Goruell University Library Dthaca, New Pork COMSTOCK MEMORIAL LIBRARY ENTOMOLOGY BOUGHT WITH THE INCOME OF a FUND GIVEN BY THE STUDENTS OF JOHN HENRY COMSTOCK PROFESSOR OF ENTOMOLOGY 1915 Cornell University Libra Ti A COURSE OF PRACTICAL INSTRUCTION IN KLEMENTARY BIOLOGY. A COURSE OF PRACTICAL INSTRUCTION IN ELEMENTARY BIOLOGY BY \e? wr" T, H, HUXLEY, LLD., Sec. RS, ASSISTED BY H. N. MARTIN, BA, MB, D.Sc. FELLOW OF CHRIST’S COLLEGE, CAMBRIDGE. London: MACMILLAN AND CO, 1875. [All Rights reserved.} { ly oe Ae} Cambridge: PRINTED BY C. J, CLAY, M.A. AT THE UNIVERSITY PRESS. are \ Trcar yon a aS Meee ALY CAPT \ os! \ Own Tilieweder Tidy PREFACE. Very soon after I began to teach Natural History, or what we now call Biology, at the Royal School of Mines, some twenty years ago, I arrived at the conviction that the study of living bodies is really one discipline, which is divided into Zoology and Botany simply as a matter of convenience; and that the scientific Zoologist should no more be ignorant of the fundamental phenomena of vegetable life, than the scien- tific Botanist of those of animal existence. Moreover, it was obvious that the road to a sound and thorough knowledge of Zoology and Botany lay through Morphology and Physiology; and that, as in the case of all other physical sciences, so in these, sound and thorough knowledge was only to be obtained by practical work in the laboratory. M. b vi PREFACE, The thing to be done, therefore, was to organize a eourse of practical instruction in Elementary Biology, as a first step towards the special work of the Zoologist and Botanist. But this was forbidden, so far as I was concerned, by the limi- tations of space in the building in Jermyn Street, which possessed no room applicable to the purpose of a labora- tory; and I was obliged to content myself, for many years, with what seemed the next best thing, namely, as full an ex- position as I could give of the characters of certain plants and animals, selected as types of vegetable and animal organiza- tion, by way of introduction to systematic Zoology and Pale- ontology. In 1870, my friend Professor Rolleston, of Oxford, pub- lished his “Forms of Animal Life.” It appears to me that this exact and thorough book, in conjunction with the splendid appliances of the University Museum, leaves the Oxford student of the fundamental facts of Zoology little to desire. But the Linacre Professor wrote for the student of Animal life only, and, naturally, with an especial eye to the conditions which obtain in his own University; so that there was still room left for a Manual of wider scope, for the use of learners less happily situated. In 1872 I was, for the first time, enabled to carry my own notions on this subject into practice, in the excellent rooms provided for biological instruction in the New Buildings at PREFACE. vil South Kensington. In the short course of Lectures given to Science Teachers on this occasion, I had the great advantage of being aided by my friends Dr Foster, F.R.S., Prof. Ruther- ford and Prof. Lankester, F.R.S., whose assistance in getting the laboratory work into practical shape was invaluable. Since that time, the biological teaching of the Royal School of Mines having been transferred to South Kensing- ton, I have been enabled to model my ordinary course of instruction upon substantially the same plan. The object of the present book is to serve as a laboratory guide to those who are inclined to follow upon the same road. A number of common and readily obtainable plants and ani- mals have been selected in such a manner as to exemplify the leading modifications of structure which are met with in the vegetable and animal worlds. A brief description of each is given; and the description is followed by such detailed instructions as, it is hoped, will enable the student to know, of his own knowledge, the chief facts mentioned in the ac- count of the animal or plant. The terms used in Biology will thus be represented by clear and definite images of the things to which they apply; a comprehensive, and yet not vague, conception of the phenomena of Life will be obtained; and a firm foundation upon which to build up special know- ledge will be laid. The chief labour in drawing up these instructions has vill PREFACE. fallen upon Dr Martin. For the general plan used, and the de- scriptions of the several plants and animals, I am responsible; but I am indebted for many valuable suggestions and criti- cisms from the botanical side to my friend Prof. Thiselton Dyer. T. H. H. Lonpon, September, 1875. CONTENTS. I. YEAST. General characters—Fermentation—A ppearances of yeast under the micro- scope—Structure of yeast cells—Chemical composition—Mode of multiplication —Growth in Pasteur’s fluid—Physiology of yeast—Laboratory work. p. I—10. II. Prorococcus. Habitat—Histological structure—Modes of multiplication—Dependence on light—Physiology of Protococcus—Motile stage—Laboratory work. p. r1—16. If. PrRoreus ANIMALCULE. COLOURLESS BLOOD CORPUSCLES. Ames — Habitat — Movements — Structure — Chemical composition — Effects of temperature and electric shocks—Encystation—CoLOURLESS BLOOD CORPUSCLES—Movements—Structure—The influence of various reagents on them—Physiology of Ameba. Laboratory work. : + p. 17-23. IV. Bacteria. Form and structure—Movements—Spirillum volutans—Stationary stage— Zoogloea—Growth in Pasteur’s fluid—Relation to putrefaction—Power of resisting desiccation—Laboratory work, —. i : . + p. 24-28. x CONTENTS. Vv. . Moo.ps. Fungi—Their spores—PrnicibLiuM—Habitat—General characters—Form and structure—Development—Mucor—Habitat—Form and structure—Deve- lopment, asexual and sexual—Alternation of generations—Mucor Torula— Laboratory work. : : k : 2 Z + Pp. 29—40. VI. STONEWORTS. Habitat and general characters—Development—Mode of growth and micro- scopicstructure—Protoplasmic movements—Organs of reproduction—Physiology —Laboratory work. . Z 3 é é Pp: 41—53. VIL. Tue Bracken Fern. Habit—Structure, gross and microscopic—The various tissues—Mode of growth—Development— Prothallus—Sexual organs—Alternation of genera- tions—Laboratory work. . ‘ “ é 4 ‘ ‘ » Pp. 54-67. VIII. Ture Brean Puant. Habit— General structure—Development and mode of growth—Sexual organs—Homology with the reproductive organs of the Fern—Physiology— Laboratory work. a 3 : - : : . 5 - p. 68—85- IX. Tue Brett ANIMALCULE. Habit and distribution —Anatomy—Movements— Contractile vesicle— Ingestion—-Modes of multiplication— Encystation—Laboratory work. p- 86—g4. X. FRESH-WATER POLYPES. Habit and form—Naked eye appearances—Mode of feeding—Multiplication Microscopie structure — Relationships to simpler plants and animals — Laboratory work. , 2 : . : ‘ + Pp. 95—I03. CONTENTS. x1 XI. Tuer FRESH-WATER MusszEL. General structure—Respiratory organs—Alimentary organs—Circulatory system—Excretory organs—Reproductive organs—Development—Laboratory work. 1 : 3 5 ‘ & . + Pp. 104—I121. XII. THE FRESH-WATER CRAYFISH AND THE LOBSTER. Habitat—General structure—Appendages—Segments—Alimentary canal— Circulatory organs. —Respiratory organs—The Green glands—Nervous system —Sense organs— Reproductive organs—Development— Laboratory work. p. 122—151. XIII. Tue Froa. General characters—Development—Specific characters of Rana temporaria and &. esculenta—The pleuroperitoneal cavity and the alimentary canal—The neural canal and the cerebro-spinal axis—Objects seen on transverse sections at various points—Comparison with lobster—The skeleton—The digestive system—The blood and lymph vascular systems—The ductless glands—The respiratory organs—The urinary organs—The generative organs—The nervous system—The sense organs—Laboratory work. ‘ «pe 182—257. APPENDIX . : : , p- 258. YEAST (Torula or Saccharomyces Cerevisic). YEAST is a substance which has been long known on account of the power which it possesses of exciting the process termed Jermentation in substances which contain sugar. If strained through a coarse filter, it appears to the naked eye as a brownish fluid in which no solid particles can be discerned. When some of this fluid is added to a solution of sugar and kept warm, the mixture soon begins to disengage bubbles of gas and become frothy; its sweetness gradually disappears ; it acquires a spirituous flavour and intoxicating qualities; and it yields by distillation a light fluid—alcohol (or spirits of wine) which readily burns. When dried slowly and at a low temperature, yeast is reduced to a powdery mass, which retains its power of exciting fermentation in a saccharine fluid for a considerable period. If yeast is heated to the temperature of boiling water, be- fore it is added to the saccharine fluid, no fermentation takes place; and fermentation which has commenced is stopped by boiling the saccharine liquid. A saccharine solution will not ferment spontaneously. If it begins to ferment, yeast has undoubtedly got into it in some way or other. If the yeast is not added directly to the saccharine fluid, but is separated from it by a very fine filter, such as porous earthenware, the saccharine fluid will not ferment, although the filter allows the fluid part of the yeast to pass through into the solution of sugar. M. 1 2 ELEMENTARY BIOLOGY. [. If the saccharine fluid is boiled, so as to destroy the efficiency of any yeast it may accidentally contain, and then allowed to come in contact only with such air as has been passed through cotton wool, it will never ferment. But if it is exposed freely to the air, it is almost sure to ferment sooner or later, and the probability of its so doing is greatly increased if there is yeast anywhere in the vicinity. These experiments afford evidence (1) that there is some- thing in yeast which provokes fermentation, (2) that this something may have its efficiency destroyed by a high tem- perature, (3) that this something consists of particles which may be separated from the fluid which contains them by a fine filter, (4) that these particles may be contained in the air; and that they may be strained off from the air by causing it to pass through cotton wool. Microscopic examination of a drop of yeast shews what the particles in question are. Even with a hand-glass, the drop no longer appears homogeneous, .as it does to the naked eye, but looks as if fine grains of sand were scattered through it; but a considerable magnifying power (5—600 diameters) is necessary to shew the form and structure of the little granules which are thus made visible. Under this power, each granule (which is termed a Torula) is seen to be a round, or oval, transparent body, varying in diameter from 5—— * oth to aD th of an inch Te a). The Torule are either single, or associated in heaps or strings. Each consists of a thin-walled sac, or bag, containing a semi-fluid matter, in the centre of which there is often a space full of a more clear and watery fluid than the rest, which is termed a ‘vacuole.’ The sac is comparatively tough, but it may be easily burst, when it gives exit to its contents, (on the average about ——. 1] YEAST. 3 which readily diffuse themselves through the surrounding: fluid. The whole structure is called a ‘cell;’ the sac being the ‘cell-wall’ and the contents the ‘protoplasm.’ When yeast is dried and burned in the open air it gives rise to the same kind of smell as burning animal matter, and a certain quantity of mineral ash is left behind. Analysed into its chemical elements, yeast is found to contain Carbon, Hydrogen, Oxygen, Nitrogen, Sulphur, Phosphorus, Potassium, Magnesium and Calcium; the last four in very small quanti- ties. These elements are combined in different ways, so as to form the chief proximate constituents of the Torula, which are (1) a Protein compound, analogous to Casein, (2) Cellulose, (3) Fat, and (4) Water. The cell-wall contains all the Cellulose and a small proportion of the mineral matters. The protoplasm contains the Protein compound and the Fat with the larger proportion of the mineral salts. These Torule are the ‘particles’ in the yeast which have the power of provoking fermentation in sugar; it is they which are filtered off from the yeast when it loses its effi- ciency by being strained through porous earthenware; it is they which form the fine powder to which yeast is reduced by drying, and which, from their extreme minuteness, are readily diffused through the air in the form of invisible dust. That the Torule are living bodies is proved by the manner in which they grow and multiply. If a small quantity of yeast is added to a large quantity of clear saccharine fluid so as hardly to disturb its transparency, and the whole is kept in a warm place, it will gradually become more and more turbid, and, after a time, a scum of yeast will collect, which may be many thousand, or million, times greater in weight than that which was originally added. If the Torule are examined as this process of 1—2 4 ELEMENTARY BIOLOGY. [1. multiplication is going on, it will be found that they are giving rise to minute buds, which rapidly grow, assume the size of the parent Torula, and eventually become detached; though, generally, not until they have developed other buds, and these yet others. The Yorule thus produced by gem- mation, one from the other, are apt long to adhere together, and thus the heaps and strings mentioned, as ordinarily occurring in yeast, are produced. No Torula arises except as the progeny of another; but, under certain circumstances, multiplication may take place in another way. The Torula does not throw out a bud, but its protoplasm divides into (usually) four masses, each of them surrounds itself with a cell-wall, and the whole are set free by the dissolution of the cell-wall cf the parent. This is multiplication by endogenous division. As each of the many millions of Torule which may thus be produced from one Yorula has the same composition as the original progenitor, it follows that a quantity of Protein, Cellulose and Fat proportional to the number of Torule thus generated, must have been produced in the course of the operation. Now these products have been manufactured by the Torule out of the substances contained in the fluid in which they float and which constitute their food. To prove this it is necessary that this fluid should have a definite composition. Several fluids will answer the pur- pose, but one of the simplest (Pasteur’s solution) is the following. Water: sng shess discs ea (H,0). DUGAL. iiss tea seesane (C,H..0))s Ammonium Tartrate (C,H,(NH,),0,). Potassium Phosphate (KH,PO,). Calcium Phosphate — (Ca,P,O,). Magnesium Sulphate (MgSO,). In this fluid the Torudce will grow and multiply. But it 1] YEAST. 5 will be observed that the fluid contains neither Protein nor Cellulose, nor Fat, though it does contain the elements of these bodies arranged in a different manner. It follows that the Torula must absorb the various substances contained in the water and arrange their elements anew, building them up into the complex molecules of its own body. This is a property peculiar to living things. The Zorula being alive, the question arises whether it is an animal or a plant. Although no sharp line of demarcation can be drawn between the lowest form of animal and of veget- able life, yet Torula is an indubitable plant, for two reasons. In the first place, its protoplasm is invested by a continuous cellulose coat, and thus has the distinctive character of a vegetable cell. Secondly, it possesses the power of construct- ing Protein out of such a compound as Ammonium Tartrate, and this power of manufacturing Protein is distinctively a vegetable peculiarity. Zorula then is a plant, but it contains neither starch nor chlorophyll, it absorbs oxygen and gives off carbonic anhydride, thus differing widely from the green plants. On the other hand, it is, in these respects, at one with the great group of Fungi. Like many of the latter, its life is wholly independent of light, and in this respect, again, it differs from the green plants. Whether Zorula is connected with any other form of Fungi is a question which must be left open for the present. It is sufficient to mention the fact that under certain circum- stances some Fungi (e.g. Mucor) may give rise to a kind of Torula different from common yeast. The fermentation of the sugar is in some way connected with the living condition of the Torwla, and is arrested by all those conditions which destroy the life of the Torula and prevent its growth and reproduction. The greater part of the sugar is resolved into Carbonic anhydride and Alcohol, the elements of which, taken together, equal in weight those of the 6 ELEMENTARY BIOLOGY. [I. sugar. A small part breaks up into Glycerine and Succinic acid, and one or two per cent. is not yet accounted for, but is perhaps assimilated by the Torule. This is the more probable as Zorule will grow and multiply actively in a solution in which sugar and Ammonium Nitrate replace the Ammonium Tartrate of the former solution, in which case the carbon of the Protein, Cellulose and Fat manu- factured, must be obtained from the sugar. Moreover, though oxygen is essential to the life of the Torula, it can live in saccharine solutions which contain no free oxygen, appearing, under these circumstances, to get its oxygen from the sugar. It has further been ascertained that Zorule flourish remarkably in solutions in which sugar and pepsin replace the Ammonium Tartrate. In this case, the nitrogen of their protein compounds must be derived from the pepsin; and it would seem that the mode of nutrition of such Torule approaches that of animals. LABORATORY WORK. Sow some fresh baker’s yeast in Pasteur’s fluid* with sugar and keep it in a warm place: as soon as the mixture begins to froth up, and the yeast is manifestly increasing in quantity, it is ready for examination. 1 Pasteur's fluid; Potassium Phosph. Pree, Calcium Phosph. ......... oes ~ Magnesium Sulphate Ammonium Tartrate 100, [Cane sugar .............. 1500, J sWGHOr s,s; vise tes oeetesiaamincueiergeey 8576, 10,000 parts, The sugar is to be omitted when Pasteur’s fluid ‘without sugar” is ordered. Pasteur himself used actual yeast ash; the above constituents give an imitation ash, which, with the ammonium salt and sugar, answers all practical purposes, 1.] YEAST. 7 A. MorRpPHOLoGY. 1. Lo Spread a little out, on a slide, in a drop of the fluid, and examine it with a low power (4 inch objective) without a cover-glass. Note the varying size of the cells, and their union into groups. Cover a similar specimen with a thin glass and exa- mine it under a high power (4 or better } objective. Hartnack, No. 7 or 8, Oc. 3 or 4). Note the size (measure), shape, surface and mode of union of the cells, b. Their structure: sac, protoplasm, vacuole. a. Sac; homogeneous, transparent. 