peor P oats New York State College of Agriculture At Cornell University Sthaca, N.Y. Library I.P. Roberts Collection Gift of Roger M. Roberts. Cornell University Libra Elementary botany. (:a2a2¢s27"047) ‘(biz aBed 9as) VLATOARY SVDAD ELEMENTARY BOTANY BY GEORGE FRANCIS ATKINSON, Pu.B. Professor of Botany in Cornell University SECOND EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1899 ec Ke? A 8 8949 £7) 7¢ Copyright, 1898, BY HENRY HOLT & CO. ROBERT DRUMMOND, PRINTER, NEW YORK. PREPS, UNTIL recent years the prevalent method of teaching botany in the secondary schools, and in the first courses in many col- leges, has been based on the ‘‘analysis’’ of flowers. The method had its impetus in the study of systematic botany pur- sued with such vigor by the pioneers of the science in America. The great progress in our knowledge of the morphology and physiology of plants during the last quarter of this century has changed the whole problem of elementary instruction in botany, and led to almost universal dissatisfaction with the old method of secondary instruction in this subject. It is now generally recognized that a study of the lower plants, like the alge, fungi, liverworts, mosses, and ferns should form a part of a course of secondary education in botany. To meet this end a number of books have sprung into exist- ence during the past few years. If the need for some guid- ance in the selection of topics, and an outline of the character of the study, could be met by zwmber alone of books, this want would be fully met in the new treatises recently published, and there would be no place for the present book. But a judicious selection of a few forms to illustrate function, process, and relationship throughout the wide range of plant life, and the training in logical methods of induction, and accuracy of draw- ing conclusions, is vastly more important in its influence on the character of the pupil, even though he forget all about the plants studied, than the handling of a great variety of objects, and the drawing of haphazard conclusions, which are left to the pupil in a large number of cases by the methods pursued in many of the recent elementary works. iii lv PREFACE. For several years the author has been deeply interested in the teaching of elementary botany, and has had an opportunity to study methods in a practical way, in having charge of the in- struction of a large class of beginners, the majority of whom had never studied the subject before. One of the great diffi- culties encountered in attempting to introduce the study of the lower plants is the fact that these plants are in most cases en- tirely unknown to the pupil. The difficulty does not lie in the attempt to introduce the study of unknown objects. But it lies rather in the attempt to study the lower plants, at the outset, in a more or less thorough manner, to learn their characters, rela- tionships, etc., in order to group them into their natural orders. This is attempting too much for the young beginner, to whom these plants are totally unfamiliar objects. The method followed in this book has been thoroughly tested in practical work. It is to first study some of the life processes of plants, especially those which illustrate the fundamental prin- ciples of nutrition, assimilation, growth, and irritability. In studying each one of these topics, plants are chosen, so far as possible, from several of the great groups. Members of the lower plants as well as of the higher plants are employed, in order to show that the process is fundamentally the same in all plants. Then another process is studied in a similar way, using so far as possible, especially where the lower plants are concerned, the same plant. In this way the mind is centered on this process, and the discovery to the pupil that it is fundamentally the same in such widely different plants arouses a keen interest not only in the plants themselves, but in the method which attends the discovery of this general principle. In the study of the life processes, the topics can be arranged so that they show progres- sion of function. At the same time it is well for the teacher to select for this study of the life processes those plants which represent well the great groups, and show gradual progression of form and struc- ture, and also those which are easily obtained. A second period of the session can then be devoted to study- PREFACE, Vv ing a few representatives of the different groups of the alge, fungi, liverworts, mosses, ferns, and the higher plants. This should be done with special reference to form, reproduction, general classification, progression, and retrogression of parts or organs, in passing from the lower to the higher plants. In taking up this study of representative forms now, if a wise selec- tion has been made in dealing with the life processes, the same plant can be used here in most cases. These plants now are faniuliar to the pupil, and the mind can be centered on form, organs, reproduction, relationship, etc. In this study of gen- eral morphology it is very important that a careful study be made of some of the lower plants, and of the ferns. Here the sexual organs are well formed, and the processes of reproduc- tion can be more easily observed. In the higher plants the sexual organs are very much reduced, and the processes more difficult to observe. It is only through a study of the lower plants that we are able to properly interpret the floral structures, and the sexual organs of the spermatophytes, and to rid our- selves of the erroneous conceptions which the prevalent method of elementary instruction has fixed so firmly on the lay mind. A third period of the elementary course may be employed in studying special morphology of the higher plants. Even here it seems to the author wise that the ‘‘analysis’’ of plants should be deferred until after a general notion of the characters and habit of several of the important families has been obtained. The pupil may be told the names of the several plants used as examples, and emphasis can be laid on ordinal and generic characters, which can then be recognized in many plants with- out resort to a key. The matter of determining the names of plants by the old method can, if desired, be pursued to greater advantage after this critical study of relationships has been made, even though the pupil may pursue it independently at a later time. In the study of plants one should not lose sight of the value of observing plants in their natural surroundings. If judiciously pursued it forms at once a means of healthful recreation, of com- munion with the very soul of nature, and of becoming ac- vi PREFACE. quainted with the haunts, the lives, the successes and failures of plants; the influences of soil, moisture, and other environ- mental conditions upon plants, and, what is also important, the influence which plants exert upon their environment. Classes may be taken into the field, at different seasons of the year, to observe flower and bud formation, pollenation, seed production, seed distribution, germination of seeds and nutrition of the embryo, protection of plants against foes and extremes of weather; the relationships of plants in colonies, and their dis- tribution in plant formations, etc. In all this study a knowl- edge of some of the lower plants is important. It is not intended that the matter in the book should be mem- orized for the purpose of recitations. It should be used as a guide to the practical work, and asareference book. The para- graphs arranged in coarse print are intended in general to indi- cate the studies which will serve as the basis for the practical work by the student. In most cases the material for these studies can be quite easily obtained and the laboratory work is not difficult. The paragraphs in fine print are intended to fur- ther illustrate the subject by discussion and illustration of the more difficult phases of each topic. Some of these can be made the basis for demonstrations by the teacher before the class, and all will serve as a convenient means of getting at the important reference matter by the student in a single book. Suggestions on the study and the taking of notes, etc., by the student are given in the appendix. Acknowledgments.—The author desires here to express his gratefulness to his associates in the botanical department of Cor- nell University who have read the manuscript and have made useful suggestions (Messrs. E. J. Durand, B. M. Duggar, Kk. M. Wiegand, and Professor W. W. Rowlee). Valuable suggestions were also given by Dr. J. C. Arthur, of Purdue University, who kindly read the chapters on physiology, and by Professor W. F. Ganong, of Smith College, who read some of the chapters on ecology and the tables on the homologies of the gymnosperms and angiosperms. PREFACE. vii Ilustrations.—The large majority of the illustrations are new, and were made with especial reference to the method of treatment followed in the text. Most of the photographs were made by the author. Others were contributed by Professor P. H. Mell, of the Alabama Polytechnic Institute, Auburn, Ala.; Professor Rowlee, Cornell University ; Mr. H. J. Webber, Washington, D.C.; by the New Jersey Geological Survey through the courtesy of Mr. Gifford Pinchot, of New York; by Mr. B. M. Duggar, Cornell University, and Mr. Herman von Schrenk, of the Mis- sourl Botanical Garden. Many of the drawings, especially those of microscopic objects, were made by the author; others by Mr. H. Hasselbring, Cor- nell University, and Dr. Bertha Stoneman, now professor of botany in the Huguenot College, Wellington, Cape Colony, South Africa. The drawings to illustrate the gross characters of plants were made by Mr. W. G. Holdsworth, Michigan Agri- cultural College; Mr. Joseph Bridgham, Providence, R. L.; Messrs. W. C. Furlong and W. C. Baker, Cornell University ; and a few by Miss Edna Porter, Buffalo, N. Y., and by Mrs. E. L. Nichols and Mrs. J. G. Needham, Cornell University. Pro- fessor Chas. A. Davis kindly furnished the sketches from which the drawings of the transformed trillium flower were made. Other illustrations have been obtained from the following sources: from the author’s Study of the Biology of Ferns, through the courtesy of the Macmillan Co.; and from the Annals of Botany, Jahrbiicher fiir wissenschaftliche Botanik, Flora, Botanical Gazette, Vines’ Student’s Text Book of Botany, and Warming’s Botany. Above all the author is under great obligations to Professors Ikeno and Hirase, of the Imperial University of Japan, Tokio, for their unparalleled courtesy in sending drawings of the sperma- tozoids, and of fertilization, in cycas and gingko, in advance of their publication. CorNELL UNIVERSITY, June, 1898. CONTENTS. (References are to paragraphs.) PART I.—PHYSIOLOGY. CHAPTER I. PROTOPLASM. The plant spirogyra, 4. Chlorophyll bands in spirogyra, 5. The spirogyra thread consists of cylindrical threads end to end, 6. Protoplasm, 7. Cell-sap in spirogyra, 8. Reaction of protoplasm to certain reagents, 9. Earlier use of the term protoplasm, 11. Proftoplasm in mucor, 12. Mycelium of mucor, 13. Appearance of the protoplasm, 14. Move- ment of the protoplasm in mucor, 15. Test for protoplasm, 16. Protoplasm in nitella, 17. Form of nitella, 18. Inter- node of nitella, 19. Cyclosis in nitella, 20. Test for proto- plasm, 21. Proteplusm in one of the higher plants, 22. Movement of protoplasm in the higher plants, 23. Move- ment of protoplasm in cells of staminal hair of spiderwort, 24. Cold retards the movement, 25. Protoplasm occurs in the living parts of all plants, 26.......-.-....6.. 00.24, page CHAPTER II. ABSORPTION, DIFFUSION, OSMOSE, Osmose in spirogyra, 30. Turgescence, 31. Experiment with beet in salt and sugar solutions, 32. Osmose in the cells of the beet, 34. The coloring matter in the cell-sap does not readily escape from the living protoplasm of the beet, 35. The coloring matter escapes from dead protoplasm, 36. Osmose experiments with leaves, 37. Absorption by root- hairs, 39. Cell-sap a solution of certain substances, 4o. Diffusion through an animal membrane, 41. Importance of these physical processes in plants, 44..--...-...-....-- page x CONTENTS. CHAPTER III. ABSORPTION OF LIQUID NUTRIMENT. Formula for solution of nutrient materials, 46. Plants take liquid food from the soil, 50. How food solutions are car- ried into the plant, 51. How the root-hairs get the watery solutions from the soil, 52. Plants cannot remove all the moisture from the soil, 53. Acidity of root-hairs, 56...page CHAPTER IV. TURGESCENCE. Turgidity of plant parts, 58. Restoration of turgidity in shoots, 59. Tissue tensions, 61. Longitudinal tissue tension, 62. TATSVETSS UIS6UE LENEICN, 06 c00505 ¢c005e axcaee awwnss pa CHAPTER V. ROOT PRESSURE. Root pressure may be measured, 67. Experiment to demon- Strate root pressure, 68... 