -After De Bary. by the g rowt h o f COrk from this phellogen the epidermis is pushed out and finally ruptured, exposing the roundish or elongated mass of corkf (Fig. 113). Lenticels are of frequent occurrence on the young branches of birch, beech, cherry, elder, lilac, etc., and may be distinguished by the naked eye as slightly elevated roughish spots, usually of a different color from the epidermis. () The examination of the tissues of the fundamental system may in general be made with considerable ease, by making trans verse, tan- gential and radial sections. * From the Greek ^eJUoc, cork. f It appears quite certain that not all lenticels develop from the hypoderma beneath stomata ; phellogen forms beneath the epider- mis at other points, and gives rise to lenticela in a way essentially as in the other cases. THE FUNDAMENTAL SYSTEM. 127 (b) Ordinary herbaceous Dicotyledons furnish the best examples of fully developed fundamental tissues ; they can be most easily exam- ined after soaking for some time in alcohol. (e) Examples of thin-walled cork are, of course, best obtained from Fig. 113. Transverse section through a lenticel of Betula alba, e, e, epidermis ; , old stoma ; under this i* a mass of cork which develops from the phellogen layer lying next to the ordinary parenchyma (figured darker) ; the great multiplication of cork-cells has pushed out the epidermis. X 280. After De Bary. the ordinary commercial article ; the thick-walled form may be obtained from the bark of the beech, willow, prickly ash (Xanthoxylnm Amer- icanum), Viburnum opulm, etc. Its development may be observed by making successive sections of the shoots at different heights. CHAPTER VIII. INTERCELLULAR SPACES AND SECRETION RES- ERVOIRS. 160. In addition to the cavities and passages which are formed in the plant from cells and their modifications, there are many important ones which are intercellular, and which at no time were composed of cells. In some cases they so closely resemble the cavities derived from cells that it is with the greatest difficulty that their real nature can he made out. In. their simplest form they are the small irregular spaces which appear during the rapid growth of parenchyma-cells (Fig. 51, p. 67) ; from these to the large regular canals which are common in many water plants there are all inter- mediate gradations. 161. In leaves, especially in the parenchyma of the under portion, there are usually many large irregular spaces be- tween the cells ; they are in communication with the exter- nal air through the stomata, and contain only air and watery vapor. The petioles and stems of many aquatic plants con- tain exceedingly large air- conducting intercellular canals, which occupy even more space than the surrounding tissues (Fig. 9, page 20). In the Water-lilies (Nymphceacece) and Water-plantains (Alismacece] they are so large as to be read- ily seen by the naked eye, and in the Naiads (\ni(i. soil hast ; E, fully developed canal, g ; b, bast ; rp, cortical parenchyma, x 800.- Aftur Sachs. odorous substances are collected. The fragrance of many fruits e.g., oranges and lemons is due to the oils and other matters contained in such Receptacles. In Dictamuiis fra.r- inflla these are developed as follows : two mother-cells (p, p, Fig. 116) appear in the hypoderma and divide by several partitions, forming a mass of thin-walled secreting cells (Fig. 116, B) ; these, by a degeneration of their walls, fuse into a common cavity filled with oil and watery matter (Fig. 116, C). It appears that the outer layer of secreting cells (c, c) is developed from the epidermis (Fig. 116, A, d, c); hence this is partly an epidermal structure. Of like nature are the reservoirs in the "glandular hairs " of the same plant ; in fact, the two structures are apparently SECRETION RE8ER VOIRS. 131 but slightly different developments of the same organ (Fig. 117). (a) The smaller and more irregular intercellular spaces may be studied in the fundamental tissue of the stem of Indian corn, in the parenchyma of most leaves, and the stems of Juncm. FIG. 116. Fm. 117. Fig. 116. Internal glands of the leaf of Dictamnw fraxineUa. A and B, curly stages of development; C, mature gland ; d, epidermis ; c, p, mother-cells of the ue- creting cells ; o, drop of ethereal oil. After Rauter. Fig. 117. Glandular hair of the inflorescence of Dictamnus fraxineUa ; A and B, earliest stages, showing the origin to be similar to that of the internal glands ; C, fully developed hair ; the part h is the true hair, while all below it, including the oil cav- ity, is to be regarded as an outgrowth of the sub-epidermal cells. X about 220. After Rauter. (6) Thin cross-sections of the etems and petioles of NymphcKfi, Nuphar, Ndumbium, Sagittaria, Potamogeton, and many other water plants, afford excellent specimens for the study of intercellular canals. 132 BOTANY. The relation of the intercellular spaces of the leaves to the canals of the petioles may be studied by carefully made longitudinal sections. (c) The resin canals of Stttphium laciniatum and S. perfoliatum, and the turpentine canals of Coniferae, furnish excellent examples of the larger secretion reservoirs, while the smaller ones may be studied in the cavities in the rind of the orange and lemon, the leaves of Dictam- mis, Xanthox'ilum, Rue (Ruta), Hypericum, and many Labiatae. CHAPTER IX. THE PLANT-BODY. I. GrENEEALIZED FOKMS. 164. The cells, tissues, and tissue systems described in the preceding pages are variously arranged in the different groups of the vegetable kingdom to form the plant-body. The simplest plants are single cells or undifferentiated masses of cells ; in those next higher the cells are aggre- gated into simple tissues, while still above these the tissues are grouped into tissue systems. With this internal differ- entiation there is a corresponding differentiation of the ex- ternal plant-body. The lower plants are not only simpler as to their internal structure, but they are so as to their exter- nal form as well. The higher plants are as much more complex than the lower ones as to their external parts as they are in regard to their tissues and tissue systems. 165. In the lowest groups of plants the simple plant- body has no members ; the single-or few-celled alga has no parts like root, stem, or leaf ; it is a unit as to its external form. In the higher groups, on the contrary, the plant- body is composed of several to many less or more distinct members. In those plants in which they first appear, the members are not clearly or certainly to be distinguished from the general plant-body ; but in the higher groups they be- come distinctly set off, and are eventually differentiated into a multitude of structural and functional forms. 166. As will be seen in the future chapters, every plant, in its earliest (embryonic) stages, is simple and memberless ; and every member of any of the higher plants is at first indis- tinguishable from the rest of the plant-body ; it is only in 134 BOTANY. the later growth of any member that it becomes distinct ; in other words, every member is a modification of, and develop- ment from, the general plant-body. Likewise, where equiva- lent members have a different particular form or function, it is only in the later stages of growth that the differences appear. All equivalent members are alike in their earlier stages, whether, for example, they eventually become broad green surfaces (foliage leaves), bracts, scales, floral envelopes, or the essential organs of the flower. 167. These facts make it necessary to have some general terms for the parts of the plant-body, which are applicable to them in all their forms. We must have, for example, a term so generalized as to include foliage leaves, bracts, scales, floral envelopes, and all the other forms of the so-called leaf- series. So, too, there is need of a term to include stems, bulbs, bud, and flower axes, root-stocks, corms, tubers, and the other forms of the so-called stem-series. 