8. Protoplasm; less transparent; often with a few clear shining dots in it. y. Vacuole ; sometimes absent; size, position. é The relative proportion of sac, protoplasm, and vacuole in various cells. Draw a few cells carefully to scale. 3. Run in magenta solution under the cover-glass. (This is readily done by placing a drop of magenta solution in contact with one side of the cover-glass, and a small strip of blotting paper at the opposite side.) a. Note what cells stain soonest and most deeply, and what part of each cell it is that stains: the sac is unaffected; the protoplasm stained; the vacuole un- stained, though it frequently appears pinkish, being seen through a coloured layer of protoplasm. Burst the stained cells by placing a few folds of blotting paper on the surface of the cover-glass and pressing smartly with the handle of a mounted needle: note the torn empty and colourless, but solid and un- ELEMENTARY BIOLOGY. [I. crushed transparent sacs; the soft crushed stained protoplasm. Repeat observation 3, running in iodine solution instead of magenta. The protoplasm stains brown; the rest of the cell remains unstained. Note the absence of any blue coloration ; starch is therefore not present. Treat another specimen with potash solution, running it in as before: this reagent dissolves out the proto- plasm, leaving the sac unaltered. [Sow a few yeast-cells in Pasteur’s solution in a moist chamber and keep them under observation from day to day ; watch their growth and multiplication. ] [Endogenous division: take some yeast which has been grown in Pasteur’s solution at a temperature below 20° C.; spread it out in a thin layer on fresh cut potato slices or on some plaster of Paris, and place with wet blotting paper under a bell-jar: examine trom day to day with a very high power (800 diam.) for ascospores, which will probably be found on the fifth or sixth day.] B. PHYSIOLOGY. (Conditions and results of the vital activity of Torula.) 1. ae oe [e. Sow a fair-sized drop of yeast in— Distilled water. 10 per cent. solution of sugar in water. Pasteur’s fluid without the sugar. Pasteur’s fluid with sugar. Mayer’s pepsin solution’. ] 1 Mayer’s solution (with pepsin) = 15 per cent. solution of sugar-candy 20 ee. Dibydropotassic phosphate............ o'r grm. ° Calcie phosphate .....0.00......000...... o'lgrm. Magnesic sulphate PO PBUT seecotcloselaealy ves cutis toy ausavieunes o-23 erm. 1.] YEAST. 9 Keep all at about 35° C., and compare the growth of the yeast, as measured by the increase of the turbidity of the fluid, in each case. “a” will hardly grow at all, “b” better, “e” better still, “d’’ well, and “e” best of all. Note that bubbles of gas are plentifully evolved from both the solutions which contain sugar. That any growth at all takes place, in the case of experi- ments @ and b,is due to the fact that the drop of yeast added contains nutritious material sufficient to provide for that amount of growth. 2. Prepare two more specimens of “d” and keep one in a cold—the other in a warm (35°C.) place, but otherwise under like conditions. Compare the growth of the yeast in the two cases; it is much greater in the specimen kept warm. 3. Prepare two more specimens of “d”; keep both warm, but one in darkness, the other exposed to the light : that in the dark will grow as well as the other; sun- light is therefore not essential for the growth of Torula. 4. Sow some yeast-cells in Pasteur’s solution in a flask, the neck of which is closed by a plug of cotton wool, and heat to 100°C. for five minutes; then set it aside; no signs of vitality will afterwards be mani- fested by the yeast in the flask; it is killed by ex- posure to this temperature. 5. [Take two test tubes; in one place some yeast, with Pasteur’s solution containing sugar; in the other place baryta water, and then connect the two test tubes by tightly fitting perforated corks and a bent tube passing from above the surface of the fluid in the first tube to the bottom of the baryta water in the second; pass a narrow bent tube, open at both ends, through the cork of the baryta water 10 ELEMENTARY BIOLOGY. he tube, so that its outer end dips just below the surface of some solution of potash’. All gas formed in the first tube will now bubble through the baryta water in the second, and, from thence, any that is not absorbed will pass out through the potash into the air. An abundant precipitate of barytic carbonate will be formed which can be collected and tested. The fermenting fluid, therefore, evolves car- bonie anhydride. } 6. [Grow some yeast in Pasteur’s solution (with sugar), in a nearly closed vessel (say a bottle with a cork through which a long narrow open tube passes): as soon as the evolution of gas seems to have ceased, distil the fluid in a water bath and condense and collect the first fifth that comes over: redistil this after saturation with potassic carbonate, and test the distillate for alcohol by its odour and inflammability, and by the sulphuric acid and potassic dichromate test. | 7. [Determine that heat is evolved by a fluid in which active alcoholic fermentation is going on. Place 200 ce. of fresh yeast in a flask, and add 1 litre of Pasteur’s fluid with sugar: put another litre of the fluid alone in a similar flask, cover each flask with a cloth and place the two side by side in a place protected from draughts. When gas begins to be actively evolved from the yeast-containing solution, take the temperature of the fluid in each flask with a good thermo- meter; the temperature of the one in which fermentation is going on will be found the higher.] 1 The object of the potash is to shield the baryta water from any car- bonic acid that may be in the atmosphere, Il. PROTOCOCCUS (Protococcus pluvialis). Ir the mud which accumulates in roof-gutters, water- butts, and shallow pools, be collected, it will be found to contain, among many other organisms, specimens of Pro- tococcus. In one of the two conditions in which it occurs, Pro- tococcus is a spheroidal body a to roto of an inch in diameter, composed, like TZorula, of a structureless tough transparent wall, inclosing viscid and granular protoplasm. The chief solid constituent of the cell-wall is cellulose. The protoplasm contains a nitrogenous substance, doubtless of a proteinaceous nature, though its exact composition has not been determined, and indications of starchy matter are some- times to be found init. Either diffused through it, or collected in granules, is a red or green colouring matter (Chlorophyll). Individual Protococct may be either green or red; or half greer and half red; or the red and green colours may coexist in any other proportion. In addition to the single cells, others are found divided by partitions, continuous with the cellulose wall, into two or more portions, and the cells thus produced by fission become sepa- rate, and grow to the size of that form from which they started. Tn this manner Protococcus multiplies with very great rapidity, Multiplication by gemmation in the mode observed in Torula is said to occur, but is certainly of rare occurrence. 12 ELEMENTARY BIOLOGY. [II. The influence of sunlight is an essential condition of the growth and multiplication of Protococcus; under that in- fluence, it decomposes carbonic anhydride, appropriates the carbon, and sets oxygen free. It is this power of obtaining the carbon which it needs from carbonic anhydride, which is the most important distinction of Protococcus, as of all plants which contain chlorophyll, from Yorwla and the other Fungi. As Protococcus flourishes in rain-water, and rain-water contains nothing but carbonic anhydride, which it absorbs along with other constituents of the atmosphere, ammonium salts (usually ammonium nitrate, also derived from the air) and minute portions of earthy salts which drift into it as dust, it follows that it must possess the power of constructing protein by rearrangment of the elements supplied to it by their compounds. Torula, on the other hand, is unable to construct protein matter out of such materials. Another difference between Torula and Protococcus is only apparent: Torula absorbs oxygen and gives out carbonic anhydride; while Protococcus, on the contrary, absorbs carbonic anhydride and gives out oxygen. But this is true only so long as the Protococcus is exposed to sunlight. In the dark, Protococcus, like all other living things, undergves oxidation and gives off carbonic anhy- dride; and there is every reason to believe that the same process of oxidation and evolution of carbonic anhydride goes on in the light, but that the loss of oxygen is far more than covered by the quantity set free by the carbon-fixing apparatus, which is in some way related to the chlorophyll. The still condition of Protococcus, just described, is not the only state in which it exists. Under certain circumstances, a Protococcus becomes actively locomotive. The protoplasm withdraws itself from the cell-wall at all but two points, where it protrudes through the wall in the form of long vibratile filaments or cilia, and by the lashing of these cilia ‘ II.] PROTOCOCCUS. 13 the cell is propelled with a rolling motion through the water. The movement of the cilia is so rapid, and their substance is so, transparent and delicate, that they are invisible until they begin to move slowly, or are treated with reagents, such as iodine, which colour them. Not unfrequently the cell-wall eventually vanishes, and the naked protoplasm of the cell swims about, and may undergo division and multiplication in this state. Sooner or later, the locomotive form draws in its cilia, becomes globular, and, throwing out a cellulose coat, returns to the resting state. For reasons similar to those which prove the vegetable nature of Zorula, Protococcus is a plant, although, in its locomotive condition, it 1s curiously similar to the Monads among the lowest forms of animal life. But it is now known that many of the lower plants, especially i in the group of Algae, to which Protococcus belongs, give rise, under certain circum- stances, to locomotive bodies propelled by cilia, like the loco- motive Protococcus, so that there is nothing anomalous in the case of Protococcus. Like the yeast-plant, Protococcus retains its vitality after it has been dried. It has been preserved for as long as two years in the dry condition, and at the end of that time has resumed its full activity when placed in water. The wide distribution of Protococcus on the tops of houses and elsewhere, is thus readily accounted for by the transport of the dry Protococct by winds. 14 ELEMENTARY BIOLOGY. [1I. LABORATORY WORK. A. MorpPHOLoGy. a. Resting or stationary Protococcus. 1. Spread out some of the green matter in water, and put on a cover-glass. Examine first with a low, and then with a high power. Note the size, form, struc- ture, and colour of the cells. Size ; (measure)—very variable. Form; more or less spheroidal, with individual varia- tions. Structure ; sac—protoplasm—sometimes a vacuole-— sometimes apparently a nucleus. (Compare Torula, I. A. 2. 0b.) Colour ; generally green—sometimes red—sometimes half and half—sometimes centre red, periphery green—the colouring matter always in the pro- toplasm only—most frequently diffused, but sometimes in distinct granules. 2. Note especially the following forms of cell— a. The primitive or normal form. Roundish cells, with a cellulose sac, and unseg- mented granular contents. Draw several carefully to scale. Apply the methods of mechanical and chemical analysis detailed for Torula. (I. A. 3. 4. 5.6.) Note that iodine in some cells produces a blue coloration (? starch). Treat a specimen with iodine solution and then with sulphuric acid (75 per cent.): the sac will become stained blue. 11.] d. a PROTOCOCCUS. 15 Cells multiplying by fission : Simple fission. The protoplasm divides into two segments and then forms a_ partition dividing 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. B. Cells multiplying by budding, like Torula; rare. b. Motile stage. a. B. Mount a drop of water containing motile Proto- coccus, and examine with a high power. Note the minute, actively locomotive green bodies, of which two varieties can be distinguished. Small, green, pear-shaped cells. Run in iodine, which stains them and also kills them and stops their movements: note then the absence of any distinct sac, and the: two cilia attached to the narrower end. A form larger than the last and apparently intermediate to it and the still cells. Kill and stain with iodine as before. Note the central granular coloured (protoplasmic) portion—the loosely enveloping unstained sac —the two cilia prolonged from the protoplasm through an opening in the sac. c. Try to find specimens in which the movements are becoming sluggish, and see the cilia in motion. 16 ELEMENTARY BIOLOGY. pen [B. Puysroxoey. Get some water that is quite green from containing a large quantity of Protococcus; introduce some of it into two tubes inverted over mercury, and pass a smal] quantity of carbonic anhydride into each: keep one tube in the dark and place the other in bright sunlight for some hours. Then measure the gas in each tube and after- wards introduce a fragment of caustic potash into each ; the gas from the specimen kept in the dark will be more or less completely absorbed (= carbonic anhydride), that from the other will not be absorbed by the potash alone, but will be absorbed on the further introduction of a few drops of solution of pyrogallic acid (=oxygen). Protococcus, there- fore, in the sunlight, takes up carbonic anhydride and evolves oxygen. A comparative experiment may be made with a third tube containing water but no Protococcus. | IIT. THE PROTEUS ANIMALCULE (Ameba). COLOURLESS BLOOD CORPUSCLES. Amcebe are minute organisms of very variable size which occur in stagnant water, in mud, and even in damp earth, and are frequently to be obtained by infusing any animal matter in water and allowing it to evaporate while exposed to direct sunlight. An Ameba has the appearance of a particle of jelly, which is often more or less granular and fluid in its central parts, but usually becomes clear and transparent, and of a firmer consistency, towards its periphery. Sometimes Amcebec are found having a spherical form and encased in a structureless sac, and in this encysted state they exhibit no movements. More commonly, they present incessant and frequently rapid changes of form, whence the name of “ Proteus Animalcule” given to them by the older observers; and these changes of form are usually accompanied by a shifting of position, the Amoeba creeping about with considerable activity, though with no constancy of direction. The changes of form, and the movements, are effected by the thrusting out of lobe-lke prolongations of the peripheral part of the body, which are termed pseudopodia, sometimes from one region and sometimes from another. Occasionally, a particular region of the body is constantly free from pseu- M. 2 18 ELEMENTARY BIOLOGY. [III dopodia, and therefore forms its hindmost part when it moves. Each pseudopodium is evidently, at first, an extension of the denser clear substance (ectosarc) only ; but as it enlarges, the central, granular, more fluid substance flows into its interior, often with a sudden rush. In some Amobee a clear space makes its appearance, at intervals, in a particular region of the ectosarc, and then disappears by the rapid approach of its walls. After a while, a small clear speck appears at the same spot and slowly dilates until it attains its full size, when it again rapidly disappears as before. Sometimes two or three small clear spots arise close together, and run into one another to form the single large cavity. The structure thus described is termed the contractile vesicle or vacuole, and its rhythmical systole and diastole often succeed one another with great regularity. Nothing is certainly known respecting its function, nor even whether it does or does not communicate with the exterior, and thus pump water into and out of the body of the Amba, though there is some reason to think that this may be the case. Very frequently one part of the Ameba exhibits a rounded or oval body, which is termed the nucleus. This structure sometimes has a distinctly vesicular character, and contains a rounded granule called the nucleolus. The gelatinous body of the Amaba is not bounded by anything that can be properly termed a membrane; all that can be said is, that its external or limitary layer is of a somewhat different constitution from the rest, so that it acquires a certain appearance of distinctness when it is acted upon by such reagents as acetic acid, or when the animal is killed by raising the temperature to 45° C. Physically, the ectosarc might be compared to the wall of a soap-bubble, which, though fluid, has a certain viscosity, which not only 111. ] THE PROTEUS ANIMALCULE,. 19 enables its particles to hold together and form a continuous sheet, but permits a rod to be passed into or through the bubble without bursting it; the walls closing together, and recovering their continuity, as soon as the rod is drawn away. It is this property of the ectosare of the 4meba which enables us to understand the way in which these animals take in and throw out again solid matter, though they have neither mouth, anus, nor alimentary canal. The solid body passes through the ectosarc, which immediately closes up and repairs the rent formed by its passage. In this manner, the Amebe take in the small, usually vegetable, organisms, which serve them for food, and subsequently get rid of the un- digested solid parts. The chemical composition of the bodies of the Amebe has not been accurately ascertained, but they undoubtedly consist, in great measure, of water containing a protein com- pound, and are similar to other forms of protoplasm. They absorb oxygen and give out carbonic acid, and the presence of free oxygen is necessary to their existence. When the medium in which they live is cooled down to the freezing point their movements are arrested, but they recover when the temperature is raised. At a temperature of about 35° C. their movements are arrested, and they pass into a condition of “heat-stiffening,” from which they recover if that tempera- ture is not continued too long; at 40° to 45° C. they are killed. Electric shocks of moderate strength cause Amebw at once to assume a spherical still form, but they recover after a while. Strong shocks kill them. Not unfrequently, an active Amoeba becomes still spon- taneously, acquires a rounded form, and secretes a structure- less case or cyst, in which it remains enclosed for a shorter or longer period. If Amebe are not to be found, their nature may be understood by the examination of bodies, in many respects 2—2 20 ELEMENTARY BIOLOGY. [1n1. very similar to them, which occur in the blood of all verte- brate and most invertebrate animals, and are known as the ‘colourless corpuscles.’ They are to be met with in abun- dance in a fresh-drawn drop of human blood. In such a drop, after the red corpuscles have run into rolls, irregular bodies will be seen here and there in the meshes of the rolls. If one of these bodies is carefully watched it will be seen to undergo changes of form of the same character as those exhibited by Amebe, and these motions become much more active if the drop is kept at the temperature of the body by means of a hot stage. Each corpuscle is, in fact, a mass of protoplasm containing a nucleus, and the protoplasm sends out pseudopodia which are strictly comparable to those of Amabe. The colourless corpuscles, however, possess no contractile space. The colourless corpuscles of the blood of some of the cold-blooded vertebrates, such as Frogs and Newts, may be kept alive for many weeks in serum properly protected from evaporation; and if finely divided colouring matter, such as indigo, is supplied to them, either in the body or out of it, they take it into their interior in the same way as true Ameoebee would. In the earliest condition of the embryo, the whole body is composed of such nucleated cells as the colour- less corpuscles of the blood; and the colourless corpuscles must be regarded as simply the progeny of such cells, which have not become metamorphosed, and have retained the characteristics of the lowest and most rudimentary forms of - animal life. The Ameba is an animal, not because of its contractility or power of locomotion, but because it never becomes inclosed within a cellulose sac, and because it is devoid of the power of manufacturing protein from bodies of a comparatively simple chemical composition. The Ameba has to obtain its protein ready made, in which respect it resembles all true III.] THE PROTEUS ANIMALCULE. 21 animals, and therefore is, like them, in the long run, depend- ent for its existence upon some form or other of vegetable life. LABORATORY WORK. Place a drop of water containing Amebe on a slide, cover with a cover glass, avoiding pressure, and search over with + inch obj.: having found an Ameeba, examine with a higher power. 1. Size: differing considerably in different specimens. Measure. 2. Outline: irregular, produced into a number of thick rounded eminences (pseudopodia) which are constantly undergoing changes: sketch it at intervals of five seconds. 3. Structure: a. Outer hyaline border (ectosarc), tolerably sharply marked off: granular layer (endosarc) inside this, gradually passing into a more fluid central part. b. Nucleus: (absent in some specimens) ; a roundish more solid-looking particle, which does not change its form. c. Contractile vesicle : in the ectosare note a roundish clear space which disappears periodically, and after a time reappears ; its slow diastole—rapid systole. Not present in all specimens. d. Foreign bodies (swallowed); Diatom cases, Des- madre, &e. 22 ELEMENTARY BIOLOGY. [au 4. Movements: a. Watch the process of formation of a pseudopodium. A hyaline elevation at first ; then, as it increases in size, currents carrying granules flow into it. b. Locomotion: watch the process,—a pseudopodium is thrown out, and then the rest of the body is gradually drawn up to it. c. If the opportunity presents itself watch the pro- cess of the ingestion of solid matters. d. [Observe the movements on the hot stage; warmth at first accelerates the movements, but as the tem- perature approaches 40°C. they cease, and the whole mass remains as a motionless sphere. | e. [Effects of electrical shocks on the movements. | 5. Mechanical Analysis: crush. The whole collapses, ex- cept sometimes the nucleus, and even that after a time disappears: there is no trace of a distinct resisting outer sac. 6. Chemical Analysis: Treat with magenta and iodine. The whole stains, and there is no unstained enveloping sac. Iodine as a rule produces no blue coloration ; when blue specks become visible it is probable that the starch which they indicate has been swallowed. 7. [Look for encysted specimens: and for specimens which are undergoing fission. ] 8. Another form of Ameeba is not unfrequently found which differs from that just described in being much less coarsely granular, and in having no well-defined ectosare and endosarc, and also in having much longer, more slender and pointed pseudopodia. U1. THE PROTEUS ANIMALCULE. 23 B. Wuuire BLoop-CorPusciEs, (human). Prick your finger and press out a drop of blood: spread out on a slide under a coverslip, avoiding pressure, and surround the margin of the coverglass with oil. Neglect the pale yellow homogeneous (red) corpuscles, and examine the much less numerous, granular, colourless, ones. Note their— 1. Size: (measure). Form: changing much like that of the Amceba, but less actively. Draw at intervals of ten seconds. 3. Structure: Some more and some less granular; but no distinct ectosarc, endosarc, and vacuole as in the Ameba. Nucleus rarely visible in the fresh state. No contractile vesicle. 4. Treat with dilute acetic acid: the granules are cleared up, and a nucleus is brought into view in a more or less central position. Ifthe acetic acid has been too strong the nucleus will be constricted and otherwise distorted. 5. Stain with magenta, and iodine; the whole becomes coloured, the nucleus most intensely. 6. Place on the hot stage, and gradually warm up to 50°C. The movements are at first rendered more active, but ultimately cease, the pseudopodia-like processes being all retracted and the whole forming a motionless sphere. Let the specimen cool again ; the movements are not resumed; the protoplasm having passed into a state of permanent coagulation or rigidity. 7. Repeat the above observations on the white blood- corpuscles of the frog or newt. iv, BACTERIA. UNDER the general title of Bacterium a considerable variety of organisms, for the most part of extreme minuteness, are included. They may be defined as globular, oblong, rod-like or spirally coiled masses of protoplasmic matter enclosed in a more or less distinct structureless substance, devoid of chloro- phyll and multiplying by transverse division. The smallest are not more than th of an inch in diameter, so that 1 30000 under the best microscopes they appear-as little more than mere specks, and even the largest have a thickness of little more than {0000 a 00 th of an inch, though they may be very long in proportion. Many of them have, like Protococcus, two conditions —a still and an active state. In their still con- dition, however, they very generally exhibit that Brownian movement which is common to almost all very finely divided solids suspended in a fluid. But this motion is merely oscillatory, and is readily distinguishable from the rapid translation from place to place which is effected by the really active Bacteria. In one of the largest forms, Spirillum volutans, it has been possible to observe the cilia by which the movement is effected. In this there is a cilium at each end of the Iv.] BACTERIA. 25 spirally coiled body. No such structure, however, can be made out in the straight Bacteria, and it remains doubtful whether they possess cilia which are too fine to be rendered visible by our microscopes, or whether their movements are due to some other cause. Many forms, such as the Vibriones, so common in putrefying matters, appear obviously to have a wriggling or serpentiform motion, but this is an optical de- lusion. In this Bacterium, as in all others, the body does not rapidly change its form; but its joints are bent zig-zag-wise, and the rotation of the zig-zag upon its axis, as it moves, gives rise to the appearance of undulatory contraction. A cork- screw turned round, while its point rests against the finger, gives rise to just the same appearance. Bacteria, in the still state, very often become surrounded by a gelatinous matter, which seems to be thrown out by their protoplasmic bodies, and to answer to the cell-wall of the resting Protococcus. This is termed the Zooglea form of Bacterium. Bacteria grow and multiply in Pasteur’s solution (without sugar) with extreme rapidity, and, as they increase in number, they render the fluid milky and opaque. Their vital actions are arrested at the freezing point. They thrive best in a temperature of about 30°C. but, in most fluids, they are killed by a temperature of 60°C. (140° F.). In all these respects Bacteria closely resemble Torule ; and a further point of resemblance lies in the circumstance that many of them excite specific fermentative changes in substances contained in the fluid in which they live, just as yeast excites such changes in sugar. All the forms of putrefaction which are undergone by animal and vegetable matters are fermentations set up by Bacteria of different kinds. Organic matters freely exposed to the air are, in themselves, nowise unstable bodies, and, if due precautions have been taken to exclude Bacteria, they do not 26 ELEMENTARY BIOLOGY. [Iv. putrefy, so that, as has been well remarked, “putrefaction is a concomitant not of death, but of life.” Bacteria, like Torule and Protococct, are not killed by dry- ing up, and from their excessive minuteness they must be carried about still more easily than Zorule are. In fact there is reason to believe that they are very widely diffused through the air, and that they exist in abundance in all ordinary water and on the surface of all vessels that are not chemically clean. They may be readily filtered off from the air, however, by causing it to pass through cotton wool. LABORATORY WORK. 1. Infuse some hay in warm water for half an hour— filter, and set aside the filtrate: note the changes which go on in it—at first clear, in 24 or 36 hours it becomes turbid; later on, a scum forms on the sur- face and the infusion acquires a putrefactive odour. 2. Rub some gamboge down in water and examine a drop of the mixture with a high power: avoid all currents in the fluid and watch the Brownian move- ments; note that they are simply oscillatory—not translative. 3. Take a drop of fluid from a turbid hay infusion and examine it, using the highest power you have; in it will be found muititudes of Moving Bacteria. Note their— a. orm; elliptic or rodlike—sometimes forming short (2—8) jointed rows. Iv.] d. BACTERIA. 27 Size; breadth, very small but pretty constant ; length, varying, but several times greater than ‘their breadth.: measure. Structure ; an outer more transparent layer enve- loping less transparent matter: in the compound forms the envelope alone appears where two joints come in contact, so that the rod looks as if made up of alternating transparent and more opaque substances Movements ; some vital, and some purely physical (Brownian). The former various but progressive : the latter, a rotatory movement round a sta- tionary centre; study it in a drop of boiled infusion in which the Bacteria are all dead. Treat with iodine—only the more opaque parts stain ; probably then we have to do with protoplasm, enve- loped in non-protoplasmic matter. Resting Bacteria. (Zoogloea-stage.) a. Examine the scum from the surface of a hay infusion; it exhibits myriads of motionless Bac- teria, embedded in gelatinous material. Treat with iodine; the Bacteria stain as before: the gelatinous uniting material remains un- stained, Mixed with the Bacteria proper, both in the pellicle and the fluid beneath, may be found the following forms of living beings. a. Micrococcus. Bodies much like Bacteria, but short and rounded, and occurring singly, or in bead-like rows. They may be found free or in a Zoogloea stage. “TI ELEMENTARY BIOLOGY. [Iv. b. Bacillus. Threads composed of straight cylindri- cal joints much longer than those of Bacteria, but of a similar structure: they are always free- swimming. c. Vibrio. Like Bacillus, but with bent joints. d. Spirillum. Elongated unjointed threads rolled up into a more or less perfect spiral: frequently two spirals intertwine. In some of the largest forms a vibratile cilium can be made out on each end of the thread. e. Spirochete. Much like spirillum, but longer and with a much more closely rolled spiral. A very actively motile but not common form, Examine various putrefying fluids for Bacteria and related organisms. Place some fresh-made hay infusion in three flasks; boil two of them for three or four minutes, and while one is boiling briskly stop its neck with a plug of cotton-wool: leave the necks of the other two flasks unclosed, and put all three away in a warm place. a. Ina day or two abundant Bacteria will be found in the unboiled flask. b. In the boiled but unclosed flask Bacteria will also appear, but perhaps not quite so soon as in a. c. In the flask which has been boiled and kept closed Bacteria will not appear, if the experiment has been properly performed, even if it be kept for many months. Vv. MOULDS (Penicillium and Mucor). Torula, Protococcus and Ameba are extremely simple con- ditions of the two great kinds of living matter which are known as Plants and Animals. No plants are simpler in structure than Zorula and Protococcus, and the only animals which are simpler than Amabe, are essentially Amabw devoid of a nucleus and contractile vesicle. Moreover, how- ever complicated in structure one of the higher plants may be in its adult state, when it commences its existence it is as simple as Torula or Protococcus, or at most as Yorula or Pro- tococcus would be if it possessed a distinct nucleus; and the whole plant is built up by the fissive multiplication of the simple cell in which it takes its origin, and by the subsequent growth and metamorphosis of the cells thus produced. The like is’ true of all the higher animals. They commence as nucleated cells, essentially similar to Amcebe, and colourless blood-corpuscles, and their bodies are constructed by aggre- gations of metamorphosed cells, produced by division from the primary cell. It has been seen that Torula and Protococcvs, similar as they are in structure, are distinguished by certain important physiological peculiarities ; and the more compli- cated plants are divisible into two series, one produced by the growth and modification of cells which have the physiological peculiarities of Zorula and contain no chlorophyll, while the 30 ELEMENTARY BIOLOGY. [v. other, and far larger, series present chlorophyll, and have the physiological peculiarities of Protococcus. The former series comprises the Fungi, the latter all other plants; only a few parasitic forms among these being devoid of chlorophyll. The Fungi take their origin in spores, a kind of cells, which, however much they may vary in the details of their structure, are essentially similar to Torulew. Indirectly or directly, the spore gives rise to a long tubular filament, which is termed a hypha, and out of these hyphe the Fungus is built up. One of the commonest Moulds, the Penicillium glaucum, which is familiar to every one from its forming sage-green crusts upon bread, jam, eld boots, &c. affords an excellent and easily studied example of a Fungus. When examined with a magnifying glass, the green appearance is seen to be due, in great measure, to a very fine powder which is detached from the surface of the mould by the slightest touch. Beneath this lies a felt-work of delicate tubular filaments, the hyphe, forming a crust like so much blotting-paper, which is the mycelium. From the free surface of the crust innumerable hyphe project into the air and bear the green powder. These are the aérial hyphe. On the other hand, the attached surface gives rise to a like multitude of longer branched hyphe, which project into the fluid in which the crust is growing, like so many roots, and may be called the submerged hyphe. If the patch of Penicillium has but a small extent relatively to the surface on which it lies, multitudes of silvery hyphe will be seen radiating from its periphery and giving off many submerged, but few or no vertical, or sub- aérial, branches. Submitted to microscopic examination, a hypha is seen to be composed of a transparent wall (which has the same ‘characters as the cell-wall of Torula) and proto- plasmic contents, which fill the tube formed by the wall, and present large central clear spaces, or vacuoles. At intervals, v.] MOULDS. 31 transverse partitions, continuous with the walls of the tube, divide it into elongated cells, each of which contains a correspondingly elongated protoplasmic sac, or primordial utricle. The hyphe frequently branch dichotomously; and, in the crust, they are inextricably entangled with one another ; but every hypha, with its branches, is quite distinct from every other. Those aérial hyphze which are nearest the periphery of the crust end in simple rounded extremities ; but the others terminate in brushes of short branches, and each of these branches, as it grows and elongates, becomes divided by transverse constrictions into a series of rounded spores arranged like a row of beads. The spores formed in this manner are termed conidia. At the free end of each fila- ment of the brush the conidia become very loosely adherent, and constitute the green powdery matter to which re- ference has been made. Examined separately, a contdium is seen to be a spherical body, composed of a transparent sac, enclosing a minute mass of protoplasm, in all essential respects similar to a Zorula. If sown in an appropriate medium, as for example Pasteur’s solution, with or without sugar, the contdiwm germinates. Upon from one to four points of its surface an elevation or bulging of the cell-wall and of its contained protoplasm appears. This rapidly in- creases in length, and, continually growing at its free end, gives rise to a hypha, so that the young Penscillium assumes the form of a star, each ray being a hypha. The hyphe elongate, while side branches are developed from them by out- growths of their walls; and this process is repeated by the branches, until the hyphe proceeding from a single conidium. may cover a wide circular area, as a patch of mycelium. When, as is usually the case, many conidia germinate close together, their hyphe cross one another, interlace, and give rise to a papyraceous crust. After the hyphe have attained a certain length, the protoplasm divides at intervals, and 32 ELEMENTARY BIOLOGY. [v. transverse septa are formed between the masses thus divided off from one another. But neither in this, nor in any other Fungus, are septa formed in the direction of the length of the hypha. Very early in the course of the development of the . mycelium, branches of the hyphe extend downwards into the medium on which the mycelium grows; while, as soon as the patch has attained a certain size, the hyphe in its centre give off vertical aérial branches, and the development of these goes on, extending from the centre to the periphery. The outgrowth of pencil-like bunches of branches at the end of these takes place in the same order; and these branches, becoming transversely constricted as fast as they are formed, break up into conidia, which are ready to go through the same course of development. The conidia may be kept for a very long time in the dry state, without their readiness to germinate being in any way impaired, and their extreme minuteness and levity enable them to be dispersed and carried about by the slightest currents of air, The persistence of their vitality is subject to nearly the same conditions of temperature as that of yeast. Not unfrequently Zorule make their appearance, in abun- dance, among the hyphe and conidia of Penicillium, and appear to be derived from them; but it is still a disputed point, whether they are so or not. If some fresh horse-dung be placed in a jar and kept moderately warm, its surface will, in two or three days, be covered with white cottony filaments, many of which rise vertically into the air, and end in rounded heads, so that they somewhat resemble long pins. The organism thus produced is another of the Winigl aie mould termed Mucor mucedo. Each rounded head is a sporangium; the stalk on which it is supported rises from one of the filaments which ramify in * MOULDS. 