260 bees meee Gee eee page CHAPTER VI. TRANSPIRATION. Loss of water from excised leaves, 71. Loss of water from growing plants, 72. Water escapes trom the surfaces of living leaves in the form of water vapor, 73. Experiment to compare loss of water in a dry and a humid atmosphere, 74. The loss of water is greater ina dry than in a humid atmosphere, 75. How transpiration takes place, 76. Struc- ture of a leaf, 79. Epidermis of the leaf, 80. Soft tissue of the leaf, 81. Stomata, 82. The living protoplasm re- tards the evaporation of water from the leaf, 83. Action of the stomata, 84. Transpiration may be in excess of root pressure, 85. Negative pressure, 86. Lifting power of transpiration, 87. Root pressure may exceed transpiration, 88. Injuries caused by excessive root pressure, 89. Dem- onstration of stomates and intercellular spaces, 92..... page CONTENTS. CHAPTER VII. PATH OF MOVEMENT OF LIQUIDS IN PLANTS. Place the cut ends of leafy shoots in u solution of some red dye, 94. These solutions color the tracts in the stem and leaves through which they flow, 95. Structure of the fibro-vascu- lar bundles, 98. Woody portion of the bundle, 99. Bast portion of the bundle, 100. Cambium region of the bundle, tor. Longitudinal section of “the bundle, 102. Vessels or ducts, 103. Sieve tubes, 105. Fibro-vascular bundle in In- dian corn, 107. Rise of water in the vessels, 108. Synopsis Of TISSUES; TIO: cscs wusananaeenas aaasies GRRE Aa use Sen page CHAPTER VIII. DIFFUSION OF GASES. Gas given off by green plants in the sunlight, 111. What this gas is, 117. Oxygen given off by green land plants also, 118. Absorption of carbon dioxide, 119. The gases are exchanged in the plants, 122. A chemical change of the gas takes place within the plant cell, 123. Gases as well as water can diffuse through the protoplasmic membrane, I24 page CHAPTER IX. RESPIRATION. Oxygen from the air consumed during germination of seed, 127. Carbon dioxide given off during germination, 128. Respi- ration is necessary for growth,130. Energy set free during respiration, 132. Respiration in a leafy plant, 133. Respi- ration in fungi, 134. Respiration in plants in general, 135. Respiration a breaking-down process, 136. Detailed result of the above experiment, 137. Another way of performing the experiment, 138. Intramolecular respiration, 139..page CHAPTER X. THE CARBON FOOD OF PLANTS. Starch formed as a result of carbon conversion, 141. Iodine used as atest for starch, 142. Schimper’s method of testing xii CONTENTS. for the presence of starch, 143. Green parts of plants form starch when exposed to the light, 147. Starch is formed only in the green parts of plants, 148. Translocation of starch, 149. Starch in other parts of plants than the leaves, 1st, Form of starch grains, 153... 56.062 :ssseseaseees page CHAPTER XI. CHLOROPHYLL AND FORMATION OF STARCH. @ Fungi cannot form starch, 155. Etiolated plants cannot convert carbon, 156. Chlorophyll and chloroplasts, 157. Form of the chlorophyll bodies, 158. Chlorophyll is a pigment which resides in the chloroplast, 159. Chlorophyll absorbs energy from sunlight for carbon conversion, 160. Rays of light concerned in carbon conversion, 161. Starch grains formed in the chloroplasts, 162. Carbon conversion in other than green plants, 164. Influence of light on the movement of chlorophyll bodies; 165.2% casa cards kacueaeal ooo sequences page CHAPTER XII. NUTRITION; MEMBERS OF THE PLANT BODY. Nutrition of liverworts, 167. Riccia, 167. Marchantia, 168. Frullania, 169. Nutrition in the mosses, 170. The plant body, 171. Members of the plant body, 172. Stem series, 173. Leaf-series, 174: The root, 175s s cass Feuceode Sos eae eH SERA Sp Ohta eo page 322 CHAPTER XLVIII. DIMORPHISM OF FERNS. Dimorphism in the leaves of ferns, 624. The sensitive fern, 625. Transformation of the fertile leaves of onoclea to sterile ones,626. The sporangia decrease as the fertile leaf expands, 628. The ostrich fern, 629. Dimorphism in tropi- Cal ‘ferns, '630cc0 _— SAX cover glass SvEE a tuft of the branches ee ; near the growing end. Examined with — the microscope the green chlorophyll bodies, which form oval or oblong discs, are seen to be very numer- ous. They lie quite closely side by side and form in perfect rows along the inner surface of the wall. One peculiar feature of the arrangement of the chlorophyll bodies is that there are two lines, extending from one end of the internode to the other on opposite sides, where the chlorophyll bodies are wanting. ‘These are known as neutral lines. They run parallel with the axis of the internode, or in a more or less spiral manner as shown in fig. 9. 20. Cyclosis in nitella.—The chlorophyll bodies are stationary on the inner surface of the wall, but if the microscope be properly focussed just beneath this layer we notice a rotary motion of particles in the protoplasm. There are small granules and quite large masses of granular matter which glide slowly along in one direction on a given side of the neutral line. If now we examine the protoplasm on the other side of the neutral line, we see that the movement is in the opposite direction. If we examine this move- ment at the end of an internode the particles are seen to glide around the end from one side of the neutral line to the other. So that when conditions are favorable, such as temperature, healthy state of the plant, etc., this gliding of the particles or apparent streaming of the proto- plasm down one side of the “* cell,’? and back upon the other, continues in Fig. 8. Portion of plant nitella. an uninterrupted rotation, or cyc/os’s. There are many nuclei in an internode of nitella, and they move also. 21. Test for protoplasm.—If we treat the plant with a solution of iodine we get the same reaction as in the case of spirogyra and mucor. The proto- we becomes yellowish brown. 22. Protoplasm in one of the higher plants.—We now wish to examine, and test for, protoplasm in one of the higher plants. 10 PHYSIOLOGY. Young or growing parts of any one of various plants—the petioles of young leaves, or young stems of growing plants—are suitable for study. Tissue from the pith of corn (Zea mays) in young shoots just back of the growing point or quite near the joints of older but growing corn stalks fur- BBG: nishes excellent material. Cyclosis in nitella. If we should place part of the stem of this plant under the microscope we should find it too opaque for observation of the interior of the cells. This is one striking difference which we note as we pass from the low and simple plants to the higher and more complex ones ; not only in general is there an increase of size, but also in general an increase in thickness of the parts. The cells, instead of lying end to end or side by side, are massed together so that the parts are quite opaque. In order to study the interior of the plant we have selected it must be cut into such thin layers that the light will pass readily through them. For this purpose we section the tissue selected by making with a razor,.or other very sharp knife, very thin slices of it. These are mounted in water in the usual way for microscopic study. In his_section_we i e polygonal in form, This is brought about by mutual pressure of all the cells. The granular protoplasm is seen to form a layer just inside the wall, which is connected with the nuclear layer by radiating strands of the same substance. The nucleus does not alw, e at middle of the cell, but often is near one ee ve aes, Bt with alcohol and treat with iodine the characteristic yellowish- brown color appears. So we conclude here also that this sub- stance is identical with the living matter in the other very differ- ent plants which we have studied. 23. Movement of protoplasm in the higher plants.—Cer- tain parts of the higher plants are suitable objects for the study of the so-called streaming movement of protoplasm, especially the delicate hairs, or thread-like outgrowths, such as the silk of PROTOPLASM. II corn, or the delicate staminal hairs of some plants, like those of the common spiderwort, tradescantia, or of the tradescantias grown for ornament in greenhouses and plant conservatories. Sometimes even in the living cells of the corn plant which we have just studied, slow streaming or gliding movements of the granules are seen along the strands of protoplasm where they radiate from the nucleus. 24. Movement of protoplasm in cells of the staminal hair of “« spiderwort.’’—A cell of one of these hairs from a stamen of a tradescantia grown in glass houses is shown in fig. 10. The Fig. 10. Cell from stamen hair of tradescantia showing movement of the protoplasm, nucleus is quite prominent, and its location in the cell varies con- siderably in different cells and at different times. There is a layer of protoplasm all around the nucleus, and from this the strands of protoplasm extend outward to the wall layer. The large spaces between the strands are, as we have found in other cases, filled with the cell-sap. An entire stamen, or a portion of the stamen, having several hairs attached, should be carefully mounted in water. Care should be taken that the room be not cold, and if the weather is cold the water in which the preparation is mounted should be warm. With these precautions there should be little diffi- culty in observing the streaming movement. The movement is detected by observing the gliding of the granules. These move down one of the strands from the nucleus along the wall layer, and in towards the nucleus in another strand. After a little the direction of the movement in any one portion may be reversed. 25. Cold retards the movement.—While the protoplasm is moving, if we rest the glass slip on a block of ice, the move- ment will become slower, or will cease altogether. Then if we 12 PHYSIOLOGY. warm the slip gently, the movement becomes normal again. We may now apply here the usual tests for protoplasm. The result is the same as in the former cases, 26. Protoplasm occurs in the living parts of all plants.— In these plants representing such widely different groups, we find a substance which is essentially alike in all. Though its arrange- ment in the cell or plant body may differ in the different plants or in different parts of the same plant, its general appearance is the same. ‘Though in the different plants it presents, while alive, varying phenomena, as regards mobility, yet when killed and subjected to well known reagents the reaction is in general identical. Knowing by the experience of various investigators that protoplasm exhibits these reactions under given conditions, we have demonstrated to our satisfaction that we have seen proto- plasm in the simple alga, spirogyra, in the common mould, mucor, in the more complex stonewort, nitella, and in the cells of tissues of the highest plants. 27. By this simple process of induction of these facts concerning this substance in these different plants, we have learned an im- portant method in science study. Though these facts and deduc- tions are well known, the repetition of the methods by which they are obtained on the part of each student helps to form habits of scientific carefulness and patience, and trains the mind to logical processes in the search for knowledge. 28. While we have by no means exhausted the study of protoplasm, we can, from this study, draw certain conclusions as to its occurrence and appearance in plants. Protoplasm is found in the living and growing parts of all plants. It is a semi-fluid, or slimy, granular, substance ; in some plants, or parts of plants, the protoplasm exhibits a streaming or gliding movement of the gran- ules. It is irritable. In the living condition it resists more or less for some time the absorption of certain coloring substances. The water may be with- drawn by glycerine. The protoplasm may be killed by alcohol. When treated with iodine it becomes a yellowish-brown color, CHAPTER Il. ABSORPTION, DIFFUSION, OSMOSE. 29. We may next endeavor to learn how plants absorb water or nutrient substances in solution. There are several very instructive experiments, which can be easily performed, and here again some of the lower plants will be found useful. 30. Osmose in spirogyra.—Let us mount a few threads of this plant in water for microscopic examination, and then draw under the cover glass a five per cent solution of ordinary table salt (NaCl) with the aid of filter paper. We shall soon see that the result is similar to that which was obtained when glycer- ine was used to extract the water from the cell-sap, and to con- tract the protoplasmic membrane from the cell wall. But the process goes on evenly and the plant is not injured. The proto- plasmic layer contracts slowly from the cell wall, and the move- ment of the membrane can be watched by looking through the microscope. ‘The membrane contracts in such a way that all the contents of the cell are finally collected into a rounded or oval mass which occupies the center of the cell. If we now add fresh water and draw off the salt solution, we can see the protoplasmic membrane expand again, or move out in all directions, and occupy its former position against the inner surface of the cell wall. This would indicate that there is some pressure from within while this process of absorption is going on, which causes the membrane to move out against the cell wall. The salt solution draws water from the cell-sap. There is thus a tendency to form a vacuum in the cell, and the pressure on the outside of the protoplasmic membrane causes it 2 13 14. PHYSIOLOGY. to move toward the center of the cell. When the salt solution is removed and the thread of spirogyra is again bathed with water, the movement of the water is award in the cell. ‘This would suggest that there is some substance dissolved in the cell-sap which does not readily filter out through the membrane, but draws on the water outside. It is this which produces the pressure from within and crowds the mem- brane out against the cell wall again. Fig. 13. Spirogyra from salt solution into water. Fig. cx. Spirogyra before placing in salt solu- tion. Spirogyra in 5% salt solution. Fig. 12. 81. Turgescence.—Were it not for the resistance which the cell wall offers to the pressure from within, the delicate proto- ABSORPTION, DIFFUSION, OSMOSE. 