168. By a careful study of the members of the more perfect plants we find that they may be reduced to four general forms, viz., (1) Caulome, which includes the stem and the many other members which are found to be its equivalent ; (2) Phyllome, including the leaf and its equiva- lents ; (3) Trichome, which includes all outgrowths or ap- pendages of the surface of the plant, as hairs, bristles, root- hairs, etc. ; (4) the Root, which includes, besides ordinary subterranean roots, those of epiphytes, parasites, etc. 169. As indicated above, in the lower plants the differ- entiation into members is not so marked as in the higher, and in passing downward in the vegetable kingdom groups are reached in which it is inappreciable, and finally in which it is entirely wanting ; such an undifferentiated plant-body is called a Thallome, and may properly be regarded as the original form, or prototype. 17O. Thallome.* The simplest thallome is the single 'cell ; this, though generally rounded, is, in some cases (Botrydium, Caulerpa, etc.), irregularly extended into branch-like or leaf-like portions, which must not be mistaken * From the Greek t?a//i)9, a young shoot, branch, or frond. GENERALIZED FORMS. 135 for members coordinate with those mentioned above, as they are only parts of a unit, instead of members of a body ; they may be regarded as, to a certain extent, foreshadowings or anticipations of the members of the higher plants. Plants composed of rows of cells or cell surfaces frequently show no indication whatever of a division into members ; but, in some cases, there is a little differentiation, which, though [not carried far enough to give rise to members, is the same in kind. In the larger algae there is sometimes so much of a differentiation that it becomes difficult to say why certain parts ought not to be called members. Caulome and phyl- lome, at least, are strongly hinted at in the Fucaceae, and in this group, although the term thallome is applied to the plant-body, it must be admitted as not fully applicable. Structures of this kind are instructive, as showing that the passage from the thallome plant-body to that in which members are differentiated is by no means an abrupt or sudden one. 171. Mutual Relations of Thallome, Caulome, and Phyllome. The caulome is the phyllome-bearing axis of the plant, and phyllomes are the members developed upon the caulome. The two have a reciprocal relation, and in no case is the one present without the other. The definition of the one involves that of the other. Both are derived directly from the thallome, and that differentiation which gives rise to one necessarily produces the other. The differ- entiation of thallome into caulome and phyllome is simply a lobing and contraction of the marginal portions into sepa- rable phyllomes, and a rounding and contraction of the central or axial portion into a caulome. 172. Caulome.* By this general name we designate all axial members of the plant. In the more obvious cases the caulome is the axis which bears leaves (foliage), and in this form it constitutes (1) the Stem; branches are only stems which originate laterally upon other stems. The other caulome forms are : (2.) Runners, which are bract-bearing, slender, weak, and trailing. * From the Greek xniv.oS, stem. 136 BOTANY. (3.) Root-stocks, which are bract or scale-bearing, usually weak, and subterranean. (4.) Tubers, which are bract or tcale-bearing, short and thickened, and subterranean. (5.) Corms, which are leaf -bearing, short and thickened, and subterranean. (6.) Bulb-axes, which are leaf-bearing, short and conical, and subterranean. (7.) Flower-axes, which are bract, perianth, stamen, and pistil-bearing, short, and usually conical and aerial. (8.) Tendrils, which are degraded, slender, aerial cau- lomes, nearly destitute of phyllomes. (9.) Thorns, which are degraded, thick, conical, aerial caulomes, nearly destitute of phyllomes. 173. Phyllome.* The phyllome is always a lateral member upon a caulome. It is usually a flat expansion and extension of some of the tissues of the caulome. Its most common form is (1) the Leaf (foliage), which is usually large, broad, and mainly made up of chlorophyll-bearing paren- chyma. The other phyllome forms are : (2.) Bracts, which are smaller than leaves, generally green. (3.) Scales, which are usually smaller than leaves, wanting in chlorophyll-bearing parenchyma, and with generally a firm texture. (4.) Floral envelopes, which are variously modified, but generally wanting in chlorophyll-bearing parenchyma, and with generally a more delicate texture. (5.) Stamens, in which a portion of the parenchyma de- velops male reproductive cells (pollen). (6.) Carpels, bearing or enclosing female reproductive organs (ovules). (7.) Tendrils and Spines, which are reduced or degraded forms, composed of the modified fibro-vascular bundles, and a very little parenchyma ; in the first the structures are weak and pliable, in the latter stout and rigid. The altogether special modifications of the phyllome, as in pitchers and cups, will be noticed hereafter. * From the Greek fvMav, leaf. GENERALIZED FORMS. 13? 174. Trichome.* The trichome is a surface appendage consisting of one or more cells usually arranged in a row or a column, sometimes in a mass. Its most common forms are met with in (1) the Hairs of many plants. (See page 95.) The other trichome forms are : (2.) Bristles, each consisting of a single pointed cell or a row of cells, whose walls are much thickened and hardened. (3.) Prickles, like the last, but stouter, and usually com- posed of a mass of cells below. (4.) Scales, in which the terminal cell gives rise by fission to a flat scale, which soon becomes dry. (5.) Glands, which are generally short, bearing one or more secreting cells. (6.) Root-hairs, which are long, thin, single-celled (in mosses a row of cells), and subterranean. (7.) Sporangia of Pteridophytes, some of whose interior cells develop into reproductive cells (spores). (8.) Ovules of Phanerogams, one or more of whose cells develop into reproductive cells (embryo sacs).f 175. Root. The root is that portion of the plant-body which is clothed at its growing point with a root-cap. In ascending through the vegetable kingdom roots are the latest of the generalized forms to make their appearance, and in the embryo they appear to be formed later than caulome and phyllome. They present fewer variations than any of the other generalized forms. The ordinary (1) Sub- terranean roots of plants are typical. They differ but little from one another in all the groups of the Pteridophytes and Phanerogams. The other root forms are : (2.) Aerial roots, Avhich project into the air, and often have their epidermis peculiarly thickened, as in the epiphytic orchids. (3.) Roots of Parasites, which are usually quite short, and * From the Greek tfp/'f, rpn;6s, a hair. f It is held by some botanists that in some plants the ovule is "the terminal portion of the axis," and that in others it is a leaf or part of a leaf. 138 BOTANY. in some cases provided with sucker-like organs, by means of which they come into a more intimate relation to their hosts. 176. Particular Relations of Phyllome to Caulome. Sachs* has formulated the relations of phyllome to caulome in substance as follows : (1. ) Phyllomes always originate from the Primary Meris- tem of the punctum vegetationis ; fully differentiated tissues are incapable of producing them. (2.) They are always exogenous formations ; that is, they FIG. 119. FIG. 118. Fig. 118. Diagrams of dichotomous branching. A, normal dichotomy, in which ch branch is again dichotomonaly branched ; B, helicoid dichotomy, i right-hand branch, r, does not develop further, while the left-hand one, I, is in every case again branched ; C, scorpioicl dichotomy, in which the branc further developed. After Sacns. Fig. 119. Diagram of botryose monopodial branching. The numerals indicate the 'generations.'' develop from outer and not inner tissues, consequently their tissues are externally continuous with those of the caulome. (3.) They always originate below the growing apex of the caulome as lateral outgrowths ; they may appear singly, so that no two are situated at the same height on the stem, or two or more may grow at once, generally at equal distances from one another in the circumference of the caulome. *" Text-Book," p. 181. GENERALIZED FORMS. 