33 the substance of the horse-dung, and are the hyphe. Each hypha is, as in Penicellium, a tube provided with a tough thickish structureless wall, which is partly composed of cel- lulose, and is filled by a vacuolated protoplasm. In old specimens, transverse partitions, continuous with the walls of the hyphe, may divide them into chambers or cells. The stalk of the sporangium is a hypha of the same structure as the others. The wall of the sporangium is beset with minute asperities composed of oxalate of lime, and it contains a great number of minute oval bodies, the spures. held together by a transparent intermediate substance. When the spo- rangium is ripe, the slightest pressure causes its thin and brittle coat to give way, and the spores are separated by the expansion of the intermediate substance, which readily swells up and finally dissolves, in water. The greater part of the wall of the sporangium then disappears, but a little collar, representing the remains of its basal part, frequently adheres to the stalk. The cavity of the stalk does not com- municate with that of the sporangium, but is separated from it by a partition, which bulges into the cavity of the sporangium, forming a central pillar or projection. This is termed the columella and stands conspicuously above the collar, when the sporangium has burst and the spores are evacuated. The spores are oval and consist of a sac, having the same composition as the wall of the hypha, which incloses a mass of protoplazm. When they are sown in an appropriate medium, as for example in Pasteur’s solution, they enlarge, become spheroidal, and then send out several thick prolonga- tions. Each of these elongates, by constant growth at its tree end, and becomes a hypha, from which branches are given off, which grow and ramify in the same way. As all the ramifying hyphe proceed from the spore as a centre, their development gives rise, as in Penicillium, to a delicate M. 3 RE ELEMENTARY BIOLOGY. [v. stellate mycelium. At first, no septa are developed in the hyphe, so that the whole mycelium may be regarded as a single cell with long and ramified processes, and the Mucor, at this stage, is an unicellular organism. From near the centre of the mycelium a branch is given off from a hypha, rises vertically, and after attaining a certain length ceases to elongate. Its free end dilates into a rounded head, which gradually increases in size, until it attains the dimensions of a full-grown sporangium ; and, at the same time, the proto- plasm contained in this head becomes separated from that in the stalk by a septum, which is curved towards the cavity of the sporangium, and constitutes the columella. The wall of the sporangium, thus formed, becomes covered externally with a coat of oxalate of lime spines. As the sporangium increases in size, its protoplasmic contents become marked out into a large number of small oval masses, which are close together, but not in actual contact. Each of these masses next becomes completely separate from the rest, surrounds itself with a cellular coat, and becomes a spore; while the pro- toplasm not thus used up in the formation of spores, appears to give rise to the gelatinous intermediate substance, which swells up in water, referred to above. The walls of the spores become coloured, and that of the sporangium gradually thins, until it is reduced to little more than the outer crust of oxalate of lime. The sporangium now readily bursts, and the spores are separated by the swelling and eventual dissolution of the gelatinous intermediate matter. Sporangia, in which spores are produced by division of the protoplasm, are com- monly termed ascz, and the spores receive the name of asco- spores. There appears to be no limit to the extent to which the Mucor may be reproduced by this process of asexual develop- ment of spores, by the fission of the contents of the sporang- ium; nor does any other mode of multiplication become vl MOULDS, 35 apparent, so long as the mould grows in a fluid medium and is abundantly supplied with nourishment. But when growing in nature, in such matters as horse- dung, a method of reproduction is set up which represents the sexual process in its simplest form. Adjacent hyphee, or parts of the same hypha, give off short branches, which become dilated at their free ends, and approach one another, until these ends are applied together. The protoplasm in each of the dilated ends becomes separated by a septum from that of the rest of the branch ; the two cells thus formed open into one another by their applied faces, and their protoplasmic contents becoming mixed together, form one spheroidal mass, to the shape of which the coalesced cell-membranes adapt themselves. This process of conjugation evidently represents that of sexual impregnation among higher organisms, but as there is no morphological difference between the moditied hyphe which enter into relation with one another, it is impossible to say which represents the male, and which the female, element. The product of conjugation is termed a zygospore. Its cellulose coat becomes separated into an outer layer of a dark blackish hue, the exosporium, and an inner colourless layer, the endosporium. The outer coat is raised into irregular elevations, to which corresponding elevations of the inner coat correspond. Placed in favourable circumstances, the zygospore does not immediately germinate; but, after a longer or shorter period of rest, the exosporium and the endosporium burst, and a bud-like process is thrown out, which, usually, grows only into a very short unbranched hypha. From this hypha a vertical prolongation is developed, which becomes converted into a sporangium, such as that already described, whence spores are produced, which give rise to the ordinary stellate mycelium. Thus, Mucor presents what is termed an “ alter- nation of generations”. The zygospore resulting from a 3—2 39 ELEMENTARY BIOLOGY. [v. sexual process developes into a rudimentary mycelium, with a single sporangium which constitutes the first generation (A). This gives rise, by the asexual development of spores in its sporangium, to the second generation (B), represented by as many separate Mucores as there are spores. The second generation (B) may give rise sexually to zygospores and so reproduce the generation (A); but, more usually, an indefi- nite series of generations similar to (B) are produced from one another asexually, before (4) returns. When Mucor is allowed to grow freely at the surface of a saccharine liquid, it takes on no other form than that de- scribed; but, if it be submerged in the same liquid, the mode of development of the younger hyphe becomes changed, They break up, by a process of constriction, into short lengths, which separate, acquire rounded forms, and at the same time multiply by budding after the manner of Torule. Coincidentally with these changes, an active fermentation is excited in the fluid, so that this “ Mucor-Torula,” function- ally as well as morphologically, deserves the name of ‘ yeast.’. If the Mucor-Torula is filtered off from the saccharine solution, washed, and left to itself in moist air, the Torule give off very short aérial hyphee, which terminate in minute sporangia. In these a very small number of ordinary mucor spores is developed, but, in essential structure, both the sporangia and the spores resemble those of normal J/ucor. v.] MOULDS, 37 LABORATORY WORK. J, PENICILLIUM. Prepare some Pasteur’s fluid, and leave it exposed to the air in saucers in a warm place: if Penicillium spores are at hand add a few to the fluid in each saucer: if spores cannot be obtained, the fluid, if simply left to itself, will probably be covered with Penicilliwm in ten days or a fortnight. Sometimes, however, the fluid will overrun with Bacteria, to the exclusion of everything else. And very frequently other moulds, such as Aspergillus, or Mucor, may appear instead of or along with Penicillium. 1. NAKED-EYE CHARACTERS. Note the powdery-looking upper surface, white in young specimens, pale greenish in older, and later still becoming dark sage-green : the smooth pale under surface: the dense tough character of the mycelium. 2. HISTOLOGICAL STRUCTURE. a. The mycelium. a. Tease a bit out in water, and examine first with low, and then with a high power: it is chiefly made up of interlaced threads or tubes—the a. Hyphae. Note their diameter (measure)—form —subdivisions (cells)—dichotomous mode of branching—and structure: the external homo- geneous sac; the granular less transparent pro- toplasm; the small round vacuoles. Draw. 38 ELEMENTARY BIOLOGY. lv. B. The intermixed Torule. Note their size and number. b. Hold a bit of the mycelium between two pieces of carrot, and cut a thin vertical section with a sharp razor: mount in water and examine with low and high power. b. The submerged hyphae. Small branched threads hanging down from the under surface of the mycelium: repeat the observations 2. &. a. a. c. The aérial hyphe and conidiophores. Tease out in water a bit from the surface of one of the greenish patches; observe the difficulty with which water wets it. Examine with low and high power. Note ;— a. The primary erect hypha. 8. Its division into a number of branches. y. The division of the terminal branches by con- strictions into a chain of conidia. Draw. d. The conidia. a. Their Stze (measure). Form ; spherical. Structure ; sac, protoplasm, vacuole. b. Stain with magenta and iodine. c. Treat another specimen with potash. e. The germination of the Conidia, and building up of the Mycelium. a. Sow some conidia in Pasteur’s fluid in a watch-glass ; protect from evaporation, and watch the development MOULDS. 39 of the mycelium (examine the surface with a low power); then the formation of aérial hyples finally the production of new conidia. [Sow conidia in Pasteur’s fluid in a moist chamber, and watch from day to day; note the formation of eminences at one or more points on a conidium; the elongation of these eminences to form hyphe ; the branching and inter- lacement of the hyphe. ] B. MUCOR MUCEDO. 1. te oo Place some fresh horse-dung under a bell-jar and keep moist aud warm; in from 24 to 48 hours its surface will nearly always be covered by a crop of erect aérial mucor-hyphe, each ending in a minute enlargement (sporangium) just visible with the un- assisted eye: it is this first crop of hyph and spor- anges which is to be examined. Snip off a few of the hyphz with a pair of scissors, mount in water, and examine with 1 inch obj. a. Large unbranched hyphe, each ending in a spherical enlargement (sporangiwm). Examine with { obj. The hyphe. a. Their size; they greatly exceed the hyphe of Penicillium both in length and diameter. B. Their structure; homogeneous sac, granular protoplasm, vacuoles: septa absent except close to the sporange. y. Treat with iodine and magenta; the proto- plasm is stained. 40 6. ELEMENTARY BIOLOGY. [v. Treat another specimen with Schultze’s solu- tion; the wall is stained violet. b. The sporangia or asci. Examine with } obj. a. b. C. Their size and form. Their structure. The homogeneous enveloping sac covered by irregular masses of calcic oxalate. The granular protoplasmic contents: un- segmented in some; divided into a_ great number of distinct oval masses (ascospores) in others. The projection into the sporangial cavity of the convex septum (columella) which separates the hypha from the sporange. The collar projecting around the base of the columella of burst sporangia. Stain some with iodine; others with Schultze’s solution. c. The ascospores. a 7» 2 @B & Crush some ripe asci by gentle pressure upon the cover-glass. Examine with 4 obj. The size of the ascospores (measure). Their form ; cylindrical and elongated. Their structure. Stain with iodine and magenta. VI. STONEWORTS (Chara and Nitella). THESE water-weeds are not uncommonly found in ponds and rivers, growing in tangled masses of a dull green colour. Each plant is hardly thicker than a stout needle, but may attain a length of three or four feet. One end of the stem is fixed in the mud at the bottom, by slender thread-like roots, the other floats at the surface. At intervals, appendages, consisting of leaves, branches, root-filaments, and reproductive organs, are disposed in circles, or whorls. In the middle and lower parts of the plant these whorls are disposed at considerable and nearly equal distances ; but, towards the free upper end, the intervals between the whorls diminish, and the whorled appendages themselves become shorter, until, at the very summit, they are all crowded together into a terminal bud, which requires the aid of the microscope for its analysis. The parts of the stem, or aas, from which the append- ages spring are termed nodes ; the intervening parts being internodes. When viewed with a hand-magnifier the inter- nodes exhibit a spiral striation. In Chara, each internode consists of a single, much-elongat- ed cell, which extends throughout its whole length, invested by a cortical layer, composed of many cells, the spiral ar- rangement of which gives rise to the superficial marking which has been noted. And this multicellular structure is continued from the cortical layer, across the stem, at each node. The stem therefore consists of a series of long, axial cells, contained in as many closed chambers formed by the 42 ELEMENTARY BIOLOGY. [VI small cortical cells. The nodes are the multicellular parti- tions between these chambers. The branches are altogether similar in structure to the main stem. The leaves are also similar to the stem, so far as they consist of axial and cortical cells, but they differ in the form and_ proportions of these cells, as well as in the fact that the summit, or free end, of the leaf is always a much-elongated pointed cell. The branches spring from the re-entering angle between the stem and the leaf, which is termed the azilla of the leaf; and, in the same position, at the fruiting season of the plant are found the reproductive organs. These are of two kinds, the one large and oval, the sporangia or spore- fruits, the other smaller and globular, the antheridia Both, when ripe, have an orange-red colour, and are seated upon a short stalk. If a growing plant be watched, it will be found that it constantly increases in length in two ways. New nodes, internodes, and whorls of appendages are constantly be- coming obvious at the base of the terminal bud; and these appendages increase in size and become more and more widely separated, until they are as large and as far apart as in the oldest parts of the plant. The appendages at first consist exclusively of leaves and root-filaments (rhizords), and it is only when these have attained their full size that branches, epore-fruits and antheridia are developed in their axillz. Sometimes rounded cellular masses appear in the axillee of the leaves, and, becoming detached, grow into new plants. These are comparable to the bulbs of higher plants. If the innermost part of the terminal bud, which con- stitutes the free end of the axis, or stem, be examined, it will be found to be formed by a single nucleated cell, separated by a transverse septum from another. Beneath this last follows another cell, which has already undergone wi.) STONEWORTS. 43 division into several smaller cells by the development. of longitudinal septa. This is the most newly-formed node. Below this again is a single cell, which is both longer and broader than those at the apex, and is an internodal cell. Below it follows another node, composed of more numerous small cells than in the first. Some of the peripheral cells of this node are undergoing growth and division, and thus give rise to cellular prominences, which are the rudiments of the first whorl of leaves. In the still lower parts of the stem the internodal cells get longer and longer, but they never divide. The nodal cells, on the other hand, multiply by division, but do not greatly elongate. From the first, the nodal cells overlap the internodal cell, so as to meet round its equator, and thus completely invest it externally. And, as the internodal cell grows and elongates, the overlapping parts of the nodes increase in length and become divided into internodal and nodal cells, which take on a spiral arrangement, and thus give rise to the cortical layer. Thus the whole plant is composed of an aggregation of simple cells; and, while it lives, new nodes and internodes are continually being added at its summit, or growing point. The internodal cells which give rise to the centre of the stem undergo no important change, except great increase of size, after they are once formed. The nodal cells, on the contrary, undergo division with comparatively little in- crease in size. And out of them, the nodes, the cortical layer, and all the appendages, are developed. In all the young cells of Chara a nucleus of relatively large size is to be seen imbedded in the centre of the protoplasm, which is motionless, and is inclosed in a struc- tureless cell-wall, containing cellulose. As the cell grows larger, the centre of the protoplasm becomes occupied by a watery fluid, and its thick periphery, which remains applied against the cell-wall, constitutes the wall of a sac, or 44 ELEMENTARY BIOLOGY. [vI. primordial utricle, m which the nucleus is imbedded. In the larger cells the primordial utricle is readily detached and made to shrivel up into the middle of the cell by treatment with strong alcohol. Numerous small green bodies—chlorophyll grains—are imbedded in the outer, or superficial, part of the primordial utricle. And they increase in number by division, as the cell enlarges. These chlorophyll grains are composed of proto- plasmic matter, which frequently contains starch granules, and is impregnated with the green colouring substance. During life, the layer of the primordial utricle which lies next to the watery contents of all the larger cells is in a state of incessant rotatory motion, while the outermost layer which contains the chlorophyll grains is quite still. In the large cells, so long as the nucleus is discernible, it is carried round with the rotating stream. The antheridium is a globular spheroidal body with a thick wall, made up of eight pieces, which are united by interlocking edges. The four pieces which make up the hemi- sphere to which the stalk of the antheridium is attached, are foursided, the other four are triangular. From the centre of the inner, concave face of each piece a sort of short process, the handle or manubriwm, projects into the cavity of the hollow sphere. At the free end of the manubrium is a rounded body, the capitulum, which bears six smaller, second- ary capitula ; and each secondary capitulum gives attachment to four long filaments divided by transverse partitions into a multitude (100 to 200) of small chambers. Thus, there may be as many as 20,000 to 40,000 chambers in each antheridium (8 x 6 x 4x 100 or x 200). The several pieces of which the wall of the antheridium is composed, the manubrium, the capitula, the secondary capitula and the chambers of the filaments, are all more or less modified cells, as may be proved by tracing the antheridia from their earliest condition, as vi] STONEWORTS. 