15 plasmic membrane would stretch to such an extent that it would be ruptured, and the protoplasm therefore would be killed. If % we examine the cells at the ends of the threads of spirogyra we shall see in most cases that the cell wall at the free end is arched _ outward. This is brought about by the press- Before treatment with salt ~=->—— solution. = es Ga ee ure from within ~* Fig. 15. upon the proto- After treatment with plasmic mem- salt solution. brane which itself presses against ~*& the cell wall, and causes it to Fig. 16. arch outward This is beauti- From salt solution placed in water. Figs. 14-16.—Osmosis in threads of mucor. fully shown in the case of threads which are recently broken. The cell wall is therefore e/astc; it yields to a certain extent to the pressure from within, but a point is soon reached beyond which it will not stretch, and an equilibrium then exists between the pressure from within on the protoplasmic membrane, and the pressure from without by the elastic cell wall. This state of equilibrium in a cell is /urges- cence, or such a cell is said to be /urgescent, or turgid. 32. Experiment with beet in salt and sugar solutions.— We may now test the effect of a five per cent salt solution on a portion of the tissues of a beet or carrot. Let us cut several slices of equal size and about 5mm in thickness. Immerse a few slices in water, a few in a five per cent salt solution and a few in a strong sugar solution. It should be first noted that all the slices are quite rigid when an attempt is made to bend them between the fingers. In the course of one or two hours or less, 16 PHYSIOLOGY. if we examine the slices we shall find that those in water remain, as at first, quite rigid, while those in the salt and sugar solutions are more or less flaccid or limp, and readily bend by pres- Fig. 17. Fig. 18. Fig. 19. Before treatment with salt After treatment with salt From saltsolution into water solution. solution. again. Figs. 17-19.—Osmosis in cells of Indian corn. sure between the fingers, the specimens in the salt solution, perhaps, being more flaccid than those in the sugar solution. The salt solution, we judge after our experiment with spirogyra, Fig. 20. Fig, 21. Fig. 22. Rigid condition of fresh beet Limp condition after lying i igi i ‘ : section. fi salt solution. ving in Rigid again after lying again in water, Figs. 20-22.—Turgor and osmosis in slices of beet. withdraws some of the water from the cell-sap, the cells thus losing their turgidity and the tissues becoming limp or flaccid from the loss of water. ABSORPTION, DIFFUSION, OSMOSE. 17 33. Let us now remove some of the slices of the beet from the sugar and salt solutions, wash them with water and then immerse them in fresh water. In the course of thirty minutes to one hour, if we examine them again, we find that they have regained, partly or completely, their rigidity. Here again we infer from the former experiment with spirogyra that the sub- stances in the cell-sap now draw water inward; that is, the diffusion current is inward through the cell walls and the proto- plasmic membrane, and the tissue becomes turgid again. 34. Osmose in the cells of the beet.—We should now make a section of the fresh tissue of a red colored beet for examination with the microscope, and treat this section with the salt solution. Here we can see that the effect of the salt solution is to draw water out of the cell, so that the protoplasmic mem- Fig. 23. Fig. 24. Fig. 25. Before treatment with salt After treatment with salt Later stage of the same. solution. solution. Figs. 23-25.—Cells from beet treated with salt solution to show osmosis and movement of the protoplasmic membrane. brane can be seen to move inward from the cell wall just as was observed in the case of spirogyra.* Now treating the section with water and removing the salt solution, the diffusion current is in the opposite direction, that is in- * We should note that the coloring matter of the beet resides in the cell- sap. It is in these colored cells that we can best see the movement take place, since the red color serves to differentiate well the moving mass from the cell wall. The protoplasmic membrane at several points usually clings tena- ciously so that at several places the membrane is arched strongly away from the cell wall as shown in fig. 24. While water is removed from the cell-sap, we note that the coloring matter does not escape through the protoplasmic membrane, 18 PHYSIOLOGY. ward through the protoplasmic membrane, so that the latter is pressed outward until it comes in contact with the cell wall again, which by its elasticity soon resists the pressure and the cells again become turgid. 85. The coloring matter in the cell-sap does not readily escape from the living protoplasm of the beet.—The red coloring matter, as seen in the sec- tion under the microscope, does not escape from the cell-sap through the pro- toplasmic membrane. When the slices are placed in water, the water is not colored thereby. The same is true when the slices are placed in the salt or sugar solutions. Although water is withdrawn from the cell-sap, this coloring substance as ey echt af if it does it escapes slowly ene. after a consider- able time. PEt, 2 pot VBA 36. The wo matter escapes Bea ede porn tp however, we heat the water containing a slice of beet up to a point which is sufficient to kill the protoplasm, the red coloring matter in the cell-sap filters out through the protoplasmic membrane and colors the water. If we heat a preparation made for study under the microscope up to the thermal death point we can see here that the red coloring matter escapes through the membrane into the water outside. This teaches that certain substances cannot readily filter through the living membrane of protoplasm, but that they can filter through when the protoplasm is dead. A very important condition, then, for the suc- cessful operation of some of the physical processes connected with absorption in plants is that the protoplasm should be in a living condition. 37. Osmose experiments with leaves.—We may next take the leaves of certain plants like the geranium, coleus or other plant, and place them in shallow vessels containing water, salt, and sugar solutions respectively. The leaves should be immersed, but the petioles should project out of the water or solutions. Seedlings of corn or beans, especially the latter, may also be placed in these solutions, so that the leafy ends are immersed. After one or two hours an examination shows that the specimens in the water are still turgid. But if we lift a leaf or a bean plant from the salt or sugar solution, we find that it is flaccid and limp. The blade, or lamina, of the leaf droops as if wilted, though it is still wet. The bean seedling also is flaccid, the succulent stem bending nearly double as the lower part of the stem is held upright. This loss of turgidity is brought about by the loss of water from the tissues, and judging from the experiments on spirogyra and the beet, we con- clude that the loss of turgidity is caused by the withdrawal of some of the water from the cell-sap by the strong salt solution. 38. Now if we wash carefully these leaves and seedlings, which have been in the salt and sugar solutions, with water, and then immerse them in fresh water for a few hours, they will regain their turgidity. Here again we are led to infer that the diffusion current is now inward through the protoplasmic membranes of all the living cells of the leaf, and that the resulting turgidity of the individual cells causes the turgidity of the leaf or stem. ABSORPTION, DIFFUSION, OSMOSE. 19 39. Absorption by root hairs.—If we examine seedlings, which have been grown in a germinator or in the folds of paper or cloths so that the roots will be free from particles of soil, we see near the growing point of the roots that the surface is covered with numerous slender, delicate, thread- like bodies, the root hairs. Let us place a por- tion of a small root containing some of these eo root hairs in water on a glass slip, and prepare it for examination with the microscope. We see that each thread, or root hair, is a continuous tube, or in other words it is a single cell which has become very much elongated. The proto- plasmic membrane lines the wall, and strands of protoplasm extend across at irregular intervals, the interspaces being occupied by the cell-sap. We should now draw under the cover glass some of the five per cent salt solution. The protoplasmic membrane moves away from the cell wall at certain points, showing that plasmolyszs is taking place, that is, the diffusion current is out- ward so that the cell-sap loses some of its water, and the pressure from the outside moves the membrane inward. We should not allow the salt solution to work on the root hairslong. It should be very soon removed by drawing in fresh water before the protoplasmic membrane has been broken at intervals, as is i dh i en on ia ran Fig. 27. Se ee deyetenersne eet apt to be the case by the strong diffusion current and the consequent Root hair of corn strong pressure from ‘ ‘ a 26. : before and alter - Seedling of radish, showing root treatment with 5% without. The membrane hairs. salt solution. # of protoplasm now moves outward as the diffusion current is inward, and soon regains its former position next the inner side of the cell wall. The root hairs then, like other parts of the plant which we have 20 PHYSIOLOGY. investigated, have the power of taking up water under press- ure. 40. Cell-sap a solution of certain substances. —From these experiments we are led to believe that certain substances reside in the cell-sap of plants, which behave very much like the salt solution when separated from water by the protoplasmic membrane. Let us attempt to interpret these phenomena by recourse to diffusion experiments, where an animal membrane separates two liquids of difterent concentration. 41. Diffusion through an animal membrane.—For this experiment we may use a thistle tube, across the larger end of which should be stretched and tied tightly a piece of a bladder membrane, A strong sugar solution (three parts sugar to one part water) is now placed in the tube so that the bulb is filled and the liquid extends part way in the neck of the tube. This is im- mersed in water within a wide-mouth bottle, the neck of the tube being sup- ported in a perforated cork in such a way that the sugar solution in the tube is on a level with the water in the bottle or jar. In a short while the liquid begins to rise in the thistle tube, in the course of several hours having risen several centimeters. The diffusion current is thus stronger through the mem- brane in the direction of the sugar solution, so that this gains more water than it loses. 42. We have here two liquids separated by an animal membrane, water on the one hand which diffuses readily through the membrane, while on the other is a solution of sugar which diffuses through the animal membrane with diff- culty. The water, therefore, not containing any solvent, according to a general law which has been found to obtain in such cases, diffuses more readily through the membrane into the sugar solution, which thus increases in volume, and also becomes more dilute. The bladder membrane is what is sometimes called a diffusion membrane, since the diffusion currents travel through it. 43. In this experiment then the bulk of the sugar solution is increased, and the liquid rises in the tube by this pressure above the level of the water in the jar outside of the thistle tube. The diffusion of liquids through a membrane is osmosis. 44, Importance of these physical processes in plants.—Now if we recur to our experiment with spirogyra we find that exactly the same processes take place. The protoplasmic membrane is the diffusion membrane, through which the diffusion takes place. The salt solution which is first used to bathe the threads of the plant is a stronger solution than that of the cell-sap within the cell. Water therefore is drawn out of the cell-sap, but the substances in solution in the cell-sap do not readily move out. As the bulk of the cell-sap diminishes the pressure from the outside pushes the protoplasmic membrane away from the wall. Now when we remove the salt solution and bathe ABSORPTION, DIFFUSION, OSMOSE. 21 the thread with water again, the cell-sap, being a solution of certain sub- stances, diffuses with more difficulty than the water, and the diffusion current is inward, while the protoplasmic membrane moves out against the cell wall, and turgidity again results. Also in the experiments with salt and sugar solu- tions on the leaves of geranium, on the leaves and stems of the seedlings, on the tissues and cells of the beet and carrot, and on the root hairs of the seed- lings, the same processes take place. These experiments not only teach us that in the protoplasmic membrane, the cell wall, and the cell-sap of plants do we have structures which are capable of performing these physical processes, but they also show that these processes are of the utmost importance to the plant ; not only in giving the plant the power to take up solutions of nutriment from the soil, but they serve also other pur- poses, as we shall see later. CHAPTER III. ABSORPTION OF LIQUID NUTRIMENT. 