139 (4.) They always arise in acropetal* order. (5.) They grow more rapidly than the caulome does above their insertion. When they are numerous their rapid growth gives rise to the accumulation of phyllomes known as a Bud. (6.) The phyllomes of any plant are always of a different form than the caulomes. 177. General Modes of Branching of Members. There are two general modes of the branching of the members of the plant-body. In the one, the apex of the growing mem- ber divides into two new growing points, from which branches proceed ; this is the Dichotomous mode of branching (Fig. \ Pig. 120. Diagrams of cymose monopodial branching. A and B, scor. C, forked cymose monopodium. the compound or falsely dichotomous cyme I also the dicnasium) D, helicoid cyme. After Sachs. 118). In the other, the new growing points arise as lateral members, while the original apex of the parent stem still retains its place and often its growth ; this is the Mono- podial mode of branching (Fig. 119). Both modes are sub- ject to many modifications, the most important of which are briefly indicated in the following table : A. DICHOTOMOUS. 1. Forked dichotomy, in which both branches of each bifurcation are equally developed (Fig. 118, A). * Acropetal, tending toward the summit; fr>in the Greei *,>a. summit, and nerda, to move toward. 140 EOT ANT. 2. ttympodM dichotomy, in which one of the branches of each bifur- cation develops more than the other. a Helicoid *ympodial dichotomy, in which the greater development is always on one side (Fig. 118, B). b. Scorpioid sympodiul dichotomy, in which the greater develop- ment is alternately on one side and the other (Fig. 118, G). B. MONOPODIAL. 1. Botryose monopodium, in which, as a rule, the axis continues to grow, and retains its ascendency over its lateral branches (Fig. 1 19). 2. Cymose monopodium, in which the axis soon ceases to grow, and is overtopped by one or more of its lateral brandies. a. Forked cymose monopodium, in which the lateral branches are all developed (Fig. 120, G). b. Sympodial cymose monopodium, in which some of the lateral branches are suppressed ; this may be 6'. Helicoid, when the suppression is all on one side (Fig. 120, D); or b". Scorpioid, when the suppression is alternately on one side and the other (Fig. 120, A and B). Dichotomous branching takes place in many Thallophytes ; it is beautifully seen in the appendages to the perithecia of many Erysipha- cese (e.g., lilac-blight, cherry- blight, etc.) It occurs also in the roots, stems, and leaves of many Pteridophytes, and the leaves and other phyllome structures of some Phanerogams. Monopodial branching is, on the other band, the general rule for all members of the plant-body in Phanerogams, and in Pteridophytes, Bryopbyte&, and Thallophytes very much of the branching is also of this kind.* II. STEMS. 178. The primary stem of a plant first develops from the meristem tissue of the embryo ; its subsequent growth is a growth from the meristem of the punctum vegetationis, to- gether with an intercalary growth of its newer parts. On account of the more rapid growth of its young leaves, it usu- ally happens that the stem is terminated by, and appears to grow from, a bud ; m fact, it is a common statement that stems grow from buds. It will be necessary to examine the bud in detail. * A full discussion of this subject would occupy more space than can be allotted to it in this book, and any attempt to cover the subject in a 1'ew pages would tend rather to confuse the student than to enlighten him. For a good account, the student is referred to Sachs' " Text-Book of Botany," p. 155 ; Hofmeister's " Allgerneiiie Morphologic der Ge- STEMS. 141 179. Tliepunctum vegetationis (growing point) of a stem is generally a conical point ; upon its curved surface a little below its apex the rudiments of leaves appear as slight swell- ings or papillae ; as the growing point elongates, and the rudimentary leaves grow, new ones appear above the pre- viously formed ones. By the more rapid growth of the leaves than the newer part of the stem, the latter comes to be covered with many closely approximated young leaves. This is the usual condition of the ends of growing stems in summer, hence such an aggre- gation of rudimentary leaves may be termed a summer bud. While in the apex of the bud the leaves grow more rapidly than the stem, in its base the growth of the stem is much the most rapid. This later stem-growth is an inter- calary one, and it results in separating the previously ap- proximated leaves a consid- erable distance from one another, forming the inter- nodes of the stem. 180. Winter buds have essentially the same struc- ture, and the same mode of formation. In these, how- ever, most of the phyllome rudiments develop into more or less hardened scales, which grow rapidly and overtop the punctum vegetationis. The basal growth of the bud ceases, and soon its apical growth also, and thus the scaly phyllomes are left in close approxi- mation (Fig. 121). Such a bud is but a state of the ter- minal portion of the leaf-bearing stem, and not a new for- mation or member ; it cannot even be called an organ. 181, Upon the return of warm weather in the spring Fig. 121. Extremity of a branch of the Horse-chestnut (JEsculvii hippocastanitm); a large terminal bud with two smaller lat- eral buds ; a, a, a, scars of fallen leaves. Natural size. After Diichartre. wachse," p. 432, and Eichler's " Bliithendiagramme," page 33 et seq. In each there are many references given to the literature of the subject. 142 BOTANY. the basal growth of the bud is resumed, and shortly after- ward, or simultaneously, the apical growth also. The thick scales separate by the slight elongation of the stem, and being of no further use to the plant they soon fall off. The inter- calary growth of the scale-bearing portion of the stem is gen- erally much less than of that which bears leaves, hence the first internodes which appear in the spring of the year are quite short. The punctum vegetatiouis of such a winter bud, after resuming its activity, goes on developing leaves as lateral members exactly as if there had been no interruption in its activity. Upon the approach of autumn again the Fig. 122. Longitudinal section of the apex of the stem of a moss (Fontinalis anti- pyretica). , apical cell ; a, outer part of one of the segments cut off from apical cell ; , apical cell of a lateral leaf-h.-arin? shoot arising below a leaf; c, firet cell or a leaf ; b, b, cells forming cortex -After Leitgeb. same process of bud-formation takes place by the decrease in the rapidity of extension, and its final cessation ; this is fol- lowed again by the resumption of growth upon the advent of spring. Thus the stem exhibits a periodicity in its growth, and one of its phases is the so-called winter bud. 182. Branches of stems (lateral stems) normally originate in the pnnctum vegetationis as lateral outgrowths (Fig. 122, z) ; each develops first into a conical mass, which then becomes the punctum vegetationis of a new stem, and upon it lateral members arise, as in the case of the principal stem. The new stem may elongate at once into a leafy shoot, as STEMS. 