45 small processes of the nodal region, to their complete form. The cells of the filaments are, at first, like any other cells; but, by degrees, the protoplasm of each becomes changed into a thread-like body, thicker at one end than at the other, and coiled spirally like a corkscrew. From the thin end two long cilia proceed; and, when the cells are burst, and the antherozooids are set free, they are propelled rapidly, with the small end forwards, by the vibration of the cilia. These antherozooids answer to the spermatozoa of animals, and represent the male element of the Chara. The sporangia or spore-fruits are borne upon short stalks, the end of which supports a large oval central cell; five spirally disposed sets of cells invest this, an aperture being left between the investing cells at the apex of the sporangium. When the antheridia attain maturity they burst, the anther- ozooids are set free, and swarm about in the water. Some of them enter the aperture of the sporangium, and, in all probability, pierce the free summit of the oval central cell, and enter its protoplasm; but all the steps of this process of impregnation have not been worked out. The result, however, is, that the contents of the central cell become full of starchy and oily matter; the spiral cells forming its coat acquire a dark colour and hard texture, and the sporangium, detaching itself, falls into the mud. After a time, it germinates; a tubular process, like a hypha, protrudes from its open end, and almost immediately gives off a branch, which .is the first root (compare the germination of the spore of a fern below). The hypha-like tube elongates, and becomes divided transversely into cells, the protoplasm of which developes chlorophyll. Very soon, the further growth of this pro-embryo is arrested. But one of the cells, which lies at some distance below the free end of the pro-embryo, undergoes budding, and gives rise to a set of leaves (which are not arranged in a whorl), amidst 46 ELEMENTARY BICLOGY. [vI. which a bud appears, which has the structure of the terminal bud of the adult Chara stem, and grows up into a new Chara. We have then, in Chara, a plant which is acrogenous (or grows at its summit), and which becomes segmented by the development of appendages, at intervals, along an axis; which multiplies, asexually by bulb-like buds, and also multi- plies sexually by means of the antherozooids (male elements) and central cells of the sporangia (female elements); in which the first product of the germination of the impregnated ovicell is a hypha-like body, from which the young Chara is developed by the gemmation and growth of one cell; so that there is a sort of alternation of generations, though the alternating forms are not absolutely distinct from one another. Chara flourishes in pond-water under the influence of sunlight, and by the aid of its chlorophyll, so that its nu- tritive processes must be the same as those of Protococcus, From its complete immersion, and the absence of any duct- like, or vascular tissues, it is probable that all parts absorb and assimilate the nutriment contained in the water; and that, except so far as the reproductive organs are concerned, there is a morphological differentiation of organs, unac- companied by a corresponding physiological differentiation. Mitella is a rarer plant than Chara, and is simpler in structure, its axis being devoid of the vertical layer. In other respects, however, it is very similar to Chara, and its structure is more easily made out. [The Characew, or plants belonging to the genera Chara and Nitella, are found in all parts of the world, and are in many respects closely allied to the Algce, or water-weeds. But no Algee are provided with an axis and appendages possessing a similar structure, or following the same law of growth, nor have any similar reproductive organs. The antherozooids of the Characee are, in fact, similar to those of the mosses, from which however the Characee differ widely in all other respects. ] vi] A. STONEWORTS. 47 LABORATORY WORK. NAKED-EYE CHARACTERS. Note the slender elongated axis (stem); the whorled appendages (leaves); the nodes and internodes ; the shortening of the latter towards the apex of the stem; the rhizoids. a. The roots; small; serving chiefly for attachment, the plant getting most of its nutrition, through other parts, from matters dissolved in the water. b. Lhe leaves; their sub-divisions (leaflets); their form, size, &e. c. The spore-fruits and antheridia; their position, size, form, colour. Draw a portion including two or three internodes. B. HISTOLOGICAL STRUCTURE, J 1S A) a. The stem. Examine the outside of a fresh internode with a low power, or a pocket-lens, to see the spirally arranged cortical cells. Hold a bit of fresh stem between two pieces of carrot, or imbed it in paraffin, and, with a sharp razor, cut thin transverse and longitudinal slices through uodes and internodes. Note the cavity of the large central cell (medullary or internodal cell) in the internodes; the cortical cells, set on obliquely round the medullary cell; the nodal cells, and the interruption of the central cavity at the nodes. Examine similar sections in specimens treated with spirit, and also preparations made by teasing or press- ing out in glycerine bits of stem from chromic-acid (0-2 per cent.) preparations: make out in these,— ELEMENTARY BIOLOGY. : [VI The nodal, internodal, and cortical cells. The wall (sac), protoplasmic layer (primordial utricle), nucleus, and vacuole of each cell. (The nucleus, is not always to be found in old cells.) Draw. Examine sections from the fresh stem to make out the points detailed in B.a. 3.8. The protoplasm and nucleus are difficult to see. Note the chlorophyll- granules. (See B. b. ¥.) Stain sections of the fresh stem with iodine, and magenta: note the results. b. The leaves. Examine fresh and chromic-acid specimens, a. B. The large uncovered terminal cell. Then a series of internodal cells, separated from one another and covered in by nodal cells: the sac, protoplasm, nucleus, and vacuole of each. The chlorophyll: collected into oval granules, and arranged so as to leave an oblique uncoloured band round each cell; the position of these granules in’ the more superficial layer of the protoplasm. The protoplasmic movements (see C. a.). The terminal bud. Dissect out chromic-acid specimens as far as pos- sible with needles, and then press gently out in glycerine. Note in different specimens— 71.] d. M. STONEWORTS. 49 a. The terminal or apical cell: a. Its form: hemispherical, the rounded surface free; the flat surface attached to the cell below it. B. Structure: sac, protoplasm, nucleus; no vacuole present. Sometimes two nuclei; preliminary to division. 8. Its mode of division; across the long axis of the stem, giving rise to two superimposed nucleated cells. b. The further fate of the new cells which are successively segmented off from the terminal cell; work back in your specimens from the terminal cell. a. The new cells are successively nodal and inter- nodal; the latter enlarge, develope a large vacuole, and ultimately form the medullary cells of the internodes; they never divide. 8B. The nodal cells divide freely, and do not increase much in size; they form the nodes, and the cortical cells. c. The development of leaves: by the multiplication and outgrowth of nodal cells. Their growth at the base, the terminal leaf-cell soon attaining its full size and not dividing. d. The development of branches; from nodal cells in leaf-axils, which take on the character of ter- minal cells. The spore-fruits. Examine fresh, under a low power. ELEMENTARY BIOLOGY. [v a. Made up externally of five twisted cells, bearin at their apices five smaller, not twisted cells, 8. Cut sections from imbedded specimens, an examine with a high power: make out th large central nucleated cell; the fatty an starchy matters contained in it; stain wit iodine. y. Press out chromic acid specimens in glycerine make out the above points (d. a. 8). 6. Examine chromic acid specimens for youn; spore-fruits, and press them out in glycerine make out in the youngest the five roundisl cells surrounding a central one; then in olde specimens the elongation, and twisting of th external cells, and the separation of their apice as five distinct cells. e. The Antheridia. a. Examine, with a low power, a ripe (orange coloured) one. a. Make out its external dentated cells. 8. Tease out a ripe antheridium in water; an examine with a high power; note the flat dentated, nucleated external cells; the cylin drical cell (manubrium) springing perpendicu larly from the inner surface of each; th roundish cell (capitulum) on the inner end o the manubrium; the six secondary capitul attached to the capitulum; the thread-lik filaments (usually four) proceeding from ead of the secondary capitula. vi] b. B. STONEWORTS. 51 The structure of these threads; each consists of a single row of cells, containing in unripe specimens nucleated protoplasm; in older spe- cimens each contains a coiled-up antherozooid. The antherozooids. Their form and structure; thickened at one end and granular; tapering off gradually to- wards the other end which is hyaline, and has two long cilia attached to it. The movements in water of ripe anthero- zovids. [Sometimes Chara cannot be obtained, when Nitella, another genus of the same natural order, and of similar habit and structure, can. Nearly all the points above described for Chara can be made out in Nitella, with the following differences: the cortical cells of the stem and leaves are absent, and, in the commoner species, the plant is not hardened by calcareous deposit; the branches arise, not one from a whorl of leaves, but two ; and the five twisted cells of the spore-fruit are each capped by two small cells, instead of one. ] C. PROTOPLASMIC MOVEMENTS IN VEGETABLE CELLS. a. Chara. Take a vigorous-looking fresh Chara or Nitella-cell (say the terminal cell of a leaf), and examine it in water with a high power. Note the superficial layer of protoplasm in which the chlorophyll lies; it is stationary: focus through this layer and examine the deeper one; note the currents in it, marked by the granules they carry along: their direction; in the long axis of the cell, up one side and down the other, the boundary of the two currents being marked 4—2 ‘B2 ELEMENTARY BIOLOGY. [ VI. by the colourless band, in which no movements occur. Try to find the nucleus; it has usually disappeared in cells in which currents have com- menced, but when present is passive and carried along by them. Sometimes it is very difficult, on account of the incrustation of the leaf-cells of Chara, to make out the protoplasmic movements in them; if this is found to be the case, the manubrial cells from an antheridium should be used instead. Tradescantia, Examine in water, with a high | power, the hairs which grow upon the stamens: they consist of a row of large roundish cells, each’ with sac, protoplasm, nucleus, and vacuolar spaces. Note the protoplasm; partly forming a layer (primordial utricle) lining the sac, and heaped up round the nucleus, and partly forming bridles running across the cell in yarious di- rections from the neighbourhood of the nucleus and from one part of the protoplasm to another; observe the currents in these bridles; from the nucleus in some, towards it in others. Vallisneria, Take a leaf beginning to look old; split it into two layers with a sharp knife and mount a bit in water; examine with a high power. Note the larger rectangular cells, be- longing to the deeper layers, with well-marked currents in them, which carry the chlorophyll granules round and round inside the cell-wall. If no currents are seen at first, gently warm the leaf by immersing it for a short time in water heated to a temperature between 30° and 35°C, vI.] d. STONEWORTS. 53 Anacharis. Take a yellowish-looking leaf: mount in water and examine with a high power; the phenomena observed are like those in Vallisneria. They are best observed in the single layer of cells at the margin of the leaf. Nettle-hair. Mount an uninjured hair in water with the bit of leaf to which it is attached (it is essential that the terminal recurved part of the large cell forming the hair be not broken off) ; examine with the highest available power ‘ currents carrying along very fine granules will be seen in the cell, their general direction hemg that of its long axis. VI. THE BRACKEN FERN (Péeris aquilina). THE conspicuous parts of this plant are the large green leaves, or fronds, which rise above the ground, sometimes to the height of five or six feet, and consist of a stem-like axis or rachis,from which transversely disposed offshoots proceed, these ultimately subdividing into flattened leaflets, the pinnules. The rachis of each frond may be followed for some distance into the ground. Its imbedded portion acquires a brown colour, and eventually passes into an irregularly branched body, also of a dark-brown colour, which is commonly called the root of the fern, but is, in reality, a creeping underground stem, or rhizome. From the surface of this, numerous fila- mentous true roots are given off. Traced in one direction from the attachment of the frond, the rhizome exhibits the withered bases of fronds, developed in former years, which have died down; while, in the opposite direction, it ends, sooner or later, by a rounded extremity beset with numerous fine hairs, which is the apex, or growing extremity, of the stem. Between the free end and the fully formed frond one or more processes, the rudiments of fronds, which will attain their full development in following years, are usually found. The attachments of the fronds are nodes, the spaces between two such successive attachments, internodes. It will be observed that the internodes do not become crowded vIt.] THE BRACKEN FERN, 55 towards the free end, and there is nothing comparable to the terminal bud of Chara with its numerous rudimentary appendages. When the fronds have attained their full size, the edges of the pinnules will be observed to be turned in towards the underside, and to be fringed with numerous hair-like pro- cesses which roof over the groove, inclosed by the incurved edge. At the bottom of the groove, brown granular bodies are aggregated, so as to form a streak along each side of the pinnule. The granules are the sporangia, and the streaks formed by their aggregation, the sort. Examined with a magnifying glass, each sporangium is seen to be pouch-shaped, like two watch-glasses united by a thick rim. When ripe, it has a brown colow,, readily bursts, and gives exit to a number of minute bodies which are the spores. ; The plant now described is made up of a multitude of cells, having the same morphological value as those of Chara, and each consisting of a protoplasmic mass, a nucleus and a cellulose wall. These cells, however, become very much modified in form and structure in different regions of the body of the plant, and give rise to groups of structures called tissues, in each of which the cells have undergone special modifications. These tissues are, to a certain extent, recog- nizable by the naked eye. Thus, a transverse section of the rhizome shews a circumferential zone of the same dark brown colour as the external epidermis, inclosing a white ground substance, interrupted by variously disposed bands, patches, and dots, some of which are of the same dark-brown hue as the external zone, while others are of a pale yellowish-brown. The dark brown dots are scattered irregularly, but the major part of the dark brown colour is gathered into two narrow bands, which lie midway between the centre and the circumference. Sometimes the ends of these bands are 56 ELEMENTARY BIOLOGY. [vu. united. Inclosed between these narrow, dark-brown bands are, usually, two elongated, oval, yellowish-brown bands;' and outside them, lie a number of similarly coloured patches, one of which is usually considerably longer than the others, A longitudinal section shews that each of these patches of colour answers to the transverse section of a band of similar substance, which extends throughout the whole length of the stem; sometimes remaining distinct, sometimes giving off branches which run into adjacent bands, and sometimes uniting altogether with them. At a short distance below the apex of the stem, however, the colour of all the bands fades away, and they are traceable into mere streaks, which finally disappear altogether in the semi-transparent gelatinous substance which forms the grow- ing end of the stem. Submitted to microscopic examination, the white ground substance, or parenchyma, is seen to consist of large polygonal cells, containing numerous starch granules; and the circumferential zone is formed of somewhat