45. We are now ready tq inquire how plants obtain food from the soil or water. Chemical analysis shows that certain mineral substances are common constituents of plants. By growing plants in different solutions of these various substances it has been possible to determine what ones are necessary constitu- ents of plant food. While the proportion of the mineral ele- ments which enter into the composition of plant food may vary considerably within certain limits, the concentration of the solu- tions should not exceed certain limits. A very useful solution is one recommended by Sachs, and is as follows : 46. Formula for solution of nutrient materials: Water cs tniacsawsaeiagad qayaoamtauiie axel 1000 cc, PoOtassiMMMItale cd. :jue vin ormaamannmernid en 0.5 gr. SOG CHIGHAS a0.4 5:4. se ate ceatm crneubayiondy ee ee 0.5 ‘f Calcinmsulphatécs <2. 04 svixeda tegen ess ae O35 Magiiésium Sulphate s.scs 2.22ce2snecnenes 0.5 ‘ Calciuit PHOSPN ALC. cei jes nee Rcjermcavecitic ayesriuen O.5. ** The calcium phosphate is only partly soluble. The solution which is not in use should be kept in a dark cool place to prevent the growth of minute alge. 47. Several different plants are useful for experiments in water cultures, as peas, corn, beans, buckwheat, etc. The seeds of these plants may be germi- nated, after soaking them for several hours in warm water, by placing them between the folds of wet paper on shallow trays, or in the folds of wet cloth. The seeds should not be kept immersed in water after they have imbibed enough to thoroughly soak and swell them. At the same time that the seeds are placed in damp paper or cloth for germination, one lot of the soaked seeds 22 ABSORPTION NUTRIMENT. 23 should be planted in good soil and kept under the same temperature condi- tions, for control. When ghe plants have germinated one series should be grown in distilled water, which possesses no plant food; another in the nutrient solution, and still another in the nutrient solution to which has been added a few drops of a solution of iron chloride or ferrous sulphate. There would then be four series of cultures which should be carried out with the same kind of seed in each series so that the comparisons can be made on the same species under the different conditions, The series should be numbered and recorded as follows : No. 1, soil. No. 2, distilled water. No. 3, nutrient solution. No, 4, nutrient solution with a few drops of iron solution added. 48. Small jars or wide-mouth bottles, or crockery jars, can be used for the water cultures, and the cultures are set up as follows: A cork which will just fit in the mouth of the bottle, or which can be supported by pins, is perforated so that there is room to insert the seedling, with the root projecting below into the liquid. The seed can be fastened in position by insert- ing a pin through one side, if it is a large one, or in the case of small seeds a cloth of a coarse mesh can be tied over the mouth of the bottle instead of using the cork. After properly set- ting up the experiments the cultures should be arranged in a suitable place, and observed from time to time during several weeks, In order to obtain more satisfactory results several dupli- cate series should be set up to guard against the error which might arise from variation in indi- vidual plants and from accident. Where there are several students in a class, a single series set up by several will act as checks upon one another. If glass jars are used for the liquid Fig. 28. cultures they should be wrapped with black Culture cylinder to show position of ‘ corn seedling (Hansen). paper or cloth to exclude the light from the liquid, otherwise numerous minute algze are apt to grow and interfere with the experiment. Or the jars may be sunk in pots of earth to serve the same purpose. Ifcrockery jars are used they will not need covering. 49. For some time all the plants grow equally well, until the nutriment stored in the seed is exhausted. The numbers I, 3 and 4, in soil and nutri- ent solutions, should outstrip number 2, the plants in the distilled water. No. 4 in the nutrient solution with iron, having a perfect food, compares favor- ably with the plants in the soil. 24 PHYSIOLOGY. 50. Plants take liquid food from the soil.—From these ex- periments then we judge that such plants take up the food they receive from the soil in the form of a liquid, the elements being in solution in water. (See note at close of chapter. ) If we recur now to the experiments which were performed with the salt solution in producing plasmolysis in the cells of spirogyra, in the cells of the beet or corn, and in the root hairs of the corn and bean seedlings, and the way in which these cells become tur- gid again when the salt solution is removed and they are again bathed with water, we shall have an explanation of the way in which plants take up nutrient solutions of food material through their roots. 51. How food solutions are carried into the plant.—We can Fig. 29. Section of corn root, showing rhizords formed from elongated epidermal cells. see how the root hairs are able to take up solutions of plant food, and we must next turn our attention to the way in which these ABSORPTION NUTRIMENT. 25 solutions are carried farther into the plant. We should make a section across the root of a seedling in the region of the root hairs and examine it with the aid of a microscope. We here see that the root hairs are formed by the elongation of certain of the surface cells of the root. These cells elongate perpendicularly to the root, and become 3mm to 6mm long. ‘They are flexuous or irregular in outline and cylindrical, as shown in fig. 29. The end of the hair next the root fits in between the adjacent superfi- cial cells of the root and joins closely to the next deeper layer of cells. In studying the section of the young root we see that the root is made up of cells which lie closely side by side, each with its wall, its protoplasm and cell-sap, the protoplasmic membrane lying on the inside of each cell wall. 52. In the absorption of the watery solutions of plant food by the roct hairs, the cell-sap, being a more concentrated solution, gains some of the former, since the liquid of less concentration flows through the protoplasmic membrane into the more concentrated cell-sap, increasing the bulk of the lat- ter. This makes the root hairs turgid, and at the same time dilutes the cell- sap so that the concentration is not so great. The cells of the root lying in- side and close to the base of the root hairs have a cell-sap which is now more concentrated than the diluted cell-sap of the hairs, and consequently gain some of the food solutions from the latter, which tends to lessen the content of the root hairs and also to increase the concentration of the cell-sap of the same. This makes it possible for the root hairs to draw on the soil for more of the food solutions, and thus, by a variation in the concentration of the sub- stances in solution in the cell-sap of the different cells, the food solutions are carried along until they reach the vascular bundles, through which the solu- tions are carried to distant parts of the plant. Some believe that there is a rhythmic action of the elastic cell walls in these cells between the root hairs and the vascular bundles. This occurs in such a way that, after the cell becomes turgid, it contracts, thus reducing the size of the cell and forcing some of the food solutions into the adjacent cells, when by absorption of more food solu- tions, or water, the cell increases in turgidity again. This rhythmic action of the cells, if it does take place, would act as a pump to force the solutions along, and would form one of the causes of root pressure. 53. How the root hairs get the watery solutions from the soil.—If we examine the root hairs of a number of seedlings which are growing in the soil under normal conditions, we shall see that a large quantity of soil readily clings to the roots. We should note also that unless the soil has been recently watered there is no free water in it ; the soil is only moist, We are curious 26 PHYSIOLOGY. to know how plants can obtain water from soil which is not wet. If we at- tempt to wash off the soil from the roots, being careful not to break away the B oe a” Fig. 30. i Root hairs of corn seedling with soil particles adhering closely. root hairs, we find that small particles cling so tenaciously to + \ the root hairs that they are not removed. Placing a few such root hairs under the microscope it appears as if here and there the root hairs were glued to the minute soil particles. 54, If now we take some of the soil which is only moist, weigh it, and then permit it to become quite dry on exposure to dry air, and weigh again, we find that it loses weight in drying. Moisture has been given oft. This moisture, it has been found, forms an exceedingly thin film on the sur- face of the minute soil particles. Where these soil particles lie closely to- gether, as they usually do when massed together in the pot or elsewhere, this thin film of moisture is continuous from the surface of one particle to that of an- other. Thus the soil particles which are so closely attached to the root hairs connect the surface of the root hairs with this film of moisture. As the cell- sap of the root hairs draws on the moisture film with which they are in con- tact, the tension of this film is sufficient to draw moisture from distant parti- cles. Jn this way the roots are supplied with water in soil which is only moist. 55. Plants cannot remove all the moisture from the soil,—If we now take a potted plant, or a pot containing a number of seedlings, place it in a moder- ately dry room, and do not add water to the soil we find in a few days that the plant is willing. The soil if examined will appear quite dry to the sense of touch. Let us weigh some of this soil, then dry it by artificial ABSORPTION NUTRIMNENT. 27 heat, and weigh again. It has lost in weight. This has been brought about by driving off the moisture which still remained in the soil after the plant began to wilt. This teaches that while plants can obtain water from soil which is only moist or which is even rather dry, they are not able to withdraw all the moisture from the soil. 56. Acidity of root hairs.—If we take a seedling which has been grown in a germinator, or in the folds of cloths or paper, so that the roots are free from the soil, and touch the moist root hairs to blue litmus paper, the paper becomes red in color where the root hairs have come in contact. This is the reaction for the presence of an acid salt, and indicates that the root hairs ex- crete certain acid substances. This acid property of the root hairs serves a very important function in the preparation of certain of the elements of plant food in the soil. Certain of the chemical compounds of potash, phosphoric acid, etc., become deposited on the soil particles, and are not soluble in water. The acid of the root hairs dissolves some of these compounds where the particles of soil are in close contact with them, and the solutions can then be taken up by the roots. 57. This corrosive action of the roots can be shown by the well-known experiment of growing a plant on a marble plate which is covered by soil. After a few weeks, if the soil be washed from the marble where the roots have been in close contact, there will be an outline of this part of the root system. Several different acid substances are excreted from the roots of plants which have been found to redden blue litmus paper by contact. Experiments by Czapek show, however, that the carbonic acid excreted by the roots has the power of directly bringing about these corrosion phenomena, The acid salts are the substances which. are most actively concerned in reddening the blue litmus paper. They do not directly aid in the corrosion phenomena, In the soil, however, where these compounds of potash, phosphoric acid, etc., are which are not soluble in water, the acid salt (primary acid potassium phos- phate) which is most actively concerned in reddening the blue litmus paper may act indirectly on these mineral substances, making them available for plant food. This salt soon unites with certain chlorides in the soil, making among other things small quantities of hydrochloric acid. NoTe.—It should be understood that food substances in solution, during absorption, diffuse through the protoplasmic membrane independently of each ‘other and also independently of the rate of movement of the water from the soil into the root hairs and cells of the root, CHAPTER IV. TURGESCENCE. 58. Turgidity of plant parts.—As we have seen by the experiments on the leaves, turgescence of the cells is one of the conditions which enables the leaves to stand out from the stem, and the lamina of the leaves to remain in an expanded position, so that they are better exposed to the light, and to the currents of air. Were it not for this turgidity the leaves would hang down close against the stem. 59. Restoration of turgidity in shoots.—If we cut off a living stem of geranium, coleus, tomato, or ‘ balsam,’’ and allow the leaves to partly wilt so that the shoot loses its turgidity, it is possible for this shoot to regain turgidity. ‘The end may be freshly cut again, placed ina vessel of water, covered with a bell p jar and kept ina room where the temperature WY is suitable for the growth of the plant. The H,,Ne) from tobacco. All living plants contain a large per cent of water. According to Vines “ripe seeds dried in the air contain 12 to 15 per cent of water, herbaceous plants 60 to $0 per cent, and many water-plants and fungi as much as 95 per cent of their weight.’" When heated to 100° C. the water is driven off. The dry matter remaining is made up partly of organic compounds, examples of which are given above, and inorganic compounds. By burning this dry residue the organic substances are mostiy changed into volatile products, principally carbonic acid, water, and nitrogen. The inorganic substances as a result of combustion remain as a white or gray powder, the ash, The amount of the ash increases with the age of the plant, though the per- centage of ash may vary at different times in the different members of the plant. The following table taken from Vines will give an idea of the amount and composition of the ash in the dry solid of a few plants. CONTENT OF 1000 PARTS OF DRY SOLID MATTER. e| 31 48 | ex | é ¥ 1S Z| Ss | Rs »|2/ai|¢(|e8|6| 32/4") ¢ | 4 3 3 3 ae | @ 5 oe |S 2 || 8 ° a s o aE 3 = s < oy WN Hn a fu Ay n n oO Clover, in blossom. . 