143 takes place in annuals ; on the other hand, it may make but little growth in extension, so forming a bud, as is common in perennials (Fig. 123). Buds like the last, which are apparently sessile upon the parent axis, are said to be lateral, although, strictly speaking, they are terminal upon very short stems. 183. It most frequently hap- pens that new stems arise near to certain leaves. The origin of the stem may be below the leaf, as in many Bryophytes (z, Fig. 122) ; or beside it, as in Equisetacese ; or above it in its axil, as in Monocoty- ledons and Dicotyledons (Fig. 121), and it appears that in each case the new stern originates shortly after the leaf. 184. In Monocotyledons and Dicotyledons there are usually as many new stems formed as there are leaves ; exceptionally there may be several new stems (supernumer- ary stems or buds) formed in the axil of .each leaf (Fig. 123.) In mosses, ferns, and Conifers, on the contrary, there are by no means as many new stems as there are leaves. 185. Rarely, new stems (adven- titious stems or buds) arise from the older parts of plants ; thus they may arise from petioles and ribs of some leaves e.g., Begonia, Bryo- pli i/llum, etc. ; from the cambium of the cut surfaces of stems -e.g., elm, willow, etc.; and sometimes in abundance from the fibrO-VaSClllar bundles of roots e.g., Populus alba, cherry, sweet potato, etc. Such structures are always endogenous, as in all cases they spring from some portion of, or near to, the fibro-vas- cular bundles, and break through the overlying tissues. ural size. After Duchartre. 144 SO TAN T. 186. Frequently the new stems which are normally formed make but a very little growth, and in perennials become covered by the subsequently formed tissues ; they thus become the so-called dormant buds. Under favorable conditions they may resume their growth long afterward, and they are then liable to be mistaken for adventitious stems. Probably very many of the supposed cases of adventitious stems upon the older stems of Dicotyledons are in reality only the late growths of stems which have been dormant for a long time. (si) The development of stems may be studied in almost any plant. Those which have large winter buds, however, offer some advantages to the beginner. Such are the buds of hickory, horse-chestnut, lilac, etc. (6) Vertical sections should be made of the buds before they resume their growth in the spring, and these should be compared with similar sections made after some growth has taken place. (c) Many of the common annuals with a continued growth e.g., balsam, mallow, etc. may be profitably studied for making out the growth of summer buds. The young shoots of many shrubs e.g. , elder and lilac are also excellent for study. (d) Thin enough longitudinal sections should be made to show the punctum vegetationis. The specimens may often be made much more instructive by coloring with carmine, or other staining fluids. III. OF LEAVES IN GENERAL. 187. Every leaf originates in the Primary Meristem of the punctum vegetationis. It is at first a small projection or papilla, composed of one or more cells, which undergo a rapid division, thereby producing the quick early growth before mentioned (p. 139). Generally the multiplication of the cells is such as to give rise to a surface whose plane cuts the stem transversely. In many cases the apex of the leaf soon becomes changed into permanent tissue while the base con- tinues to grow, indefinitely in grasses and many other Monocotyledons, and definitely in most Dicotyledons. In other cases the base passes over into permanent tissue, while the apical portions keep on growing, as in ferns and some pinnate leaves of Dicotyledons. 188. Many leaves are raised upon a stalk by a subsequent growth between the stem and the base of the leaf ; this leaf- OF LEAVES IN GENERAL. U5 stalk (petiole) is much extended in the lower leaves Of many plants, especially of those which grow in the shade or are intermixed with other plants. Structurally the petiole is the extension of the fibre-vascular and parenchymatous connec- tion between the leaf and the stem ; and it generally forms an articulation or joint with the stem at its lower extremity ; physiologically it is a support for the leaf, and it is longer or shorter just as elongation or want of it places the leaf under the best physiological conditions. 189. The leaf is, when first formed, destitute of fibro-vas- cular bundles, and this is the permanent condition of the leaves of Bryophytes, and the leaf -like portions of the Thallophytes. In most higher plants, however, portions of the leaf tissue early become differentiated into one or more fibro- vascular bundles, which pass downward into the stem and unite with the older bundles ; the upper parts of the bundles grow with the leaf, and form lateral branches and branchlets, giving rise to the complicated system of so-called veins so often to be seen (especially in Dicotyledons). In many of the smaller phyllome structures, as scales, bracts, etc., which may be regarded as rudimentary leave *, there are no fibro- vascular bundles, just as in the rudiments of actual leaves. 190. Venation. In mosses and other plants destitute of fibre-vascular bundles, the veins, when present, are composed of but slightly modified parenchyma ; in higher plants they are composed of fibro-vascular bundles and, in the larger veins, of one or more surrounding layers of modified paren- chyma in addition. The disposition of the veins in a leaf depends largely upon its mode of growth. Usually several veins form early ; if they grow from a common point, an arrangement like that in the maple (radiate venation) is the result ; if the veins grow from points on an axis, the various modifications of the pinnate venation are produced, depend- ing upon the amount of elongation of the axis. In many Monocotyledons the leaves continue to gi*ow at their bases ; their veins are, as a consequence, parallel with the leaf axis ; in other Monocotyledons and most Dicoty- ledona the veins originate on an extending axis, and pass outward to or near to the margins. 146 BOTANY. 101. Leaves are for the most part bilaterally symmetrical, a vertical plane passing from base to apex generally dividing them into two equal and corresponding halves. In the elm, linden, begonia, etc., and the leaflets of many compound leaves, the two halves are unequal. The asymmetry is ap- parently related in some way to the position of the leaves on the stem, as it is more frequently noticed on plants whose leaves are two-ranked, with the leaf planes parallel, or nearly so, to the axis of the stem (or in compound leaves, to the central leaf axis). In some two-ranked leaves the upper half of each leaf (i.e., that nearer to the apex of the stem) is the larger, while in others the opposite is the case.* 192. In form leaves are very variable ; even in the same plant it rarely happens that all have the same form. In general, elongated forms (i.e., linear and oblong) prevail in the Monocoty- ledons, while as a rule they are considerably broadened (i.e., lanceolate, elliptical, cordate, etc.) in mosses, ferns, and Di- cotyledons ; many exceptions, however, occur. 193. The absolute size of leaves varies greatly also. The largest leaves as, for example, those of palms, tree-ferns, ba- nana, Victoria regia, etc. occur in the warmer portions of the earth ; in frigid regions the leaves are small ; in tem- perate climates perennial leaves are, as a rule, smaller than annual ones. * See an article on this subject by Professor Beal in American Natu-nli8t, 1871, p. 571, and a still earlier one by Dr. Wilder. Both writers show that in many cases the upper half of the leaf is the most devel9ped, in opposition to De Candolle, who makes the statement that " the side most developed is always the lower." Herbert Spencer's supposition that the want of symmetry is (in some cases) due to the shading of the smaller half of the leaf, they show not to be correct, as the asymmetry is observable in the voung leaves in the unexpanded budl Fig. 124. A, leaf with serrate mar- gin ; S, leaf with dentate or toothed margin ; 0, leaf with crenate or scal- loped margin OF LEA VE8 IN GENERAL. 