elongated cells, the thick walls of which have acquired a dark-brown colour, and contain little or no starch. The dark-brown bands, on the other hand, consist of cells which are so much elongated as almost to deserve the name of fibres and constitute what is termed sclerenchyma. Their walls are very thick, and of a deep-brown colour; but the thickening has taken place unequally, so as to leave short, obliquely directed, thin places, which look like clefts. The yellow bands, lastly, are vascular bundles. Each consists, externally, of thick-walled, elongated, parallel-sided cells, internal to which lie elongated tubes devoid of protoplasm, and frequently containing air. In the majority of these tubes, and in all the widest, the walls are greatly thickened, the thickening having taken place along equidistant transverse lines. The tubes have become flat- tened against one another, by mutual pressure, so that they are five- or six-sided; and, as the markings of their flattened vit.] THE BRACKEN FERN, 57 walls simulate the rounds of a ladder, they have been termed scalariform ducts or vessels. The cavities of these scalariform ducts are divided at intervals, in correspondence with the lengths of the cells of which they are made up, by oblique, often perforated, partitions. Among the smaller vessels, a few will be found, in which the thickening forms a closely wound spiral. These are spiral vessels. The rachis of a frond, so far as it projects above the surface of the ground, is of a bright green colour; and, in transverse section, it presents a green ground-substance, inter- rupted by irregular paler markings, which are the transverse sections of longitudinal bands of a similar colour. There are no brown spots or bands. Examined microscopically, the ground-substance is found to be composed of polygonal cells containing chlorophyll. These are invested superficially by an epidermis, composed of elongated cells, with walls thick- ened in such a manner as to leave thin circular spots here and there. Hence, those walls of the cells, which are at right angles to the axis of vision, appear dotted with clear spots; while, in those walls of which transverse sections are visible, the dots are seen to be funnel-shaped depressions. The pale bands are vascular bundles containing scalari- form and spiral vessels. The outer layer investing each is chiefly formed of long hollow fibres with very thick walls, and terminating in a point at each end. These scleren- chymatous fibres have oblique cleft-like clear spaces, pro- duced by interruptions of the process of thickening in their walls. The vascular bundles, the green parenchyma, and the epidermis are continued into each pinnule of the frond. The epidermis retains its ordinary character on the upper side of the pinnule, except that the contours of its component cells become somewhat more irregular. On the under side, many hairs are developed from it, and the cells become ns ELEMENTARY BLOLOGY, [var sthetlarly moditied tn form, their walls being thrown oul tnto lobes, whieh interlock with Chose of adjacent cells, Between many of these cells an oval space is lefl, forming a channel of commetniention between the titerior of the frond and the exterior, ‘Phe opening of this space is) sar mounted by two rentform cells, the coneavittes of whieh are darned towards one another, while them ends are in coutaek "Phe opening tefl between the appled concave fees is ak sfomate; and, as the sfomefes are present in Immense timbers, there is a free commatiniention between the outer air and the dafercedfadar passages which exist in the substunee of the frond. Phase cells af the green parenchyma of the frond whieh form the iaferior half of its thickness, tn thet, are irregularly elongated, and) frequently produced: inte several processes, or stellate, Mhey come into contieh with adjacent: cells only by comparatively small parts oof there stafaces, or by ¢ho ends of these processes, They hus bound) passaees between the eells, difercedlutay passages, Which are fulboof air, and are in commitntention with stiihay bat narrower, passaeves, which extend through- out Che substunce of the plant, The vascular bundles break up in the pinnules, and follow the course of the so ealled vevus which are. visible Upon Tis surties ; duets being continued: dato their ultimate ramifien tions, The rootlets prosent an outer coat of epidermis, enclosing petrenehy nia traversed by ac eentral vascular bundle. ‘They Increase Ta leneth by the division and subdivision of) the eolls at the growing point, bub this point is not situated ab the very stefiee of the rootlet, as the growing poiut at the evCremity of the rhizome is, butois covered hy a eap of eels. When the spores ave sown tpen danip earth, ora tile, or aslip of vhiss, and hop Choroughty moist and warm, they germinate, Hach gives rise Con tubular, hy phaclike, prolongs. VIL] THE BRACKEN FERN. 59 tion, which developes a similar process, the primitive rootlet, close to the spore. The hypha-like prolongation, at first, undergoes transverse division, so that it becomes converted into a series of cells. Then, the cells at its free end divide longitudinally, as well as transversely, and thus give rise to a flat expansion, which gradually assumes a bilobed form, and becomes thickened, in some parts, by division of its cells in a direction perpendicular to its surface. The protoplasm of these cells developes chlorophyll granules, whereby the bilobed disk acquires a green colour; while numerous simple radicle fibres are given off from its under surface, and attach the little plant, which is termed a prothallus or prothallium, to the surface on which it grows. The prothallus attains no higher development than this, and does not directly grow into a fern such as that in which the spores took their origin; but, after a time, rounded or ovoidal elevations are developed, by the outgrowth and division of the cells which form its under aspect. Some of these are antheridia. The protoplasm of each of the cells contained in their interior is converted into an antherozooid, somewhat similar to that of Chara, but provided with many more cilia. The antheridium bursts, and the antherozooids, set free from their containing cells, are propelled through the moisture on the under surface of the prothallus by their cilia. The processes of the second kind acquire a more cylin- drical form, and are called archegonia. Of the cells which are situated in the axis of the cylinder, all disappear but that which lies at the bottom of its cavity. This is the embryo cell, and when the archegonium is fully formed, a canal leads from its summit to this cell. The antherozooids enter by this canal, and impregnate the embryo cell. The embryo cell now begins to divide, and becomes converted into four cells; of these, the two which lie at the deepest part of the cavity of the archegonium subdivide and 60 ELEMENTARY BIOLOGY. [ VII. ultimately form a plug-like, cellular, mass, which imbeds itself firmly in the substance of the prothallus. Of the remaining two cells, which also undergo subdivision, one gives rise to the rhizome of the young fern, while the other becomes its first rootlet. It appears probable that the plug-like mass absorbs nutritive matter from the prothallus, and supplies the rhizome of the young fern, until it is able to provide for itself. As the rhizome grows, and developes its fronds, it rapidly attains a size vastly superior to that of the prothallus, which at length ceases to have any functional importance, and dis- appears. Thus Pterts presents a remarkable case of the alternation of generations. The large and complicated organism com- monly known as the “Fern” is the product of the impreg- nation of the embryo cell by the antherozooid. This “ Fern,” when it attains its adult condition, developes sporangia; and the inner cells of these sporangia give rise, by a perfectly asexual fissive process, to the spores. The spores when set free germinate; the product of that germination is the incon- spicuous and simply cellular prothallus; an independent organism, which nourishes itself and grows, and on which, eventually, the essential organs of the sexual process—the archegonia and antheridia—are developed. Each impregnated embryo cell produces only a single “fern,” but each “fern” may give rise to innumerable pro- thallia, seeing that every one of the numerous spores de- veloped in the immense multitude of sporangia to which the frond gives rise, may germinate. Vit.] THE BRACKEN FERN. 61. LABORATORY WORK. A. THE FERN-PLANT ; ASEXUAL GENERATION, a, External characters. a. The brown underground stem or rhizome: its nodes and internodes, b. The roots springing from the rhizome. c. The leaves or fronds arising from the rhizome at intervals. a. The great amount of subdivision of the frond: its main axis (rachis) ; the primary divisions or pinne ; the ultimate divisions or pinnules. 8. The sori; small brown patches along the mar- gin of the under surface of some of the pin- nules, d, The nodes and internodes of the rhizome. The absence of a terminal bud on it. b. The rhizome. 1. Cut it across and draw the section as seen with the naked eye. a. The outer brownish layer (epidermis and sub- epidermis.) b. The yellowish-white substance (parenchyma) form- ing most of the thickness of the section. c. The internal incomplete brown ring (sclerenchyma) imbedded in the parenchyma. d. The small patches of sclerenchyma scattered about in the parenchyma outside the main sclerenchymatous ring. 1o é. ELEMENTARY BIOLOGY. [VII The yellowish tissue (vascular bundles) lying inside and outside the ring of sclerenchyma. Cut a longitudinal section of the rhizome: make out on the cut surface b. 1. a. bc. Cut a thin transverse section of the rhizome, mount in water and examine with 1 inch obj. a dd. The single layer of much thickened epidermic cells. The small opaque angular contours of the sub- epidermie cells (external sclerenchyma). The large polyhedral more transparent paren- chymatous cells. The small opaque angular contours of the cells of the internal sclerenchyma, The great openings of the ducts and vessels in the fibro-vascular bundles. Draw the section. Examine with } obj. a. b. a. The epidermis : its thick-walled cells. The parenchyma : its large thin-walled cells: their sac, protoplasm and nucleus: the great number of starch granules in them. The various patches of sclerenchyma, made up of thick-walled angular cells. The vascular bundles. Note in each:— Outside, a single layer of cells containing no starch-granules (sheath-cells). vit] or é. THE BRACKEN FERN. 63 Within the sheath-cells a layer of small paren- chymatous cells containing starch. Within the last layer come the bast-cells ; small rectangular cells with slightly thickened walls, and arranged in several rows. Within the bast layer, come one or more rows of larger thin-walled cells, The cross sections of the vessels: their greatly thickened walls, and large central cavity con- taining no protoplasm. Scattered here and there, in the spaces between the angles of the vessels, are small parenchyma- tous cells containing starch-granules. Treat with iodine: the protoplasm stained brown ; the starch-granules deep blue, rendering some of the cells quite opaque and almost black-looking. Cut a thin longitudinal section of the stem and examine with 1 inch and then with $ obj. Make out the various tissues described in 3 and 4. a. The epidermis and parenchyma, much as in the transverse section. The sclerenchyma is seen to be made up of greatly elongated cells, tapering towards each end. The vascular bundles ; note in them— The sheath-cells and parenchyma much as in the transverse section. The vessels: elongated tubes presenting cross partitions at long intervals. Two forms of vessel will be seen, viz. scalariform vessels, ELEMENTARY BIOLOGY. {vir with regular transverse thickenings on their walls and spiral vessels, less numerous than the last form: with a continuous spiral thickening on their walls. y. The bast-cells: seven or eight times as long as they are broad, and terminating obliquely at each end. 6. The elongated larger cells (4. d. 6.): they have very slightly thickened walls and no scalariform markings. [Cut off half an inch of the growing end of the stem, imbed it in paraffin upside down, and cut a series of transverse sections: examine them with the microscope, beginning with those farthest from the growing point. At first the various tissues described in 3 and 4 will be readily recognisable ; as the sections nearer the growing point are examined they will be less distinct, and close to the growing point the whole section will be found to be composed entirely of parenchymatous closely fitting cells.] [c. The leaf. Imbed a leaf in paraffin and cut a thin vertical section: examine with 1 inch obj. It will be found to be constructed essentially on the same plan as the leaf of the bean. (VIIT.)] d. The reproductive organs. Examine a sorus with 1 inch obj. without a cover-glass. It is composed of a great number of minute oval bodies, the sporangia. Scrape off some sporangia and mount in water: ex- amine with 1 inch obj. a. Their form: they are oval biconvex bodies borne on a short stalk. 11] THE BRACKEN FERN. 65 b. Their structure: composed of brownish cells, one row of which has very thick walls, and forms a marked ring (annulus) round the edge of the sporange. c. Their mode of dehiscence (look out for one that has opened): by a cleft running towards the centre of the sporange from a point where the annulus has torn across. 8. Burst open some sporangia by pressing on the cover- glass: examine with } obj. the spores which are set free. a. Thetr size: measure. b. Their form: somewhat triangular. [c. Lhetr structure ; a thick outer coat, a thin inner coat, protoplasm, and a nucleus: crush some by pressure on the cover-glass. | 3. THE PROTHALLUS; SEXUAL GENERATION. Prothalli may be obtained by sowing some spores on a lass slide, and keeping them warm and very moist for about hree months. They are small deep green leaf-like bodies, a. The Prothallus. 1. Transfer a prothallus to a slide, and mount it in water with its under surface uppermost. Examine with 1 inch obj. a. Its form: a thin kidney-shaped expansion from which, especially towards its convex border, a number of slender filaments (rootlets) arise. b. Its structure. a. The leafy expansion: it consists throughout most of its extent of a single layer of. polyhe- 5 66 i; ELEMENTARY BIOLOGY. [vir dral chlorophyll-containing cells, but at parts it is more than one cell thick. B. The rootlets: composed of a series of cells which contain no chlorophyll. The antheridia and archegonia: these can just be seen with an inch objective as minute eminences on the under surface of those parts of the prothallus which consist of several layers of cells. b. The reproductive organs. These are to be found by examining the under surface of the prothallus with $ obj. The antheridia. Most numerous near and among the rootlets. a. b. Their form: small hemispherical eminences. Their structure: made wp of an outer layer of cells containing a few chlorophyll-granules and through which can be seen a number of smaller cells which occupy the centre of the organ: in the latter cells, in ripe antheridia, spirally coiled bodies (antherozooids) can be indistinctly seen. The antherozooids. Some of these are sure to be found swimming about in the water if a number of ripe prothalli are examined. a. Small bodies, coiled like a corkscrew, thick at one end, and tapering towards the other, which has a number of cilia attached to it. To the thicker end of the antherozooid is often attached a rounded mass containing colourless granules. Treat with iodine; this stains them and stops THE BRACKEN FERN. 67 their movements so that their form can be more distinctly seen. 3. The archegonia. Most numerous towards the concave border of the prothallus. a Their form: chimney-shaped eminences with a small aperture at the apex. Their structure: composed of a layer of trans- parent cells, containing no chlorophyll, arranged in four rows, and surrounding a central cavity which extends into the cushion formed by the thickened part of the prothallus (a. 1. 