68.3 | 21.96] 1.39 | 24.06) 7.44 | 0.72 | 6.74 | 2.06 1.62] 2.66 Wheat, grain........] 19-7 6.14] 0.44 0.66] 2.36 | 0.26 | 9.26 | 0.07 0.42) 0 04 Wheat, straw. G37 7+33| 0.74 3-09} 1 33 | 0.33 | 2.58 | x 32 | 36 25] 0.90 Potato tubers. . 37-7 | 22.76] 0.99 0.97} 1.77 | 0.45 | 6.53 | 2 45 0.80) 1.17 Apples .... .. 14.4 5-14] 3.76 © 59] 1-26 | 0.20 | 1.96 | 0.88 W562) 0 seas Peas (the seed) 27 3 | 11.411 0 26 1.36! 2.17 | 0.16 | 9.95 | 0 95 0.24| 0.42 CHAPTER XI. CHLOROPHYLL AND THE FORMATION OF STARCH. 154. In our experiments thus fur in treating of the absorption of carbon dioxide and the evolution of oxygen, with the accom- panying formation of starch, we have used green plants. 155. Fungi cannot form starch.—If we should extend our experiments to the fungi, which lack the green color so charac- teristic of the majority of plants, we should find that carbon con- version does not take place even though the plants are exposed to direct sunlight. These plants cannot then form starch, but obtain carbohydrates for food from other sources. 156. Etiolated plants cannot convert carbon.—Moreover carbon conversion is usually confined to the green plants, and if by any means one of the ordinary green plants loses its green color carbon conversion cannot take place in that plant, even when brought into the sunlight, until the green color~ has appeared under the influence of light. This may be very easily demonstrated by growing seedlings of the bean, squash, corn, pea, etc. (pine seedlings are green even when grown in the dark), in a dark room, or in a dark receiver of some kind which will shut out the rays of light. The room or receiver must be quite dark. As the seedlings are ‘‘ coming up;’’ and as long as they remain in the dark chamber, they will present some other color than green; usually they are somewhat yellowed. Such plants are said to be e/olafed. If they are brought into the sunlight now for a few hours and then tested for the presence of starch the result will be negative. But if the plant is left in the light, in a few days the leaves begin to take 65 66 PHYSIOLOGY. on a green color, and then we find that carbon conversion begins. 157. Chlorophyll and chloroplasts.—The green substance in plants is then one of the important factors in this complicated process of forming starch. This green substance is ch/orophyll, and it usually occurs in definite bodies, the chlorophyll bodies, or chloroplasts. The material for new growth of plants grown in the dark is derived from the seed. Plants grown in the dark consist largely of water and protoplasm, the walls being very thin. 158. Form of the chlorophyll bodies.—Chlorophyll bodies vary in form in some different plants, especially in some of the lower plants. This we have already seen in the case of spirogyra, where the chlorophyll body is in the form of a very irregular band, which courses around the inner side of the cell wall in a spiral manner. In zygnema, which is related to spirogyra, the chlorophyll bodies are star-shaped. In the desmids the form varies greatly. In cedogonium, another of the thread-like algee, illustrated in fig. 95, the chlorophyll bodies Fig. 55. Section of ivy leaf, Palisade cells above, loose parenchyma, with large intercellular spaces in center. Epidermal cells on either edge, with no chlorophyll bodies. are more or less flattened oval disks. In vaucheria, too, a branched thread-like alga shown in fig. 106, the chlorophyll bodies are oval in outline. These two plants, cedogonium and CHLOROPHYLL; STARCH. 67 vaucheria, should be examined here if possible, in order to be- come familiar with their form, since they will be studied later under morphology (see chapters on cedogonium and vaucheria, for the occurrence and form of these plants). The form of the chlorophyll body found in cedogonium and vaucheria is that which iscommon to many of the green algz, and also occurs in the mosses, liverworts, ferns, and the higher plants. It is a more or less rounded, oval, flattened body. 159. Chlorophyll is a pigment which resides in the chloroplast.—That the chlorophyll is a coloring substance which resides in the chloroplastid, and does not form the body itself, can be demonstrated by dissolving out the chlorophyll when the framework of the chloroplastid is apparent. The green parts of plants which have been placed for some time in alcohol lose their green color. The alcohol at the same time becomes tinged with green. In sectioning such plant tissue we find that the chlorophyll bodies, or chloro- plastids as they are more properly called, are still intact, though the green color is absent. From this we know that chlorophyll is a substance distinct from that of the chloroplastid. 160. Chlorophyll absorbs energy from sunlight for carbon conversion.—It has been found by analysis with the spectroscope that chlorophyll absorbs cer- tain of the rays of the sunlight. The energy which is thus obtained from the-sun, called metic energy, is supposed to act on the molecules of CO, and H,0, separating them into other molecules of C, H, and O, and that after a series of complicated chemical changes starch is formed by the union of mole- cules of carbon, oxygen, and hydrogen, the hydrogen and some of the oxygen at least coming from the water in the cells of the plant. In this process of the reduction of the CO, and the formation of starch there is a surplus of oxygen, which accounts for the giving off of oxygen during the process. 161. Rays of light concerned in carbon conversion.—If a solution of chlorophyll be made, and light be passed through it, and this light be examined with the spectroscope, there appear what are called absorption bands. These are dark bands which lie across certain portions of the spectrum. These bands lie in the red, orange, yellow, green, blue, and violet, but the bands are stronger in the red, which shows that chlorophyll absorbs more of the red rays of light than of the other rays. These are the rays of low refrangibility. The kinetic energy derived by the absorption of these rays of light is transferred into potential energy. That is, the molecule of CO, is broken up, and then by a different combination of certain elements starch is formed.* * In the formation of starch during carbon conversion the separated mole- cules from the carbon dioxide and water unite in such a way that carbon, 68 PHYSIOLOGY. 162. Starch grains formed in the chloroplasts.—During carbon conver- sion the starch formed is deposited generally in small grains within the green chloroplast in the leaf. We can see this easily by examining the leaves of some moss like funaria which has been in the light, or in the chloroplasts of the prothallia of ferns, etc. Starch grains may also be formed in the chloroplasts from starch which was formed in some other part of the plant, but which has passed in solution. Thus the functions of the chloroplast are twofold, that of the conversion of-carbon and the formation of stanch grains. 163. In the translocation of starch when it becomes stored up in various parts of the plant, it passes from the state of solution into starch grains in connection with plastids similar to the chloroplasts, but which are not’ green. The green ones are sometimes called chloroplasts, while the colorless ones are termed devkcaasts, and those possessing “other” colors, as red and yellow, in floral leaves, the root of the carrot, etc., are called chr omoplasts. 164. Carbon conversion in other than green plants.—While carbo- hydrates are usually only formed by green plants, there are some exceptions. Apparent exceptions are found in the blue-green alge, like oscillatoria, nostoc, or inthe brown and red sea weeds like fucus, rhabdonia, etc. These plants, however, possess chlorophyll, but it is disguised by another pigment or color, There are plants, however, which do not have chlorophyll and yet form carbohydrates with evolution of oxygen in the presence of light, as for example a purple bacterium, in which the purple coloring substance absorbs light, though the rays absorbed most energetically are not the red. 165. Influence of light on the movement of chlorophyll bodies. —/x fern prothallia.—lf we place fern prothallia in weak light for a few hours, and then examine them under the microscope, we find that the most of the chloro- phyll bodies in the cells are arranged along the inner surface of the horizontal wall. If now the same prothallia are placed in a brightly lighted place for a short time most of the chlorophyll bodies move so that they are arranged along the surfaces of the perpendicular walls, and instead of having the flattened surfaces exposed to the light as in the former case, the edges of the chlorophyll bodies are now turned toward the light. (See figs. 56, 57-) The same phenomenon has been observed in many plants. Ligit then has an influence on chlorophyll bodies, to some extent determining their position. In weak light they are arranged so that the flattened surfaces are exposed to the incidence of the rays of light, so that the chlorophyll will hydrogen, and oxygen are united into a molecule of starch. This result is usually represented by the following equation: CO, + H,O = CH,O + O,. Then by polymerization 6(CH,O) = C,H,,.0, = grape sugar. Then C,H,,0, — HO = C,H,,0, = starch. It is believed, however, that the process is much more complicated than this, and that several different com- pounds are formed before starch finally appears. CHLOROPHYLL; STARCH. 69 absorb as great an amount as possible of kinetic energy ; but intense light is stronger than necessary, and the chlorophyll bodies move so that their edges are exposed to the incidence of the rays. This movement of the chlorophyll bodies is different from that which takes place in some water plants like Fig. 56. Fig 57. Cell exposed to weak diffused light show- Same cell exposed to strong light, showing ing chlorophyll bodies along the horizontal chlorophyll bodies have moved to perpen- walls. dicular walls. Figs. 56, 57.—Cell of prothallium of fern. elodea. The chlorophyll bodies in elodea are free in the protoplasm. The protoplasm in the cells of elodea streams around the inside of the cell wall much as it does in nitella and the chlorophyll bodies are carried along in the currents, while in nitella they are stationary. CHAPTER XII. NUTRITION AND MEMBERS OF THE PLANT BODY. 166. In connection with the study of the means for obtaining nutriment from the soil or water by the green plants it will be found convenient to observe carefully the various forms of the plant. Without going into detail here the suggestion is made that simple thread forms like spirogyra, cedogo- nium, and vaucheria; expanded masses of cells as are found in the thalluid liverworts, the duckweed, etc., be compared with those liverworts, and with the mosses, where leaf-like expansions of a central axis have been differentiated. We should then note how this differentiation, from the physiological stand- point, has been carried further in the higher land plants. 167. Nutrition of liverworts.—In many of the plants termed liverworts the vegetative part of the plant is a thin, flattened, more or less elongated green body known as a thallus. Riccia.—One of these, belonging to the genus riccia, is shown in fig. 58. Its shape is somewhat like that of a minute ribbon which is forked at intervals ina dichotomous man- ner, the characteristic kind of branching found in these thalloid liverworts. This riccia (known as R. lutescens) occurs on damp soil; long, slender, hair-like % processes grow out from the under surface of the thallus, which resemble root hairs and serve the same purpose in the processes of nutrition. Another species of riccia (R. crystallina) is shown in fig. 171. This plant 3 is quite circular in outline and Fig. 58. occurs on muddy flats. Some Thallus of riccia lutescens. species float on the water. 168. Marchantia.—One of the larger and coarser liverworts is figured at 59. This is a very common liverwort, growing in 20 NUTRITION; MEMBERS PLANT BODY. 71 very damp and muddy places and also along the margins of streams, on the mud or upon the surfaces of rocks which are bathed with the water. This is known as Alarchantia polymorpha. If we examine the under surface of the marchantia we see numerous hair-like processes which attach the plant to the soil. Under the microscope we see that some of these are exactly like the root hairs of the seedlings which we have been studying, and they here serve the same purpose. Since, however, there are no roots on the marchantia plant, these hair-like outgrowths are Fig. 59. Marchantia plant with cupules and gemme ; rhizoids below. usually termed here rizzozds. In marchantia they are of two kinds, one kind the simple ones with smooth walls, and the other kind in which the inner surfaces of the walls are roughened by processes which extend inward in the form of irregular tooth- like points. Besides the hairs on the under side of the thallus we note especially near the growing end that there are two rows of leaf-like scales, those at the end of the thallus curving up over the growing end, thus serving to protect the delicate tissues at the growing point. 