147 194. Leaves, like other members of the plant-body, may branch during their growth. At first they are always simple, and if the growth is uniform the result is a simple leaf ; if, however, as frequently happens, the growth is more rapid at certain points, branches may arise, as in the so-called com- pound leaves. All grada- tions are observable between simple leaves, in which the growth has been absolutely uniform (producing entire margins), to compound . leaves with jointed leaflets. ( The differentiation is here much like that which takes place in passing from the Fig ' ^--Three-lobed leaf of Hepatica. thallome to the form of plant-body with distinct caulome and phyllome. The simplest cases are those in which the branches are rudimentary, as in the serrate (Fig. 124, A), dentate (Fig. 124, B), crenate (Fig. .124, C], and other similar forms. When the branches are more prominent they give rise to lobes of various kinds (Figs. 125, 126). Where the longitu- dinal growth of the leaf (not of its brandies) is but little, the lobes ap- pear to radiate from a common point, as in hepatica, mallow, maple, etc. ; such are called radiately, pal- mately, or digitately lobed. Where, as in the oak, the longitudinal growth of the leaf is considerable, the lobes are laterally arranged upon * central portion ; such leaves are said to be pinnately lobed. 195. Leaf-brunches frequently become so developed that they themselves form distinct leaves, and thus we have what is termed the compound leaf (Figs. 127 and 128). Terms similar to those used in the case of lobed leaves are here used also ; thus where the secondary leaves (leaflets) grow from an extremely short axis, so that they radiate from a 148 BOTANY. common point, the leaf is said to be radiately, palmately, or digitately compound (Fig. 127, A and ). In those cases where the leaflets grow from an axis which lengthens more Fig. 127. .4, pall compound leaf. lately compound leaf of Horse-chestnut; 2?, palmately trifoliate or less, the leaf is termed a pinnately compound one (Fig. 128, A and B}. It not infrequently happens that in the growth of leaflets they also produce branches, giving rise thus to doubly compound leaves. Fig. Is28 A, pinnately compound leaf ; B, pinnately compound leaf, with common midrib prolonged and metamorphosed into a tendril. (See page 136.) 196. The stipules which occur as lateral appendages upon the petioles of many leaves of Dicotyledons are early leaf- branches which were not carried up by the subsequent eloii- THE ARRANGEMENT OF LEAVES. 149 gation of the petiole ; as in the pea, vetch, agrimony, quince, etc. IV. TUE ARRANGEMENT OF LEAVES (PHYLLOTAXIS). 197. Leaves are disposed on stems in various ways : (1.) They may be in whorls of three or more encircling the stem at intervals. In this case each whorl was formed as a ring of rudimentary leaves about the punctum vegetationis.* The leaves of each succeeding whorl usually appear just above and between the preceding ones, so that the whorls alternate with one another. (2.) Where two leaves originate on exactly opposite sides of, and at the same height on, the punctum vegetationis, the opposite arrangement is produced. Here, as in whorled leaves, the new ones usually arise in the intervals between the previously formed ones, so that the pairs of leaves decus- sate. (3.) If the leaves originate singly (scattered or alternate leaves), the simplest case is that in which each succeeding leaf appears a little above the preceding and on the opposite side of the punctum vegetationis. In this case, where the stems elongate, the leaves are arranged in two opposite lon- gitudinal rows or ranks (orthostichies},\ hence this is called a two-ranked arrangement. (4.) If, instead of each new leaf forming at a point half of the circumference of the punctum vegetationis from the last, it appears at a point distant (always in the same direc- tion) one third of the circumference, there will be three ver- tical rows of leaves upon the stem ; this is the three-ranked arrangement. (5.) In rare cases the succeeding leaf is in each case distant one fourth of the circumference from the last, always meas- uring in the same direction ; this gives rise to the four- ranked arrangement. * There are some cases of false whorls, in which the leaves are first formed at different heights, and only later by irregularities in the growth of the stem become whorled. f From the Greek opi?6s, straight, and orfto?, a row. 150 BOTANY. (6.) It is very common for the young leaves to appear in succession on the punctum vegetationis at a distance equal to two fifths of the circumference from each, producing a five-ranked arrangement. (7.) A seven-ranked arrangement is rarely seen; it is pro- duced by the leaves following each other at a distance of two sevenths of the circumference. (8.) An eight-ranked arrangement, which is a very common one, results from the leaves appearing at the constant distance of three eighths of the circumference. (9.) In like manner there may be formed 9, 11, 13, 14, 18, 21, 23, 29, 34, 37, 47, 55, and 144 ranks. 198. The distance between any two succeeding leaves is called the angular divergence; it may generally (but not always) be deduced directly from the number of ranks (orthostichies); thus in the 2-ranked leaves it is \ ; in the 3-ranked, ; in 4- ranked, \ ; in 5-ranked, f (rarely -J-) ; in 7-rauked, f ; in 8- ranked, f (rarely ); in 9-ranked, f ; in 11-ranked, -fr ; in 13-ranked, -^ ; in 14-ranked, ^ ; in 18-ranked, ^ ; in 21- ranked, 2 R T ; in 23-ranked, -fa ; in 29-ranked, ^ ; in 34- ranked, |f ; in 37-ranked, 7 \ ; in 47-ranked, ffi j i n 55- ranked, f- ; in 144-ranked, -f/ f . Examples of the more common of these arrangements are to be found as follows .* (a.) 2-ranked in Fagus, Cdtis, Ulmux, Vitis, Tilia, most Viciea, and all grasses. (b.) 3-ranked in Carex, Scirpus, and most Jungermannia. (c). 4-ranked in the bracts of tlie principal axis of inflorescence of Restio erectus and Thamnochortus scariosus. (d.) 5-ranked in Quercus, Populus, Robinin, most Rosacece, Borra- ginacfOP, etc. ; this is the most common arrangement in Dicotyledons. (e.) 7-ranked in Melaleuca ericcefolia, EupJiorbia heptagona, Sedum sexangulare, etc. (/.) 8-ranked in Polytrichum, Parietaria erecta, Antirrhinum ma- jus, Raphanus, Brass'ca, Hieracinm piloseUa, etc. (g.) 9-ranked in Lycopodium selago. (h.) 11-ranked not rarely in Sedum reflexum and Opunt (k.) 13-ranked in Verbascum, Rhu* typhina, Twga canadensis. * This list of examples is from Hofmeister's " Allgemeine Morphol- ogic der Qewachse," p. 448 et seq. ARRANGEMENT OF LEA VES. 151 IV (I.) 21-ranked in the weak branches of Abies pectinata and Picea excelsa, and in most cones of these species. (m.) 34-ranked on strong branches of Abies pectinata and Picea excelsa, cones of Pinus larico, and the interfloral bracts of the inflorescence of Jttidbeckia. (n.) 55-ranked in tlie uppermost shoots of many piues and firs, in many Mdinillaricv, etc. (o.) 144-ranked in the interfloral bracts of strong-grown flower-heads of HeMu-nthus annuus. 199. By an examination of various leaf-arrangements, the following interest- ing but not very important facts may be noted (Fig. 129) : (1.) If we draw a line from the inser- tion of one leaf to the one next above and nearest to it, and continue this around the stem to the next, and so on, a spiral will be obtained agreeing with the order of development of the young leaves on the punctum vegetationis. To this line, so drawn, the name of Generating Spiral has been given. (2.) In most cases the spiral passes more than once around the stem before inter- secting leaves of all the ranks. (3.) The number of turns of the spiral about the stem in intersecting leaves of all the ranks equals the numerator of the fraction which indicates the angular di- mem. vergence of the leaves from each other. and bottom in Roman (4.) Two sets of secondary spirals (Par- astichies}* crossing each other at an acute angle may be observed on the stem when the leaves are close together, as in Fig. rranti. 