6. a), In this cavity lies, in young specimens, a large nucleated granular basal cell, with two or three smaller granular cells above it in the narrow upper part of the cavity; in older specimens this upper part is empty, forming a canal leading down to the basal cell. 4, Examine young Fern in connexion with its prothallus. VIII. THE BEAN-PLANT. (Vicia faba.) In this, which is selected as a convenient example of a Flowering Plant, the same parts are to be distinguished as in the Fern; but the axis is erect and consists of a root imbedded in the earth and a stem which rises into the air. The appendages of the stem are leaves, developed from the op- posite sides of successive nodes; and the internodes become shorter and shorter towards the summit of the stem, which ends in a terminal bud. Buds are also developed in the axils of the leaves, and some of them grow into branches, which repeat the characters of the stem; but others, when the plant attains its full development, grow into stalks which support the flowers; each of which consists of a calyx, a corolla, a staminal tube and a central prstil; the latter is terminated by a style, the free end of which is the stigma. The staminal tube ends in ten filaments, four of which are rather shorter than the rest; and the filaments bear oval bodies, the anthers, which, when ripe, give exit to a fine powder, made up of minute pollen grains. The pistil is hollow ; and, attached by short stalks along the ventral side of it, or that turned towards the axis, is a longitudinal series of minute bodies, the ovules. Each ovule consists of a central conical nucleus, invested by two coats, an outer and an inner. Opposite the summit of the nucleus, these coats are per- furated by a canal, the micropyle, which leads down to the I] THE BEAN-PLANT, 69 icleus. The nucleus contains a sac, the embryo sac, in hich certain cells, one of which is the embryo cell, and ie rest endosperm cells, are developed. A pollen grain »posited on the stigma, sends out a hypha-like prolongation, ie pollen tube, which elongates, passes down the style, and ventually reaches the micropyle of an ovule. Traversing 1e micropyle, the end of the pollen tube penetrates the ucleus, and comes into close contact with the embryo sac. ‘his is the process of impregnation, and the result of it ; that the embryo cell divides and gives rise to a cellular mbryo. This becomes a minute Bean-plant, consisting of a adicle or primary root; of two, relatively large, primary saves, the cotyledons; and of a short stem, the plumule, on ‘hich rudimentary leaves soon appear. The cotyledons now aerease in size, out of all proportion to the rest of the em- ryonic plant; and the cells of which they are composed be- ome filled with starch and other nutritious matter. The ucleus and coats of the ovule grow to accommodate the en- arging embryo, but, at the same time, become merged into an nvelope which constitutes the coat of the seed. The pistil nlarges and becomes the pod; this, when it has attained its ull size, dries and readily bursts along its edges, or decays, etting the seeds free. Each seed, when placed in proper con- litions of warmth and moisture, then germinates. The cotyle- lons of the contained embryo swell, burst the seed coat, and, yecoming green, emerge as the fleshy seed leaves. The nutri- jous matters which they contain are absorbed by the plumule ind radicle, the latter of which descends into the earth and secomes the root, while the former ascends and becomes the stem of the young bean-plant. The apex of the stem retains, chroughout life, the simply cellular structure which is, at Grst, characteristic of the whole embryo; and the growth n length of the stem, so far as it depends on the addition of aew cells, takes place chiefly, if not exclusively, in this part. 70 ELEMENTARY BIOLOGY. [vi The apex of the root, on the other hand, gives rise to a root-sheath, as in the Fern. The leaves cease to grow by cell multiplication at their apices, when these are once formed, the addition of new cells taking place at their bases. The tissues which compose the body of the Bean-plant are similar, in their general characters, to those found in the Fern, but they differ in the manner of their arrangement. The surface is bounded by a layer of epidermic cells, within which, rounded or polygonal cells make up the ground- substance, or parenchyma, of the plant, extending to its very centre in the younger parts of the stem and in the root; while, in the older parts of the stem, the centre is occupied by a more or less considerable cavity, full of air. This cavity results from the central parenchyma becoming torn asunder, after it has ceased to grow, by the enlargement of the peripheral parts of the stem. Nearer to the circumference than to the centre, lies a ring of woody and vascular tissue, which, in transverse sections, is seen to be broken up into wedge-shaped bundles, by narrow bands of parenchymatous tissue, which extend from the parenchyma within the circle of woody and vascular tissue (medulla or pith) to that which lies outside it. Moreover each bundle of woody and vascular tissue is divided into two parts, an outer and an inner, by a thin layer of small and very thin-walled cells, termed the cambium layer. What lies outside this layer belongs to the bark and epidermis ; what lies inside it, to the wood and pith. The great morphological distinction between the axis of the Bean and that of the Fern lies in the presence of this cambium layer. ~The cells composing it, in fact, retain their power of multiplication, and divide by septa parallel with the length of the stem, or root, as well as transverse to it. Thus new cells are continually being added, on the inner side 711.] THE BEAN-PLANT. aL f the cambium layer, to the thickness of the wood, and on the outer side of it, to the thickness of the bark; and the wis of the plant continually increases in diameter, so long as , ihis process goes on. Plants in which this constant addition io the outer face of the wood and the inner face of the bark iakes place, are termed exogens. At the apex of the stem, and at that of the root, the sambium layer is continuous with the cells which retain ihe capacity of dividing in these localities. As the plant is chickest at the junction of the stem and root, and diminishes ihence to the free ends, or apices, of these two structures, ihe cambium layer may be said to have the form of a double cone. And it is the special peculiarity of an exogen to possess this doubly conical layer of constantly dividing cells, the upper md of which is free, at the growing point of the terminal yud of the stem, while its lower end is covered by the root- ‘ap of the ultimate termination of the principal root. The most characteristic tissues of the wood are dotted lucts and spiral vessels, the spiral vessels being particularly vbundant close to the pith. The bark contains elongated aber or bast cells; but there are no scalariform vessels such is are found in the Fern. Stomates are absent in the epidermis of the root: they we to be found, here and there, in the epidermis of all the rreen parts of the stem and its appendages, but, as in the Tern, they are most abundant in the epidermis of the under ide of the leaves. As in the Fern, they communicate with ntercellular passages, which are widest in the leaves, but ‘xtend thence throughout the whole plant. The difference between a flowering plant, such as the 3ean, and a flowerless plant, such as the Fern, at first sight \ppears very striking, but it has been proved that the two are yut the extreme terms of one series of modifications. The 72 ELEMENTARY BIOLOGY. [vio anther, for example, is strictly comparable to a sporangium. The pollen grains answer to the male spores of those flower- less plants in which the spores are of distinct sexes—some spores giving rise to prothallia which develope only anthe- ridia, and others to prothallia which develope only arche- gonia; instead of the same prothallia producing the organs of both sexes, as in Pteris. And the pollen tube corresponds with the first hypha-leke process of the spore. But, in the flowering plants, the protoplasm of the pollen tube does not undergo division and conversion into a prothallus, from which antheridia are developed, giving rise to detached fertilizing bodies or antherozooids, but exerts its fertilizing influence without any such previous differentiation. The connecting links between these two extreme modifications are furnished, on the one hand, by the Conifers, in which the protoplasm of the pollen tube becomes divided into cells, from which, however, no antherozooids are developed; and the Club- mosses, in which the protoplasm of the male spores (= pollen grains) divides into cells which form no prothallus, but give rise directly to antherozooids. On the other hand, the embryo sac is the equivalent of a female spore: the endosperm cells, which are produced from part of its protoplasm, answer to the cells of a prothallus; while the embryo cell of the flowering plant corresponds with the embryo cell contained in the archegonium of the prothallus. In the development of the female spore of the flowering plant, therefore, the free prothallus and the arche- gonia are suppressed. Here again, the intermediate stages are presented by, the Conifers and the Club-mosses. For, in the Conifers, the protoplasm of the embryo sac gives rise to a solid prothallus-like endosperm, in which bodies called corpuscula, which answer to the archegonia, are formed; and in these the embryo cells arise; while, in some of the Club-mosses, there are female spores distinct from the male VII] THE BEAN-PLANT. 73 spores, and the prothallus which they develope does not leave the cavity of the spore, but remains in it like an endosperm. The physiological processes which go on in the higher green plants, such as the Fern and the Bean, resemble, in the gross, those which take place in Protococcus and Chara. For such plants grow and flourish if their roots are im- mersed in water containing a due proportion of certain saline matters, while their stem and leaves are exposed to the air, and receive the influence of the sun’s rays. A Bean-plant, for instance, may be grown, if supplied through its roots with a dilute watery solution of potassium and calcium nitrate, potassium and iron sulphate, and mag- nesium sulphate. While growing, it absorbs the solution, the greater part of the water of which evaporates from the ex- tensive surface of the plant. In sunshine, it rapidly decom- poses carbonic anhydride, fixing the carbon, and setting free the oxygen; at night, it slowly absorbs oxygen, and gives off carbonic acid; and it manufactures a large quantity of pro- tein compounds, cellulose, starch, sugar and the like, from the raw materials supplied to it. It is further clear that, as the decomposition of carbonic anhydride can take place only under the combined influences of chlorophyll and sunlight, that operation must be con- fined, in all ordinary plants, to the tissue immediately be- neath the epidermis in the stem, and to the leaves. And it can be proved, experimentally, that fresh green leaves possess this power to a remarkable extent. On the other hand, it is clear that, when a plant is grown under the conditions described, the nitrogenous and mineral sonstituents of its food can reach the leaves only by passing from the roots, where they are absorbed, through the stem to the leaves. And, at whatever parts of the plant the nitro- 74 ELEMENTARY BIOLOGY. [VvIIL, genous and mineral constituents derived from the roots are combined with the carbon fixed in the leaves, the resulting compound must be diffused thence, in order to reach the deep-seated cells, such for instance as those of the cambium layer and those of the roots, which are growing and multi- plying, and yet have no power of extracting carbon directly from carbonic anhydride. In fact, those cells which contain no chlorophyll, and are out of the reach of light, must live after the fashion of Toruda; and manufacture their protein out of a material which contains nitrogen and hydrogen, with oxygen and carbon, in some other shape than that of carbonic anhydride. The analogy of Torula suggests a fluid which contains in solution, either some ammoniacal salt com- parable to ammonium tartrate, or a more complex compound analogous to pepsin. Thus, the higher plant combines within itself the two, physiologically distinct, lower types of the Fungus and the Alga. That some sort of circulation of fluids must take place in the body of a plant, therefore, appears to be certain, but the details of the process are by no means clear. There is evidence to shew that the ascent of fluid from the root to the leaves takes place, to a great extent, through the elon- gated ducts of the wood, which not unfrequently open into one another by their applied ends, and, in that way, form very fine capillary tubes of considerable length. The mechanism by which this ascent is effected is of two kinds; there is a pull from above, and there is a push from below. The pull from above is the evaporation which takes place at the surface of the plant, and especially in the air passages of the leaves, where the thin-walled cells of the parenchyma are surrounded, on almost all sides, with air, which communicates directly with the atmosphere through the stomates. The push from below is the absorptive action which takes place at the extremities of the rootlets, and vit. ] THE BEAN-PLANT, 75 which, for example, in a vine, before its leaves have grown in the spring, causes a rapid ascent of fluid (sap) absorbed from the soil. A certain portion of the fluid thus pumped | up from the roots to the surface of the plant doubtless exudes, laterally, through the walls of the vessels (the thin places which give rise to the dots on the walls of these structures, especially favouring this process), and, passing from cell to cell, eventually reaches those which contain chlorophyll. The distribution of the compound containing nitrogen and carbon, whatever it may be, which is formed in the chlorophyll-bearing cells, probably takes place by slow diffusion from cell to cell. The supply of air, containing carbonic anhydride, to the leaves and bark is effected by the abundant and large air passages which exist between the cells in those regions. But it can hardly be doubted that all the living protoplasm of the plant undergoes slow oxidation, with evolution of carbonic anhydride; and that this process, alone, takes place in the deeper seated cells. The supply of oxygen needful for this purpose is sufficiently provided for, on the one hand, by the minute air passages which are to be found between the cells in all parenchymatous tissues; and on the other, by the spiral vessels, which appear always to contain air under normal circumstances, in the woody bundles. The replace- ment of the oxygen of the air thus absorbed, and the removal of the carbonic anhydride formed, will be sufficiently provided for by gaseous diffusion. From what has been said, it results that, in an ordinary plant, growing in damp earth and exposed to the sunshine, a current of fluid is setting from the root towards the surface exposed to the air, where its watery part is for the most part evaporated; while gaseous diffusion takes place, in the contrary direction, from the surface exposed to the air, through the air passages and spiral vessels which extend 76 ELEMENTARY BIOLOGY. [vir from the stomates to the radicles; the balance of exchange being in favour of oxygen, in all the chlorophyll-bearing parts of the plant which are reached by the sunlight, and in favour of carbonic anhydride, in its colourless and hidden regions. At night, the evaporation diminishing with the lowering of the temperature, the ascent of liquid becomes . very slow, or stops, and the balance of exchange in the air passages is entirely in favour of carbonic anhydride; even the chlorophyll-bearing parts oxydizing, while no carbonic anhydride is decomposed. LABORATORY WORK. a. General characters. a. The erect central main axis (root and stem). The branches : some, mere repetitions of the main axis; others, modified and bearing flowers. The nodes and internodes. d. The appendages. a. Rootlets. 8. Foliage leaves. y. Floral leaves. b. The root. a. Its main central portion (axis). b. The irregularly arranged rootlets attached to the axis. c. The absence of chlorophyll in the root. voit] Cc. THE BEAN-PLANT. 77 The root-sheath, covering the tip of each rootlet: this is difficult to get whole out of the ground in the bean, but is readily seen by examining the roots of duckweed (Lemna) with 1 inch obj. In the latter plant it consists of several layers of cells forming a cap on the end of the root, and ending abruptly with a prominent rim some way up it. The stem. Erect, green, four-cornered with a ridge at each angle ; not woody; the gradual shortening of the internodes towards its apex. Cut a thin transverse section of the stem, through an internode ; note its central cavity, and the whitish ring of fibro-vascular bundles in it, which is harder to cut than the rest: mount in water and examine with 1 inch obj.: note— a. The medullary or pith-cavity in the centre of the section. The pith-cells, around the central cavity: large and more or less rounded (parenchyma) : some- times with dotted walls from spots of local thin- ness on them. The epidermis: composed of a single layer of somewhat squarish-looking cells, containing no chlorophyll. Beneath the epidermis several layers of large rounded cells containing chlorophyll (parenchyma of the bark). The medullary rays: radiating rows of paren- chymatous cells uniting 6 and d: not quite con- 78 ELEMENTARY BIOLOGY. [viIt, tinuous, being interrupted by the cambiwm zone (Ff ¥)- The fibro-vascular bundles, lying between the medullary rays; commencing at the side nearest the pith, note— The large openings formed by the transverse sections of the spiral vessels and ducts. The small thick-walled wood-cells, wedged in between the vessels. The cambium zone; granular-looking, and composed of small angular thin-walled cells. The kber-layer: in cross section it seems composed of rounded cells with much thickened walls. Draw the section. Cut a transverse section through a node, and compare it with that through the internode. Cut a thin longitudinal section through part of an internode (if necessary the bit of stem may be im- bedded in paraffin first), and mount it in water; working from the medullary cavity outwards, note the following layers, using at first a low power. a. The pith-cells: much as in the transverse sec- tion. The spiral vessels: elongated tubes with a spiral thickening on their walls. The wood-cells: elongated and with much thick- ened walls. The dotted ducts: much like b, but the thickening not deposited in the form of a spiral. 7III.] THE BEAN-PLANT. 79 e. The cambium zone: made up of cloudy-looking, small, angular, thin-walled cells. f Laber-cells: fusiform and thick-walled. g. More parenchymatous cells: containing chloro- phyll. h. Epidermis: composed apparently of cubical colourless cells: here and there the opening of a stomate (d. 4. 8.) may be seen, Draw the section. 5. Compare the transverse and longitudinal sections together, making out the corresponding parts in each. 6. Put on a high power, and examine each of the above- mentioned tissues carefully. 7. Stain with iodine: note the cell-walls ; the protoplasm —its presence or absence, and relative quantity in the various tissues; the sweler of the cells; starch- granules in some, stained deep blue by the iodine. d. The leaves. 1. Their form and composition. a. Each leaf consists of a number of different parts, VIZ.-— a. The stalk or petiole. The four to six oval leaflets attached laterally to the stalk. y. The pair of small leaf-like expansions (stipules) at the base of the petiole, §. The rudimentary tendril terminating the pe- tiole, 80 ELEMENTARY BIOLOGY. [ VIII. 2. The histological structure of a leaflet. 6 a. C. g, Imbed a leaflet in paraffin or hold it hetween two bits of carrot or turnip and cut a thin section from it, perpendicular to its surfaces. Let the section lie in water a few minutes to drive the air out of its intercellular spaces, and then mount it in water, and examine with 1 inch objective. Begin at the upper surface (marked out by its more closely packed cells), and work through to the lower. Note— The colourless epidermic layer—consisting of a single row of cells; the openings here and there in it (stomata). Beneath the upper epidermis come elongated chlorophyll-containing cells, set on perpendicu- larly to the surface. Then come irregularly branched (stellate) cells forming the lower half of the leaf-substance; these also contain chlorophyll. The epidermic layer of the lower surface; like a. The intercellular spaces, through the whole thickness of the leaf: the direct communication of some of them with stomata. Here and there sections of ribs or veins : make out in them the same elements as in c. 2. f, Draw. Treat with iodine: make out the sac, proto- plasm (primordial utricle), nucleus and vacuole of the cells: the starch-granules. 11] THE BEAN-PLANT. 