72 PHYSIOLOG Y. 169. Frullania.—In fig. 60 is shown another liverwort, anit differs greatly in form from the ones we have just been studying in that there isa well-defined axis with lateral leaf-like outgrowths. Such liverworts are called foliose liverworts. Besides these two quite prominent rows of leaves there is a third row of poorly developed leaves on the under surface. Also from the under surface of the axis we see here and there slender out- =) growths, the rhizoids, through which much Fig. 62 of the liquid Fig. 60. Fig. 61. Under side Portion of plant of Portion of same showing forked nutriment is Frullania, a foliose more highly magni- under -row liverwort. fied, showing over- leaves ana lohes absorbed. lapping leaves. of lateral leaves. 170. Nutrition of the mosses—Among the mosses which are usually common in moist and shaded situations, examples are abundant which are suitable for the study of the organs of absorption. If we take for example a plant of mnium (M. affine) which is illustrated in fig. 64, we note that it consists of a slender axis with thin flat, green, leaf-like expansions. Examin- ing withthe microscope the lower end of the axis, which is attached to the substratum, there are seen numerous brown colored threads more or less branched. (For nutrition of moulds, mushrooms, parasitic fungi, dodder, carnivorous plants, lichens, aquatic plants, etc., see Part III. Ecology.) 171i. The plant body.—In the simpler forms of plant life, as in spirogyra and many of the alge and fungi, the plant body is not differentiated into parts. In many other cases the only differentiation is between the growing part and the fruiting part. In the algee and fungi there is no differentiation into stem and leaf, though there is an approach to it in some of the higher forms. Where this simple plant body is flattened, as in the sea-wrack, or ulva, it is a frond. The Latin word for frond is ¢ad/us, and this name is NUTRITION; MEMBERS PLANT BODY. 73 applied to the plant body of all the lower plants, the alge and fungi. The alge and fungi together are sometimes called the ¢hadlophytes, or thallus plants. The word thallus is also sometimes applied to the flattened body of the liver- worts. In the foliose liverworts and mosses there is an axis with leaf-like expansions. These are believed by some to represent true stems and leaves, by others to represent a flattened thallus in which the margins are deeply and regularly divided, or in which the expansion has only taken place at regular intervals. Fig. 63. Foliose liverwort (bazzania) showing dichotomous branching and overlapping leaves. 172. Members of the plant body.—In the higher plants there is usually great differentiation of the plant body, though in many forms, as in the duck- weeds, it is a frond. While there is great variation in the form and func- tion of the members of the plant body, they are reducible to a few fundamental members. Some reduce these forms to three, the root, stem, and leaf, while others to two, the voot and shoot, which is perhaps the better arrangement. Here the shoot is farther divided into stem and leaf, the leaf being a lateral outgrowth of the stem. The different forms of the members are usually des- ignated by special names, but it is convenient to group them in the single series. Examples are as follows: 173. Stem series. Tubers, underground thickened stems, bearing buds and scale leaves; ex., Trish potato. Root-stocks, underground, usually elongated, bearing scales or bracts, and a leafy shoot; ex., trillium, mandrake, etc. Root-stocks of the ferns bear expanded, green leaves. Runners, slender, trailing, bearing bracts, and leafy stems as branches; ex., strawberry vines. Corms, underground, short, thick, leaf bearing and scale bearing; ex., In- dian turnip. 74 PHVSIOLOGY. Bulbs, usually underground, short, conic, leaf and scale bearing; ex., Female plant (gametophyte) of a moss (mnium), showing rhizoids below, and the tuft of leaves above, which protect the archegonia. lily. Thorns, stout, thick, poorly developed bran- ches with rudiments of leaves (scales); ex., hawthorn. Tendrils, slender reduced stems. Flower axes (see morphology of the angio. sperms). 174. Leaf series.—Besides the foliage leaves, the following are some of their modifications: Flower parts (see morphology of the angio- sperms). Bracts and scales, small, the former usually green (flower bracts), the latter usually: chloro- phylless. Bud scales are sometimes green. Tendrils, modifications of the entire leaf (tendrils of the squash where the branched tendril shows the principal veins of the leaf), modification of the terminal pinnz of the leaf (vetch), etc. Spines (examples are found in the cacti, where the stem is enlarged and green, function- ing as a leaf). Other modifications occur as in the pitcher plant, insectivorous plants, etc. 175. The root shows less modification. Be- sides normal roots, which are fibrous in most small plants and stout in the larger ones, some of the modifications are found in fleshy roots, where nourishment is stored (ex., dahlia, sweet potato, etc.), aerial roots (ex., poison ivy, the twining form), aerial orchids, etc. For modifications of roots due to symbiotic fungi, see chapter on Nutrition in Part III. CHAPTER XIII. GROWTH. 176. By growth is usually meant an increase in the bulk of the plant accompanied generally by an increase in plant sub- stance. Among the lower plants growth is easily studied in some of the fungi. 177. Growth in mucor.—Some of the gonidia (often called spores) may be sown in nutrient gelatine or agar, or even in prune juice. Ifthe culture has been placed in a warm room, in the course of 24 hours, or even less, the preparation will be ready for study. 178. Form of the gonidia.—It will be instructive if we first examine some of the gonidia which have not been sown in the cul- ture medium. We should note their rounded or globose form, as well as their markings if they belong to one of the species with spiny walls. Particularly should we note the size, and if possible measure them with the micrometer, though this would not be absolutely necessary for a comparison, if the comparison can be made immediately. Now examine some of the gonidia which were sown in the nutrient medium. If they have not already germinated we note at once that they are much larger than those which nave not been immersed in a moist medium. 179. The gonidia absorb water and increase in size before germinating.—From our study of the absorption of water or watery solutions of nutriment by living cells, we can easily un- derstand the cause of this enlargement of the gonidium of the mucor when surrounded by the moist nutrient medium. The cell-sap in the spore takes up more water than it loses by diffu- 7 76 PHYSIOLOG ¥. sion, thus drawing water forcibly through the protoplasmic mem- brane. Since it does not filter out readily, the increase in Fig. 65. Spores of mucor, and different stages of germination. quantity of the water in the cell produces a:pressure from within which stretches the membrane, and the elastic cell wall yields. Thus the gonidium becomes larger. 180. How the gonidia germinate.—We should find at this time many of the gonidia extended on one side into a tube-like process the length of which varies according to time and tempera- ture. The short process thus begun continues to elongate. ‘This elongation of the plant is gvozsh, or, more properly speaking, one of the phenomena of growth. 181. The germ tube branches and forms the mycelium.— In the course of a day or so branches from the tube will appear. This branched form of the threads of the fungus is, as we remember, the mycelium. We can still see the point where growth started from the gonidium. Perhaps by this time several tubes have grown froma single one. The threads of the myce- lium near the gonidium, that is, the older portions of them, have increased in diameter as they have elongated, though this increase in diameter is by no means so great as the increase in length. After increasing to a certain extent in diameter, growth in this direction ceases, while apical growth is practically unlimited, being limited only by the supply of nutriment. 182. Growth in length takes place only at the end of the thread.—If there were any branches on the mycelium when the GROWTH. 77 culture was first examined, we can now see that they remain practically the same distance from the gonidium as when they were first formed. That is, the older portions of the mycelium do not elongate. Growth in length of the mycelium is confined to the ends of the threads. 183. Protoplasm increases by assimilation of nutrient substances.—As the plant increases in bulk we note that there is an increase in the protoplasm, for the protoplasm is very easily detected in these cultures of mucor. This increase in the quantity of the protoplasm has come about by the assimilation of the nutrient substance, which the plant has absorbed. The increase in the protoplasm, or the formation of additional plant substance, is another phenomenon of growth quite different from that of elongation, or increase in bulk. 184. Growth of roots.—For the study of the growth of roots we may take any one of many different plants. The seedlings of such plants as peas, beans, corn, squash, pumpkin, etc., serve excellently for this purpose. 185. Roots of the pumpkin.—The seeds, a handful or so, are soaked in water for about 12 hours, and then placed between layers of paper or between the folds of cloth, which must be kept quite moist but not very wet, and should be kept in a warm place. A shallow crockery plate, with the seeds lying on wet filter paper, and covered with additional filter paper, or with a bell jar, an- swers the purpose well. The primary or first root (radicle) of the embryo pushes its way out between the seed coats at the small end. When the seeds are well germinated, select several which have the root 4-5cm long. With a crow-quill pen we may now mark the terminal portion of the root off into very short sections as in fig. 66. The first mark should be not more than 1mm from the tip, and the others not more than 1mm apart. Now place the seedlings down on damp filter paper, and cover with a bell jar so that they will re- main moist, and if the season is cold place them in a warm room. At intervals of 8 or ro hours, if convenient, observe them and note the farther growth of the root. 78 PHYSIOLOGY. 186. The region of elongation.—While the root has elon- gated, the region of elongation 7s no/ at the tip of the root. Ii hes a little distance back from the tip, beginning at about 2mm from the tip and extending over an area represented by from 4-5 of the milli- PACER meter marks. The aoe root shown in fig. 66 Bae, was marked at Io A.M. on July 5. At 6 P.M. of the same day, 8 Fig. 66. Root of germinating pumpkin, showing region of elongation just back of the tip. hours later, growth had taken place as shown in the middle figure. At 9 A.M. on the following day, 15 hours later, the growth is represented in the lower one. Similar experiments upon a number of seedlings gives the same result: the region of elongation in the growth of the root is situated a little distance back from the tip. Farther back very little or no elongation takes place, but growth in diameter continues for some time, as we should discover if we examined the roots of growing pump- kins, or other plants, at different periods. 187. Movement of region of greatest elongation.—In the region of elongation the areas marked off do not all elongate equally at the same time. The middle spaces elongate most rapidly and the spaces marked off by the 6, 7, and 8 mm marks elongate slowly, those farthest from the tip more slowly than the others, since elongation has nearly ceased here. The spaces marked off between the 2-4mm marks also elongate slowly, but soon begin to elongate more rapidly, since that region is becom- ing the region of greatest elongation. Thus the region of greatest elongation moves forward as the root grows, and remains ap- proximately at the same distance behind the tip. 188. Formative region.—If we make a longitudinal section of the tip of a growing root of the pumpkin or other scedling, and examine it with the mi- GROWTH. 79 croscope, we see that there is a great difference in the character of the cells of the tip and those in the region of elongation of the root. First there is in the section a V-shaped cap of loose cells which are constantly being sloughed off. Just back of this tip the cells are quite regularly isodiametric, that is, of equal diameter in all directions. They are also very rich in pro- toplasm, and have thin walls. This is the region of the root where new cells are formed by division. It is the formative region. The cells on the outside of this area are the older, and pass over into the older parts of the root and root cap. If we examine successively the cells back from this formative region we find that they become more and more elongated in the direction of the axis of the root. The elongation of the cells in this older portion of the root explains then why it is that this region of the root elongates more rapidly than the tip. 189. Growth of the stem.