129 ; the leaves numbered 1, 6, 11, and 16 form one of the * It is of great importance that the student should not regard these spirals (generating spirals and parastichies) as anything more than convenient means for describing any particular leaf-arrangement. En- tirely too much attention has been given to working out all kinds of curi- ous mathematical laws, which are, to say the least, absolutely worthless 152 BOTANY. parastichies passing to the right, while leaves 3, 6, 9, 12. 15, 18 belong to the parastichies which pass to the left. (5.) Upon counting, in Fig. 129, it is found that there are three parastichies passing to the left and five to the right ; the smaller number is the same ad the numerator of the fraction expressing the angular divergence, while the sum of the two equals the denomi- nator ; similar rela- tions mav be shown to 130. Diagram of eight-ranked arrange- . , . " , raent; viewed from above. The orthostichieo. which 8X181 111 Other CaSCS. ! appear to be radial lines, are numbered, as in Fig. 129, from /. to VIII The leaves are number- ed from 1 to 16.- After Sachs. 200. If now we study the several ar- rangements by projecting the stem upon a flat surface in such a way that the successive nodes, in ascending the stem, are represented by smaller and smaller concentric circles (Fig. 130) (as would, in fact, be the case if we made sections through the nodes of the punctum vegetationis), it is at once evident that each leaf is so placed as to stand over the vacant space between the previously formed ones, and that as regards the leaves formed after it, it is equally well situated. Hofmeister formulates this Fig. 130a. Cross-section of a leaf-bnd of the Hemlock Spruce (Tntga Canadeit- Sis). Magnified. -After Hofmeister. to the morphologist. So much has this been done, that the study of Phyllotaxis has in some quarters become little more than a species of mathematical gym nasties, ARRANGEMENT OF LEAVES. 153 as follows :* "New lateral members have their origin above the centre of the widest gaps which are left at the cir- cumference of the punctum vegetationis between the in- sertions of the nearest older members of the same kind ;" and no doubt this is one of the most important immediate causes which determine where each new leaf is to arise. If it be asked why, then, are not all leaves arranged alike, the answer must be looked for in the differences in structure of the puncta vegetationes. In cases where there is an apical cell, the arrangement of the leaves may be directly traced to its mode of division. In Phanerogams it is often clearly due Fig. 1306. Cross-section of the leaf-bud of the chestnut (Castaneavesca). >,*, the scale-like leaves;/" 1 ,/ 2 ,./ 13 , etc., the rudimentary leave*; s'-s 1 . s a -* 2 , etc., the stipules belonging to the correspoiulini'ly numbered leaves. Magnified. After Hofmeitter. to a difference in the size and form of the punctum vegeta- tionis ; in Conifers and Composites, for example, it is com- mon for a change in the arrangement to take place in pass- ing from the foliage leaves to the bracts of the inflorescence upon the same stem, the number of ranks in such cases being greater on the larger axes. Doubtless some of the dif- ferences can be explained only by taking into account, also, the inherited peculiarities of the plant. * " Allgem. Morphol.," p. 482, and quoted in Sachs' il Text Book," p. 177. 154 BOTANY A study of actual cross-sections of leaf-buds will make the truth of the previous statements more clearly evident. Hof- Pig. 130e. Cross-section of a lateral bnd of the Virginia Creeper (Ami>elop#ia quin- quefolia)) showing arrangement of parts in a double bud. Magnified. After Hof- meister's figures,* several of which are here reproduced (Figs. 130, , to 130, d), show that in all cases the leaf rudiments occupy in the bud the positions in which they meet with the least resistance. This is beautifully shown in the leaf-bud of the Hemlock Spruce (Fig. 130, a). In the leaf-bud of the chest- nut (Fig. 130, J), the large stipules form the F g. Iftod. Crofs-gection of the leaf-bud of a youni: plant of Indian corn (Zta mais\. /., the bud-SCales : but here, US cotyledon, with its two fibro- vascular bundles, 1, 1'; . ' II, III.. IV., V., the successive leaves, their mid- m the preceding Case, ribs marked by a dot. Magnified.-After Hofmeis- L*TI ter. growth appears to follow the "lines of least resistance," the young leaves occupying the interspaces between the stipules. The double lateral bud * In " Allgein. Morphol." INTERNAL STRUCTURE OF LEAVES. 155 of the Virginia Creeper (Fig. 130, c) may also be studied with profit, and it is curious to see how the positions of some of the leaves are altered by the fact that the bud is a double one. The bud of the Indian corn (Fig. 130, d) shows that the same law holds in the Monocotyledons as in the Dicotyledons. V. THE INTERNAL STRUCTURE OF LEAVES. 201. The internal structure of leaves varies considerably. In all cases, however, the leaf is composed mainly of thin- walled, chlorophyll-bearing parenchyma, and this is to be re- garded as the proper leaf tissue. The fibro-vascular bundles constitute little more than the framework of the leaf and its connection with the stem, while the epider- mis is here, as elsewhere in the plant, a covering tissue. In the related members of the plant, such as bracts, scales, floral envelopes, and other phyllome struc- tures, chlorophyll-bear- ing parenchyma is gen- erally wanting, but from true leaves it is rarplvpvpr nb^fMit Tlip rarely ever absent, i ic Shape Of the leaf, its parenchyma constituting the "palisad * ... _ X, the loo*e and irregular parenchyma of the lower Size, position, and re- part of the leaf. In a part of the section the chlo- , ,. ,, rophyll granules are shown. x 250. From a UltlOn tO 'Other mem- drawing by J. C. Asthur. bers, all have somewhat to do with securing the best disposi- tion of the essential leaf tissue. 202. In leaves composed of one layer of cells, as in many mosses and some ferns, obviously there is no need of any special arrangement of the cells in order to secure their best exposure to light, heat, gases, etc. In thick leaves, however, the internal cells are clearly not so well situated as the external ones are, hence we find such leaves possessing some peculiarities in their structure which obviate this difficulty. Instead of being composed of solid tissues, their cells are 156 BOTANY. Fig. 132.-Section of tne " pali- ***' tissue of the leaf of />- sade generally loosely arranged, with large intercellular spaces be- tween them (Figs. 131 and 133), and these are in free com- munication with the external air by means of the stomata. It most frequently happens that this loose tissue is in the under part of the leaf, while the upper portion is composed of one or more layers of closely placed cells ; and this agrees with the general distribution of the stomata, there being usually many more on the under than the upper surface. 