81 d. Peel off a strip of epidermis from a leaf and ex- amine with a low power: note— The large close-fitting cells, with irregularly wavy margins and no chlorophyll, which chiefly make up the epidermis. The openings here and there in it (stomata) ; the two curved, chlorophyll-containing cells bounding each stomate. Gently pull a midrib in two across its long axis; note the fine threads uniting the two broken ends; cut them off with a sharp pair of scissors, mount in water and examine with 4 or 4 ob- jective: they will be found to consist of partially unrolled spiral vessels. e. The flower. 1. Its general structure. a. Borne on a short stalk (peduncle). b. Composed of four rows or whorls of organs. a. B. ty. é The external green cup-like calya. Inside the calyx the corolla: the most con- spicuous part of the flower. Inside the corolla the stamens. Within the stamens the pistil. 2. The calyx. A cup terminated at its free edge by five prominent points, two dorsal, and three ventral: the five small midribs running along it (one to the end of each of the points) represent the free ends of five sepals, which are united below, 6 82. ELEMENTARY BIOLOGY. [vin 3. The corolla. a Y Composed of five pieces or petals. On the dorsal side, a single large piece (veail- lum) expanded at its free end and folded over the rest. On the sides, two oval pieces (the alc), each attached by a distinct narrowed stalk (unguis), The inferior part of the corolla (carina), com- posed of two oval pieces united along their lower edge but readily tearing apart. 4. The stamens. a. Ten in number, each consisting of a stalk-like part, the filament, terminated by a small knob, the anther. The union of the filaments for three-fourths of their length to form the stamen-tube: the. sharp bend of the filaments towards the upper side at the point where they separate from one another, Tease out an anther in water and examine with 4 obj.: there will be found numerous— Pollen-grains: small oval bodies, with pro- jections on them in the equatorial region. The anther of a bean is so small that sections cannot be made of it without considerable skill: the structure of an anther can however be easily made out by imbedding one from a tiger-lily in paraffin or holding it between two bits of carrot, cntting transverse sections, mounting in: water and examining with 1 inch obj. THE BEAN-PLANT. 83 It contains four chambers, two on each side of the continuation of the filament, and in each chamber lie numerous pollen-grains. 5. The pistil. a. It is found by tearing open the stamen-tube: it is a long green tapering body, somewhat flattened laterally and ending in a point (the style) which bears a tuft of strong hairs. Slit it open carefully: in it lies a central cavity, containing a number of small oval bodies, the ovules, attached along its ventral side by short pedicles. It is difficult to get a section of a bean-ovule, but its essential structure may be readily made out by making thin transverse sections of the ovary of a large lily (where the ovules are closely im- bedded in a large quantity of parenchyma) and examining with 1 inch obj. The central cellular portion of the ovule (nucleus) made up of a large number of cells, Its two coats, an inner (primine) and outer (secundine). The small passage (micropyle) leading through the coats down to the nucleus. In some specimens, a large cavity (the embryo- sac) will be seen in the nucleus just opposite the micropyle. In the embryo-sac may be seen some small granular cells (the embryo- cell and endosperm cells). 6—2 84 ELEMENTARY BIOLOGY. [viit. f. The seeds. Soak some dried beans in water for twenty-four hours ; they will slightly swell up and be more readily ex- amined than when dry. a. Note the black patch on one end of the bean, ' marking where the stalk (funiculus) which fixed it in the pod was attached to it. b. Having wiped all moisture off the bean gently press it while observing that part of the black patch which is next its broader end: close to the patch a minute drop of fluid will be observed to be pressed out through a small opening, the micropyle. c. Carefully peel off the outer coat (testa) of the seed: the two large fleshy cotyledons will be laid bare. d. Joining the cotyledons together will be found the rest of the embryo: it consists of a conical part (the radicle) lying outside the cotyledons, with its apex directed towards the point where the micropyle was; and of the rudiments of the stem and leaves (plumule) lying between the cotyledons. g. The process of fertilization. This is difficult to follow in the bean; but by using different plants for the observation of its various stages it is fairly easy to observe all its more important steps. 1. A plant well adapted for seeing the penetration of the pollen-tube into the stigma and style is the Evening Primrose (@nothera biennis). Detach the style from the flower and hold the club- _ Shaped stigma between the finger and thumb of the TIL] 1 THE BEAN-PLANT. 85 left hand. Moisten it with a drop of water and then make with a wetted razor several successive cuts through it. This will divide the stigma into several slices. Spread these out on a glass slide with a needle in water and examine the thinnest, after put- ting on a covering-glass. The triangular grains of pollen will be seen sending out from one angle a tube into the stigmatic tissue, which is easily seen from its slight difference in colour. The entrance of the pollen-tube into the micropyle can be readily made out in some species of Veronica. The common V. Serpyllifolia—often to be found in shady places on lawns—is well adapted for the pur- pose. A flower should be taken from which the corolla has just dropped. Dissect out the minute ovary and using the dissecting microscope open with a needle one of its two cells in a drop of water; remove the mass of ovules and gently tease them apart. Then put on a covering-glass and examine with a low power till an ovule is found which shews the entry of the pollen-tube. The addition of dilute glycerine will make the ovule more transparent so that after some time the embryo-sac can be seen and the progress of the pollen-tube into the ovule followed. The young fruit of Campanula (especially the com- mon Canterbury Bells of gardens, Campanula Medium) is convenient for examining the embryo-sac. It is only necessary to cut thin transverse sections of the fruit and examine in water. Some of the ovules cut through will allow the embryo-sac to be seen, and in fortunate sections the embryo-vesicle and the end of the pollen-tube in contact with the embryo-sac. IX. THE BELL-ANIMALCULE (Vorticella). THE great majority of those animal organisms which are more complex than Amba, begin their existence as simple nucleated cells, having a general similarity to Ameba; and the single nucleated cell which constitutes the whole animal in its primitive condition divides and subdivides until an aggregation of similar cells is formed. And it is by the. differentiation and metamorphosis of these primitively similar histological elements that the organs and tissues of the body are built up. But in one group, the Jnfusoria, the protoplasmic mass which constitutes the germ does not undergo this process of preliminary subdivision, but such structure as the adult animal possesses is the result of the direct metamorphosis of parts of its protoplasmic substance. Hence, morphologically, the bodies of these animals are the equivalents of a single cell; while, physiologically, they may attain a considerable amount of complexity. The Infusoria abound in fresh and salt waters, and make their appearance in infusions of many animal and vegetable substances, their germs either being contained in the sub- stances infused, or being wafted through the air. Their diffusion is greatly facilitated by the property which many of them possess of being dried, and thus reduced to the condition of an excessively light dust, without the destruction x. THE BELL-ANIMALCULE. 87 f their vitality; while their rapid propagation is, in the nain, due to their power of multiplying by division, with ex- vaordinary rapidity, when duly supplied with nourishment. Che majority are free and provided with numerous cilia by vhich they are incessantly and actively propelled through ‘he medium in which they live; but some attach themselves 0 stones, plants, or even the bodies of other animals, A ew are parasitic, and the bladder and intestines of the Frog re usually inhabited by several species of large size. The Bell-animalcules are Infusoria which are fixed, isually by long stalks, to water-plants, or, not unfrequently, o the limbs of aquatic Crustacea. The body has the shape f a wine-glass with a very long and slender stem, provided rith a flattened disc-like cover. What answers to the rim f the wine-glass is thickened, somewhat everted, and richly iliated, and the edges of the disc are similarly thickened nd ciliated. Between the thickened edge of the cover, or eristome, and the edge of the disc, is a groove, which, at one oint, deepens and passes into a wide depression, the vesti- ulum. From this a narrow tube, the esophagus, leads into ae central substance of the body, and terminates abruptly aerein; and when fecal matters are discharged, they make aeir way out by an aperture which is temporarily formed in ae floor of this vestibule. The outermost layer of the sub- vance of the body is denser and more transparent than the ast, forming a cuticula. Immediately beneath the cuticle it : tolerably firm and slightly granular, and this part is dis- nguished as the cortical layer; it passes into the central ibstance, which is still softer and more fluid. In the undisturbed condition of the Bell-animalcule, the em is completely straightened out; the peristome is everted, id the edges of the disc separated from the peristome; the astibule gaping widely and the cilia working vigorously. ut the least shock causes the disc to be retracted, and the 88 ELEMENTARY BIOLOGY. [ix edge of the peristome to be curved in and shut against it, so as to give the body a more globular form. At the same time, the stem is thrown into a spiral, and the body is thus drawn back towards the point of attachment. If the dis- turbing influence be continued, this state of retraction per- sists; but if it be withdrawn, the spirally coiled stem slowly straightens, the peristome expands, and the cilia resume their activity. In the interior of the body, immediately below the disc, a space, occupied by a clear watery fluid, is seen to make its appearance at regular intervals—slowly enlarging until it attains its full size and then suddenly and rapidly dis- appearing by the approximation of its walls. This is the contractile vesicle. Whether it has any communication with the exterior or not and what is its function, are still open questions. If the Bell-animalcule is well fed, one or more _ watery vesicles of a spheroidal form, each containing a certain portion of the ingested food, will be seen in the soft central mass of the body. And by mixing a small quantity of finely divided carmine or indigo with the water in which the Vorticelle live, the manner in which these food-vesicles are formed may be observed. The coloured particles are driven into the vestibule by the action of the cilia of the peristome and the adjacent parts and gradually accumulate at the inner end of the gullet. After a time the mass here heaped together projects into the central substance of the body, surrounded by an envelope of the accompanying water; and then suddenly breaks off, as a spheroidal drop, hence- forward free in. the soft central substance. In some Bell- animalcules, the food-vesicles thus formed undergo a move- ment of circulation, passing up one side of the body, then crossing over below the disc and descending on the other side. Sooner or later the contents of these vesicles are digested, and the refuse is thrown into the vestibule by an Ix.] THE BELL-ANIMALCULE. 89 aperture which exists only at the moment of extrusion of the feeces, and is indistinguishable at any other time. A portion of the substance of the body, which is slightly different in transparency and in its reactions to colouring substances from the rest, is called the nucleus or. endoplast. It is elongated and bent upon itself into a crescentic or horse- shoe shape. The Bell-animalcules multiply in two ways; partly by longitudinal fission, when a bell becomes cloven down the middle, each half acquiring the structure previously possessed by the whole; and partly by gemmation from the endoplast, in which latter case the endoplast divides and one or more of the rounded masses thus separated are set free as loco- motive germs. Sometimes a rounded body, encircled by a ring of cilia but having otherwise the characters of a Vorticella bell, is seen to be attached to the base of the bell of an ordinary Vorticella. It was formerly supposed that these were buds but it appears that they are independent individuals, which have attached themselves to that to which they adhere and are gradually becoming fused with it, so that the two will form one indistinguishable whole. It is probable that this “con- jugation” has relation to a sexual process. Under certain circumstances a Vorticella may become encysted. The peristome closes and the bell becomes con- verted into a spheroidal body, in which only the nucleus and the contractile vesicle remain distinguishable. This sur- rounds itself with a structureless envelope or cyst, from which, after remaining at rest for a longer or shorter time, the Bell-animalcule may emerge and resume its former state of existence. In thus passing into a temporary condition of rest many of the other Infusoria resemble Vorticella. The two genera of Infusoria which most commonly occur in the Frog are Nyctotherus and Balantidium. Both are free 90 ELEMENTARY BIOLOGY. [Ix. and actively locomotive, and the former is particularly re- markable for its relatively large size and semilunar contour, and for the length and distinctness of its curved cesophagus. Balantidiwm is pyriform, and has a very short cesophageal depression. LABORATORY WORK. A. Examine duckweed roots, conferve, &c, with 1 inch objective avoiding pressure; having found a group of Vorticelle note the following points with a higher power. 1. In the extended state of the animal. a, The body. a. Its size (measure). b. Form; broadly speaking, that of an inverted bell: note— a, The prominent everted rim (peristome). 8. The flattened central disc projecting above the peristome. y. The cilia fringing the disc. 6. The depression between the peristome and disc. e. The mouth of the chamber (vestibulwm) into which the cesophagus and anus open, in the hollow between the peristome and dise. c. Structure :-— a. The thin, transparent, homogeneous external layer (cutzcle). Ix. ] THE BELL-ANIMALCULE, 91 The granular layer (cortical layer) inside the cuticle. [Its fine transverse striation. ] - The central more fluid part, not sharply marked off from £. The various clear spaces (alimentary vacuoles) in it, containing foreign (swallowed) bodies (Diatoms, Protococcus, &c.). The contractile vesicle; its position, in the cortical layer just beneath the disc; its systole and diastole. The nucleus; an elongated curved body in the cortical layer; sometimes nearly homogeneous, sometimes more distinctly granular. The nu- cleus is usually indistinguishable until after treatment with iodine (4). The gullet; sometimes seen in optical trans- verse section as a clear round space; some- times seen sidewise as a canal opening above on the disc, and ending abruptly below in the body-substance.' b. The stalk. Its length and diameter (measure). Its structure; the external homogeneous layer (sheath) continuous with the cuticle ; the highly refractive centre (avis) generally surrounded with granules, and continuous with the cortical layer of the bell. 2. In the retracted state. The body. Its form; pear-shaped; rounded off above; no disc or peristome visible. 92 ¥- ELEMENTARY BIOLOGY. [Ix. The clear transverse space near the top, indica- ting the interval between the retracted disc and the rolled-in peristome. In this space the cilia can frequently be seen moving. Structure; as in 1. ac. b. The stalk ; thrown into corkscrew-like folds. The movements of Vorticella. Compare especially the regularity, definiteness and rapidity of some of them with the slow and irregular movements of Amoeba. (IIL) a. [B. The ciliary movement. Examine the cilia carefully; delicate homoge- neous processes; their length, diameter and form ; their position. The continuity of the cilia with the cortical layer.] The function of the cilia; their rapid move- ments, alternately bending and straightening: the co-ordination of these movements; they work in a definite order; note the currents produced in the neighbouring water (if ne- cessary introduce a few particles of carmine under the coverslip); the sweeping of small bodies down the gullet. The movements of the contractile vesicle (see III. A. 3.¢). Tolerably regular rhythmic distension and collapse (diastole and systole). The currents in the central parts of the body carry- ing round the swallowed bodies. (Compare VI. C.) Lhe movements of the animal as a whole. (4 inch or $ inch obj.) 1x.] THE BELL-ANIMALCULE. 93 ‘Its extreme irritability; it contracts on the slightest stimulation: often without any ap- parent cause. The movements which occur in contraction ; the coiling up of the stalk ; the rolling in of the disc. The rapidity of these movements. The mode of re-expansion ; the stalk straightens first; then the peristome is everted; finally the disc and its cilia are protruded. 4. Stain with iodine or magenta; the cuticle uncoloured —the rest stained; the nucleus especially becomes deeply coloured. 5. Treat with acetic acid; the contents soon disappear (except perhaps some swallowed bodies)—the cuticle later or not at all. 6. Note the following points in various specimens— a. [y. (3. Multiplication by fission ; a bell partially divided into two by a vertical fissure starting from the disc. Two complete bells on one stalk; the result of completion of the fission. The development of a basal circlet of cilia by one or both of these bells. Free swimming unstalked bells (detached bells from B)- Conjugation ; the attachment of a small free swim- ming bell to the side of a stalked one. ] Encystation ; the body contracted into a ball and surrounded by a thickened structureless layer, the contractile vesicle being persistently dilated. ] 94 ELEMENTARY BIOLOGY. [rx B. Other forms closely allied to Vorticella which may be met with, and which will do nearly as well for exami- nation, are ;— a. Hpistylis, Bell-shaped animals growing on a branched non-contractile stalk. b. Carchesium.