—We may use a bean seedling growing in the soil. At the junction of the leaves with the stem there are enlargements. These are the zodes, and the spaces on the stem between successive nodes are the zz/ernodes. Weshould mark off several of these internodes, especially the younger ones, into sections about 5m long. Now observe these at several times for two or three days, or more. The region of elongation is greater than in the case of the roots, and extends back farther from the end of the stem. In some young garden bean plants the region of elongation extended over an area of 4omm in one internode. 190. Force exerted by growth.—One of the marvelous things connected with the growth of plants is the force which is exerted by various members of the plant under certain conditions. Observations on seedlings as they are pushing their way through the soil tothe air often show us that considerable force is required to lift the hard soil and turn it to one side. A very striking illustration may be had in the case of mushrooms which sometimes make their way through the hard and packed soil of walks or roads. That succu- lent and tender plants should be capable of lifting such comparatively heavy weights seems incredible until we have witnessed it. Very striking illustra- tions of the force of roots are seen in the case of trees which grow in rocky situations, where rocks of considerable weight are lifted, or small rifts in large rocks are widened by the lateral pressure exerted by the growth of a root, which entered when it was small and wedged its way in. 191. Zone of maximum growth.—Great variation exists in the rapidity of growth even when not influenced by outside conditions. In our study of the elongation of the root we found that the cells just back of the formative region 80 PHYSIOLOGY. elongated slowly at first. The rapidity of the elongation of these cells in- creases until it reaches the maximum. ‘Then the rapidity of elongation les- sens as the cells come to lie farther from the tip. The period of maximum elongation here is the zone of maximum growth of these cells. 192. Just as the cells exhibit a zone of maximum growth, so the members of the plant exhipit a similar zone of maximum growth, In the case of leaves, when they are young the rapidity of growth is comparatively slow, then it increases, and finally diminishes in rapidity again. So it is with the stem. When the plant is young the growth is not so rapid; as it approaches middle age the rapidity of growth increases; then it declines in rapidity at the close of the season. 193. Energy of growth.—Closely related to the zone of maximum growth is what is termed the energy of growth. This is manifested in the compara- tive size of the members of a given plant. To take the sunflower for example, the lower and first leaves are comparatively small. As the plant grows larger the leaves are larger, and this increase in size of the leaves increases up to a maxi- mum period, when the size decreases until we reach the small leaves at the top ofthe stem. The zone of maximum growth of the leaves corresponds with the maxi- mum size of the leaves on the stem. The rapidity and energy of growth of the stem is also correlated with that of the leaves, and the zone of maximum growth is coincident with that of the leaves. It would be instructive to note it Fig. 67. in the case of other plants Pp Lever auxanometer (Oels) for measuring elongation of and also in the case of the stem during growth. 7 fruits. 194. Nutation.—During the growth of the stem all of the cells of a given section of the stem do not elongate simultaneously. For example the cells at a given moment on the south side are elongating more rapidly than the cells on the other side. This will cause the stem to bend slightly to the north. In a few moments later the cells on the west side are elongating more rapidly, and the stem is turned to the east; and so on, groups of cells in suc- cession around the stem elongate more rapidly than the others. This causes the stem to describe a circle or ellipse about a central point. Since the re- gion of greatest elongation of the cells of the stem is gradually moving toward the apex of the growing stem, this line of clongation of the cells which is GROWTH. 81 traveling around the stem does so ma spiral manner. In the same way, while the end of the stem is moving upward by the elongation of the cells, and at the same time is slowly moved around, the line which the end of the stem describes must be a spiral one. This movement of the stem, which is common to all stems, leaves, and roots, is sation. 195. The importance of nutation to twining stems in their search for a place of support, as well as for the tendrils on leaves or stems, will be seen. In the case of the root it is of the utmost importance, as the root makes its way through the soil, since the particles of soil are more easily thrust aside. The same is also true in the case of many stems before they emerge from the soil, CHAPTER XIV. IRRITABILITY 196. We should now examine the movements of plant parts in response to the influence of certain stimuli. By this time we have probably observed that the direction which the root and stem take upon germination of the seed is not due to the position in which the seed happens to lie. Under normal conditions we have seen that the root grows downward and the stem upward. 197. Influence of the earth on the direction of growth.— When the stem and root have been growing in these directions for a short time let us place the seedling in a horizontal position, so that the end of the root extends over an object of support in such a way that it will be free to go in anydirection. It should be pinned to a cork and placed ina moist chamber. In the course of twelve to twenty-four hours the root which was formerly horizontal has turned the tip downward again. If we should mark off millimeter spaces beginning at the tip of the root, we should find that the motor zone, or region of curvature, lies in the same region as that of the elongation of the root. Knight found that the stimulus which influences the root to turn downward is the force of gravity. The reaction of the root in response to this stimulus is geotropism, a turning influenced by the earth, This term is applied to the growth movements of plants influenced by the earth with regard to direction. While the motor zone lies back of the root tip, the latter receives the stimulus and is the perceptive zone. If the root tip is cut off, the root is no longer geotropic, and will not turn downward when placed in a horizontal position. Growth toward the earth 82 IRRITABILITY. 83 is progeotropism. ‘The lateral growth of secondary roots is da- geotropism. The stem, on the other hand, which was placed in a horizontal position has become again erect. This turning of the stem in Fig. 68. Fig. 69. Germinating pea placed in a hori- In 24 hours gravity has caused the root to zontal position. turn downward. Figs. 68, 69.—Progeotropism of the pea root. the upward direction takes place in the dark as well as in the light, as we can see if we start the experiment at nightfall, or place the plant in the dark. This up- ward growth of the stem is also influ- enced by the earth, and therefore is a case of geotropism. The special desig- nation in the case of upright stems is negative geotropism, or apogeotropism, or the stems are said to be apogeotropic. Fig. 70. Pumpkin seedling showing apogeotropism. Seedling at the left placed hori- zontally, in 24 hours the stem has become erect. If we place a rapidly growing potted plant in a horizontal position by laying the pot on its side, the ends of the shoots will soon turn upward again when placed in a horizontal position. Young bean plants growing in a pot began within two hours to turn the ends of the shoots upward. 84 PHYSIOLOG Y. Horizontal leaves and shoots can be shown to be subject to the same influence, and are therefore dageo/ropic. 198. Influence of light.—Not only is light a very important factor for plants during carbon conversion, it exerts great influ- ence on plant growth and movement. 199. Retarding influence of light on growth.—We have only to return to the experiments performed in growing plants in the dark to see one of the influ- ences which light exerts on plants. The plants grown in the dark were longer and more slender than those grownin the light. Light then has a retarding —_influ- ence on the elong- ation of the stem. 200. Influence Fig. 71. ; \ of light on direc “dark: long, siesder nor green tion of growth.—While we are growing seedlings, the pots or boxes of some of them should be placed so that the plants will Fig. 72. have a one-sided illumination. This can _ Radish seedlings grown in a the light, shorter, stouter, and be done by placing them near an open green in color. Growth re- s ‘4 Z fs * tarded by light. window, in a room with a one-sided illu- mination, or they may be placed in a box closed on all sides but one which is facing the window or light. In 12-24 hours, or even in a much shorter time in some cases, the stems of the seedlings will be directed toward the source of light. This influence exerted by the rays of light is Aeliofropism, a turning influenced by the sun or sunlight. 201. Diaheliotropism.—Horizontal leaves and shoots are diaheliotropic as well as diageolropic. The general direction IRRITABILITY. 85 which leaves assume under this influence is that of placing them with the upper surface perpendicular to the rays of light which fall upon them. Leaves, then, exposed to the brightly lighted sky are, in general, horizontal. This position is taken in direct response to the stimulus of light. The leaves of plants with a one-sided illu- mination, as can be seen by trial, are turned with Fig. 73- thei 4 a nelr u r Seedling of castor-oil bean, before and after PPS a one-sided illumination. surfaces to- ward the source of light, or perpendicular to the in- cidence of the light rays. In this way light overcomes for the time being the direction which growth gives to the leaves. The so-called ‘‘sleep’’ of plants is of course not sleep, though the leaves ‘‘ nod,”’ or hang downward, in many cases. There — are many plants in which we can note this drooping of the leaves at nightfall, and in order to prove that it is not determined by the time of day we can resort to a well-known ex- periment to induce this condition dur- ing the day. The plant which has been used to illus- trate this is the sun- flower. Some of these plants, which Fig. 74. Dark chamber with opening at one side to show heliotropism, (After Schleichert.) 86 PH VSIOLOG Y. were grown in a box, when they were about 35cm high were covered for nearly two days, so that the light was excluded. At midday on the second day the box was removed, and the leaves on the covered plants are well represented by fig. 75, which was made from one of them. The leaves of the other plants in the box which were not covered were horizontal, as shown by fig. 76. Now on leaving these plants, which had exhibited Vig. 75. Sunflower plant. Epinastic con- dition of leaves induced durmg the day in darkness. Hf Fig. 76. Sunflower plant removed from darkness, leaves extending under influence of light (diaheliotro- pism.) induced ‘‘sleep’’ move- ments, exposed to the light they gradually assumed the horizontal position again. 202. Epinasty and hyponasty.—During the carly stages of growth of many leaves, as in the sunflower plant, the direction of growth is different from what it is at a later period. The under surface of the young Jeaves grows more rapidly in a longitudinal direction than the upper side, so that the leaves are held upward close against the bud at the end of the stem. This is termed Ayponasty, or the leaves are said to be Ayponastic. Later the growth is more rapid on the upper side and the leaves turn downward or away from the bud. This is termed ef7zasty, or the leaves are said to be epivastic. This is shown by the night position of the leaves, or in the induced ‘‘sleep”’ of the sun- IRRITABILITY, 87 flower plant in the experiment detailed above. The day position of the leaves on the other hand, which is more or less horizontal, is induced because of their irritability under the influence of light, the inherent downward or epinastic growth is overcome for the time. Then at nightfall or in darkness, the stimulus of light being removed, the leaves assume the position induced by the direction of growth. In the case of the cotyledons of some plants it would seem that the growth was hyponastic even after they have opened. The day position of the coty- Fig. 77- Fig. 78. Squash seedling. Position of cotyledons in Squash seedling. Position of cotyledons in light. the dark. ledons of the pumpkin is more or less horizontal, as shown in fig. 77. At night, or if we darken the plant by covering with a tight box, the leaves assume the position shown in fig. 78. While the horizontal position is the general one which is assumed by plants under the influence of light, their position is dependent to a certain extent on the intensity of the light as well as on the incidence of the light rays. Some plants are so strongly heliotropic that they change their posi- tions all during the day. 203. Leaves with a fixed diurnal position.—Leaves of some plants when they are developed have a fixed diurnal position and are not subject to 88 PHYSIOLOGY. variation. Such leaves tend to arrange themselves in a vertical or para- heliotropic position, in which the surfaces are not exposed to the incidence of light of the greatest intensity, but to the incidence of the rays of diffused light. Interesting cases of the fixed position of leaves are found in the so- called compass plants (like Silphium laciniatum, Lactuca scariola, etc.). In these the horizontal leaves arrange themselves with the surfaces vertical, and also pointing north and south, so that the surfaces face east and west. 204. Importance of these movements.