203. The upper denser tissue, termed palisade tissue, is composed of elongated cells, which stand at right angles to the surface of the leaf (Fig. 131). In cross-section the palisade-cells are cylindrical, with small intercellular spaces between rom a drawing by J. C. Arthur. tl iem ^pig. 132), 01' in SOHIG CaSCS they are more or less compressed and angular. In general, palisade tissue is confined to the upper surface of the leaf, the lower being occu- pied by the loose tissue previously mentioned ; but there are some cu- rious exceptions to this rule. The most notable of these is found in the leaf of Silphium laciniatum the so-called Compass Plant* of the Mississippi Valley ; its chloro- phyll-bearing parenchyma is almost entirely arranged as palisade tissue, so that the upper and lower por- tions are almost exactly identical in structure (Fig. 134). The ver- phy]] granuleg tical leaves of the Manzanita of drawing by j. c. Arthur, the Pacific Coast (Arctostaphylos pnngens, var. platypJiylla] have a similar structure. * For descriptions of this curious plant, whose leaves have a marked tendency to eland with one edge to the north and the other to the INTERNAL STRUCTURE OF LEAVES. 204. Another curious leaf structure is to be seen in Stipa spartea, the Porcupine Grass of the interior ; each long harsh leaf is longi- tudinally channel- led on its upper surface, which, by the twisting of the basal portion of the leaf, becomes apparently the low- er, and the chlo- rophyll-bearing pa- renchyma is con- fined to the sides of the channels (Figs. 135 and 136). At the bottom of each channel the epider- mal cells are pe- culiarly developed into a hygroscopic tissue, which, by contracting, closes the channels and rolls the leaf to- gether, as always takes place in dry (a) Many Monocoty- ledons as, for exam- ple, Iris and Indian corn afForrl rl snf corn attord good spe- cimens of very young IPIVPQ Ru /.nrofnll , "Pl'er portion of th leaf; p\ palisade tissue of th.i leaves. By carefully lo art of the ]eaf . . f /iUS Been in transverse removing the outer section. X 235. From a drawing by the author. leaves in succession all stages of leaf -development may be obtained. Fig. 134. Transverse section of the leaf of Silphvim i aci * latum . , f cp jdennis of the upper surface ; ', epi- of the lower surface ; p, palisade tiscue of the south i.e., with the leaf-planes parallel to the plane of the meridian- see articles in the American Naturalist : 1870, p. 495 ; 1871, p. 1 ; 1877, p. 480. 158 BOTANY. In tliis way often much light will be thrown upon the morphology of leaf parts.* (b) Among Dicotyledons it is generally best to select those whose _ young leaves are least downy or hairy, * * * * otherwise the difficulties of the examina- tion are greatly increased. The lilac is one of tbe liest for this purpose. Longi- tudinal sections, prepared as in the ex- amination of young stems, should be made. (c) The young leaves in the winter buds of the hickory are instructive, as showing Fig. 136. A part of a trans- verse section of the 1. af of fitipa gpartea in the position it as- sumes i.e., with what is really the upper surface turned toward the earth. /,/, rib*, each con chlorophyll-bearing paren (figured dark in the cut), (d) The study of the arrangement of between these are the masses of ?nchyma x leaves is most interesting in the twigs and cones of the Conifers, and the stems and heads of the Composites. The student should, however, before spending much time in the Fig 136. Transverse section of one of the ribs of the leaf of fitipa f/>artfa. tp, chlorophyll-bearing parenchyma ; , , portions of the epidermic eoattuniug stc.in;ita : t when the leaf rolls up. The blaiik ccupied by chlorophyll-bearin X 125. From a drawing by the author. , , he, he, hygroscopic cells, which contract when the leaf rolls up. The blaiik space on the left shows the extent of the cavity occupied by chlorophyll-bearing parenchyma. examination of the more difficult forms, study the twenty-sixth section of Sachs' "Text-Book of Botany," and the whole subject of the * In illustration of this, the Iris itself may be cited. Its leaf is usually spoken of as made by ihe folding of its upper surface upon THE ROOTS OF PLANTS. 159 arrangement of lateral members as given in Hofmeister's "General Morphology." * (e) Tlie internal structure of the leaf may be easily studied. The most important sections are those made at right angles to the surface ; but some should be made alt-o parallel to it, so as to show the form of the palisade cells and the dispositions of the cells in the loose tissue of the under surface. The leaves of the lilac, apple, cherry, Tmpatiens, Sttphium, sunflower, etc., are very good for this study. The more difficult sections can be more easily made after soaking the leaves for some time in strong alcohol, thus hardening them. VI. OF THE BOOTS OF PLANTS. 205. The root differs from all other members of the plant in being tipped with a peculiar mass of cells the Root- cap (pileorhiza f) and in originating cndogenously ; from stems it differs in never producing leaves or other phyllome structures. There is some doubt as to whether the Primary Root i.e., the first root of the embryo is not in many cases formed otherwise than endogenously ; J but all common roots certainly are developed from beneath the surface of other parts of the plant. 206. Roots may develop from any part of a plant which contains fibro-vascular bundles, so that it is no uncommon thing for them to issue from stems (particularly their nodes) and leaves, as well as from other roots. Whatever their origin, they are essentially alike, the differences, as before intimated, being of minor importance. They all agree in hav- itself, so that the two sides exposed to the air and light are said to be in reality the under surface. A study of the very young leaf of the Iris, along with that of Hemerocallis, shows them to be alike ; both are composed of an upper laterally flattened portion and a lower channelled one ; in the Iris the upper portion grows fully as much as the lower, while in Heinerocallis the growth is almost entirely confined to the lower portion, the upper extending but little and forming the small extremity of the leaf. The small tip of the leaf in the latter case is clearly the homologue of the whole of the so-called ensiform leaf of the former. * " Allgemeine Morphologic der Gewachse," von Wilhelm Hofmeis- ter ; Leipsig, 1868. f From the Greek m'AeoS, a cap, and frifa, a root. | The mode of formation of the Primary Root will be taken up for each group of plants in Part II. ICO BOTANY. ing less perfectly developed tissues and tissue systems. Their epidermal system is more feebly developed, and they bear very Fig. 137. Longitudinal section through the apex of a root of Indian corn (Zea mate). All within and above the line , , v, is the root proper, all below and ontnide of it is the root-cap, or ptleorhiza ; , apex of root ; e, e, epidermis, continued into the dermatogen at the apex ; v. v. the thickened outer wall of the epidermis (the origin of the root-cap from the dermatogen is not shown in this figure) ; sc, r, the cor- tex which if produced from the pcriblem at the apex ; m, g.f, the plerome; m be- comes the pith, g a vessel, f. wood ; a, a. outer and older portion of the root-cap ; i, inner and younger portion 'of the root cap. After Sach*. THE ROOTS OF PLANTS. 161 simple trichomes the root-hairs. The fibro-vascular bun- dles are, especially in the higher plants, of a much lower type than those in the stems and leaves. The fundamental system is also poorly developed, and has not that variety of tissues found in other portions of the plant. 207. Another remarkable peculiarity of roots is that they differ much less from one another in structure than do their steins. The young roots of Monocotyledons have very nearly the same structure that those of Dicotyledons have, and those of Pteridophytes do not differ much from either. The older roots of Monocotyledons and Dicotyledons differ considerably, on account of changes in their structure which take place later, and then each root bears a closer resemblance to the stem from which it grows, or to which it belongs. 208. The general structure of the root-cap may be easily understood from the accompanying figure (Fig. 137). It is a cap-like mass of parenchymatous cells which surrounds the end of the root ; its outer cells are loose, and in some cases are more or less changed into a mucilaginous mass; in any event they gradually lose their protoplasm and become detached and destroyed. The inner layers (i, s, Fig. 137) are constantly developing from a deep-lying tissue, the Dermato- gen* (not shown in the figure), so that as the cap is destroyed on the outside it is renewed from the interior. By its lat- eral growth it in some cases ensheathes the terminal part of the root for a considerable distance. 209. Back of the root-cap lies the primary meristem of the root, composed, in Phanerogams, of a mass of small and actively dividing cells. In this meristem there is as yet no differentiation, but as it is prolonged by rapid cell-multipli- cation the cells become modified in its posterior portion. There is thus a constantly advancing formation of meristem, followed at a little distance by as constant a modification into other tissues. The usual course of this differentiation is first into a central cylindrical mass, the Plerome\ (Fig. * From the Greek dipfia, SspnaroS, skin, and yswdu, to bring forth or generate. f So named by Hanstein (" Scheitelzellegruppe im Vegetationspunkt der Phanerogamen," 1868), from the Greek 7rA?/pu/ia, a filling up. 162 BOTANY. 137, m, f, g), which is ensheathed by the Periblem,* which soon becomes transformed into the cortical portion of the root (x, r, Fig. 137). The epidermis is developed from the region from which the root-cap grows, and, in fact, as will be shown below, it is a continuation and modification of the generating tissue of the root-cap. 21O. In Fig. 138 the relation of the parts is even better shown than in the previous figure. The central plerome column is surrounded by a layer of active cells, the pericam- pc Fig. 138. Median longitudinal sectipn of the apex of the root of the buckwheat (Fagopijrum eseulentiim). pc, pericambium, constituting the boundary of the plerome column ; e, dermatogen ; between e andpc, periblem ; 7t, root-cap. Alter De Bury. bium (pc) ; outside of the latter lies the periblem, or young cortical portion, and still outside of this the dermatogen (e), which further back on the root becomes the epidermis. The root-cap (h) lies entirely outside of, and is quite distinct from, the back portions of the dermatogen, but near the apex of the root there is a tract in which dermatogen and root-cap apparently fuse into one. At this point the layers * Another of Hanstein'8 terms, from the Greek 7rep!6?.iyia, a cloak. THE ROOTS OF PLANTS. 103 of the root-cap originate by the successive divisions of the dermatogen cells by partitions parallel to the curved surface of the root-tip. As the dermatogen is continuous with the epidermis, we may regard the root-cap as morphologically a greatly thickened and somewhat modified epidermis. Fig. 139. Mode of formation of the lateral roots in a mother-root of Trapa natans. A, a portionof the pericambium TT, bounded externally by the innermost layer of cor- tical cells, r; d. dermatogen ; n, the inner layer of the pericambium after splitting : Ji. the same advanced somewhat, the inner layer is beginning to divide; C, young root enclosed in the tissue of the mother-root ; Ji. r, cortex ormother-root ; IT, pen- cambium of mother-root, from which the new root has been formed ; h, first layer of the root-cap of the new root, formed by the splitting of its dermatogen 6 ; i, n, mass of cell- resulting from the division of the layer n in A ; D, new root further devel- oped (the thick cortical tissues of the mother-root are not shown ; r, inner layer of conical tissue of mother-root) ; p, p, periblem of new root ; m, m, the tissue which connects the new root with the tissues of the mother-ioot. Magnified. After Reiiike. The plerome column is a mass of nascent fibro-vascular elements, and in it, somewhat further back from the root-tip, a differentiation into the bundle takes place. 164 BOTANY. 211. The formation aiid development of a new root is interesting and suggestive. It usually takes place at some distance from the primary meristem, in the cambium or peri- cambium. In the root of Trapa natans it takes place as fol- lows : The cells of a restricted portion of the pericambium divide by tangential walls into an outer layer, which becomes the dermatogen of the new root (d, Fig. 139), and an inner layer, from which develops, its primary meristem (n, Fig. 139). The inner cells multiply by divisions in several direc- tions, and as their mass increases they push out the young dermatogen (B, C, and D, Fig. 139). From the dermato- gen the first layer of the root-cap is formed by the tangen- tial division of its cells (C, h, Fig. 139). These growing tissues push out the overlying portions of the mother-root, and finally break through them. The root is thus seen to be a strictly endogenous formation ; there is no connection between its tissues and the epidermal and cortical portions of the mother-root, the sole connection being with the deep- lying tissues in, or in connection with, the fibro-vascular bundles. Herein roots present a marked contrast to stems and leaves, which, as a rule, develop from the exterior of the plant-body, or, in other words, are exogenous in their origin. 212. Roots are rarely arranged in as regular an order as are stems. In general they arise in acropetal order upon the mother-roots of Pteridophytes and the primary roots of Pha- nerogams, but this order is subject to many more disturbing influences than in the case of the origin of stems. As to position, they may arise in rows or ranks, or in particular spots, dependent upon the disposition of the fibro-vascular bundles, or the generating tissues in the root or stem. Thus it may happen that on a root or stem there may be as many rows of roots as there are fibro-vascular bundles. Roots which develop from stems are generally much more affected by external influences than those which grow from other roots. The degree of moisture of the different parts of the stem appears to have much to do in determining the point of the appearance of roots ; this is seen in stems which touch the ground, as in the tomato, and in climbing plants. MS tin- THE ROOTS OF PLANTS. 165 Ivy (Hedera), Poison Ivy (Rhus), the Virginia Creeper (Am- pelopsis), etc. 213. In form roots are generally fibrous, and this is manifestly their best form, in so far as they are organs for obtaining dissolved matters from the soil. In perennials, however, as the stems become larger the roots increase cor- respondingly to support the additional weight ; they thus become hold-fasts or mechanical supports. In other cases they are made the recipients of assimilated matters, as starch, sugar, etc., and thus become thickened storehouses. In many cases the latter are capable of forming buds and of sending out new stems from the ineristem tissue in, or in the vicinity of, the fibre-vascular bundles, as is notably the case in the tuberous root of the SAveet potato. (a) The root-cap may be studied with the least difficulty in roots which are grown in water. Those of Lemna may be easily obtained, and are excellent. (b) Roots of Indian corn, Hyacinth, Impatiens, etc., also furnish easily made and good specimens. (e) In preparing specimens for examination thin longitudinal sections should be made, and these should be supplemented by transverse sec- tions taken at various heights on a root-tip. (d) By the use of staining fluids, as carmine, magenta, etc., some points in the structure will be made more evident. Iodine should also be used ; by treatment with it, the starch which is present in the root- tip in many, if not all, cases may be seen. (e) For studying the formation and development of new roots suc- culent plants should be chosen, as the sections of their tissues are more transparent than those of other plants. On this account many water plants are to be preferred. Anion