—Not only are the leaves placed in a position favorable for the absorption of the rays of light which are con- cerned in making carbon available for food, but they derive other forms of energy from the light, as heat, which is absorbed during the day. Then with the nocturnal position, the leaves being drooped down toward the stem, or with the margin toward the sky, or with the cotyledons as in the pump- kin, castor-oil bean, etc., clasped upward together, the loss of heat by radiation is less than it would be if the upper surfaces of the leaves were exposed to the sky. 205. Influence of light on the structure of the leaf.—In our study of the structure of a leaf we found that in the ivy leaf the palisade cells were on the upper surface. This is the case with a @,, great many leaves, and is the normal arrange- ment of ‘dorsiventral’’ leaves which are dia- heliotropic. Leaves which are paraheliotropic tend to have palisade cells on both surfaces. The palisade layer of cells: as we have seen is made up of cells lying very close together, and they thus prevent rapid evaporation. They also check to some extent the entrance of the rays of light, at least more so than the loose spongy parenchyma cells do. Leaves developed in the shade have looser palisade and paren- chyma cells. In the case of some plants, if we turn over a very young leaf, so that the under side will be uppermost, this side will develop the palisade layer. This shows that light has a great influence on the structure of the leaf. 206. Movement influenced by contact.—In the case of tendrils, twining leaves, or stems, the irritability to contact is shown in a move- Fig. 79. ment of the tendril, ete., toward the object in Coiling tendril of bryony. touch. This causes the tendril or stem to coil around the object for support. The stimulus is also extended down the part of the tendril below the point of contact (sec fig. 79), and that part coils IRRITABILIT Y. 89 up like a wire coil spring, thus drawing the leaf or branch from which the tendril grows closer to the object of support. This coil between the object of support and the plant is also very important in casing up the plant when subject to violent gusts of wind which might tcar the plant from its support were it not for the yielding and springing motion of this coil. 207. Sensitive plants.—These plants are remarkable for the rapid response to stimuli. Mimosa pudica is an excellent plant to study for this purpose. 208. Movement in response to stimuli.—If we pinch with the forceps one of the terminal leaflets, or tap it with a pencil, the two end leaflets fold above the ‘‘ vein’’ of the pinna. This : is immediately followed by the movement of the next pair, and so on as shown in fig. 81, until all the leaflets on this pinna are closed, then the stimu- lus travels down the other pinne in a simi- Jar manner, and Sensitive-plant leaf in normal position. Fig. 81. Pinne fold- ing up after stimulus. soon the pinne approximate each other and the leaf then drops downward as shown in Fig. $2. : Later aJl the pinne fig. 82. “Ihe normal position of the leaf 1s teed and lest drooped. shown in fig. 80. If we jar the plant by striking it or by jarring the pot in which it is grown all the leaves quickly collapse into the position shown in fig. 82. If we examine the leaf now we see minute cushions at the base of each leaflet, at the junction of the pinne with the petiole, and a larger one at the junction of the petiole with the stem. We shall also note that the move- ment resides in these cushions. go PHYSIOLOGY. 209. Transmission of the stimulus.—The transmission of the stimulus in this mimosa from one part of the plant has been found to be along the cells of the bast. 210, Cause of the movement.—The movement is caused by a sudden loss of turgidity on the part of the cells in one portion of the pulvinus, as the cushion is called. In the case of the large pulvinus at the base of the petiole this loss of turgidity is in the cells of the lower surface. There is a sudden change in the condition of the protoplasm of the cells here so that they lose a large part of their water. This can be seenif with asharp knife we cut off the petiole just above the pulvinus before move- ment takes place. A drop of liquid exudes from the cells of the lower side. 211. Paraheliotropism of the leaves of the sensitive plant.—If the mimosa plant is placed in very intense light the leaflets will turn their edges toward the incidence of the rays of light. This is also true of other plants in intense light, and is paraheliotropism. Transpiration is thus lessened, and chlorophyll is protected from too intense light. We thus see that variations in the intensity of light have an important influence in modifying movements. Variations in temperature also exert a considerable influence, rapid Pry / yt elevation of temperature causing | 7 certain flowers to open, and ~ falling temperature causing N them to close. 212. Sensitiveness of insec- tivorous plants. — The Venus fly-trap (Dionzea muscipula)and the sundew (drosera) are in- teresting examples of sensitive plants, since the leaves close in response to the stimulus from Fig. 83. Wig. S4 insects. Leaf_of Venus fly- Leaf of Drosera ro- trap (Dionaa musci- tundifolia, some of the pula), showing winged Jandular hairs foldi 7 etiole and toothed weed as a result OFS 213. Hydrotropism at obes. stimulus, Roots are sensitive to mois- ture. They will turn toward moisture. This is of the greatest importance for the well-being of the plant, since the roots will seek those places in the soil where suitable moisture is present. On IRRITABILITY. gl the other hand, if the soil is too wet there is a tendency for the roots to grow away from the soil which is saturated with water. In such cases roots are often seen growing upon the surface of the soil so that they may obtain oxygen, which is important for the root in the processes of absorption and growth. Plants then may be injured by an excess of water as well as by a lack of water in the soil. 214. Temperature.—In the experiments on germination thus far made it has probably been noted that the temperature has much to do with the length of time taken for seeds to germinate. It also influences the rate of growth. The effect of different temperatures on the germination of seed can be very well noted by attempting to germinate some in rooms at various temperatures. It will be found, other conditions being equal, that in a moderately warm room, or even in one quite warm, 25-30 degrees cen- tigrade, germination and growth goes on more rapidly than in a cool room, and here more rapidly than in one which is decidedly cold. In the case of most plants in temperate climates, growth may go on at a temperature but little above freezing, but few will thrive at this temperature. 215. If we place dry peas or beans ina temperature of about 70° C. for 15 minutes they will not be killed, but if they have been thoroughly soaked in water and then placed at this temperature they will be killed, or even at a somewhat lower temperature. The same seeds in the dry condition will withstand a temperature of 10° C. below, but if they are fest soaked in water this low temperature will kill them. . 216. In order to see the effect of freezing we may thoroughly freeze a sec- tion of a beet root, and after thawing it out place it in water. The water is colored by the cell-sap which escapes from the cells, just as we have seen it does as a result of a high temperature, while a section of an unfrozen beet placed in water will not color it if it was previously washed. If the slice of the beet is placed at about — 6° C, ina shallow glass vessel, and covered, ice will be formed over the surface. If we examine it with the microscope ice crystals will be seen formed on the outside, and these will not be colored. The water for the formation of the crystals came from the cell-sap, but the concentrated solutions in the sap were not withdrawn by the freezing over the surface. / 217. If too much water is not withdrawn from the cells of many plants in freezing, and they are thawed out slowly, the water which was withdrawn from the cells will be absorbed again and the plant will not be killed. But if the plant is thawed out quickly the water will not be absorbed, but will remain on the surface and evaporate. Some will also remain in the inter- cellular spaces, and the plant will die. Some plants, however, no matter how 92 PHYSIOLOGY. slowly they are thawed out, are killed after freezing, as the leaves of the pumpkin, dahlia, or the tubers of the potato. 218. It has been found that as a general rule when plants, or plant parts,. contain little moisture they will withstand quite high degrees of tempera- ture, as well as quite low degrees, but when the parts are filled with sap or water they are much more easily killed. For this reason dry seeds and the winter buds of trees, and other plants, because they contain but little water, are better able to resist the cold of winters. But when growth begins in the spring, and the tissues of these same parts become turgid and filled with water, they are quite easily killed by frosts. It should be borne in mind, however, that there is great individual variation in plants in this respect, some being more susceptible to cold than others. There is also great varia- tion in plants as to their resistance to the cold of winters, and of arctic climates, the plants of the latter regions being able to resist very low tem- peratures. We have examples also in the arctic plants, and those which grow in arctic climates on high mountains, of plants which are able to carry on all the life functions at temperatures but little above freezing. : MORPHOLOGY AND LIFE HISTORY OF REPRE- SENTATIVE PLANTS. CHAPTER XV. SPIROGYRA, 219. In our study of protoplasm and some of the processes of plant life we became acquainted with the general appearance of the plant spirogyra. It is now a familiar object to us. And in taking up the study of representative plants of the different ~ groups, we shall find that in knowing some of these lower plants the difficulties of understanding methods of reproduction and relationship are not so great as they would be if we were entire- ly ignorant of any members of the lower groups. 220. Form of spirogyra.—We have found that the plant spirogyra consists of simple threads, with cylindrical cells attached end to end. We have also noted that each cell of the thread is exactly alike, with the exception of certain ‘‘ hold- fasts’’ on some of the species. If we should examine threads in different stages of growth we should find that each cell is capable of growth and division, just as it is capable of performing all the functions of nutrition and assimilation. The cells of spirogyra then multiply by division. Not simply the cells at the ends of the threads but any and all of the cells divide as they grow, and in this way the threads increase in length. _ 221. Multiplication of the threads.—In studying living material of this . plant we have probably noted that the threads often become broken by two of the adjacent cells of a thread becoming separated. This may be and is accom- . 93 94. MORPHOLOGY. plished in many cases without any injury to the cells. In this manner the Fig. 85. Thread of spiro- gyra, showing lon, cells, chlaraphyil band, nucleus, strands of proto- plasm, and_ the granular wall layer of protoplasm. threads or plants of spirogyra, if we choose to calla threada plant, multiply, or increase. In this breaking ofa thread the cell wall which separates any two cells splits. If we should examine several species of spirogyra we would probably find threads which present two types as regards the character of the walls at the ends of the cells. In fig. 85 we see that the ends are plain, that is, the cross walls are all straight. But in some other species the inner wall of the cells presents a peculiar appearance. This inner wall at the end of the cell is at first straight across. But it soon becomes folded back into the interior of its cell, just as the end of an empty glove finger may be pushed in. Then the infolded end is pushed partly out again, so that a peculiar figure is the result. 222. How some ot the threads break.—In the separation of the cells of a thread this peculiarity is often of advan- tage to the plant. The cell-sap within the protoplasmic membrane absorbs water and the pressure pushes on the ends of the infolded cell walls. The inner wall being so much longer than the outer wall, a pull is exerted on the latter at the junction of the cells. Being weaker at this point the outer wall is ruptured. The turgidity of the two cells causes these infolded inner walls to push out suddenly as the outer wall is ruptured, and the thread is snapped apart as quickly as a pipe-stem may be broken. 223. Conjugation of spirogyra.—Under cer- tain conditions, when vegetative growth and multiplication cease, a process of reproduction takes place which is of a kind termed sexual repro- duction. If we select mats of spirogyra which have lost their deep green color, we are likely to find different stages of this sexual process, which in the case of spirogyra and related plants is called conjugation. A few threads of such a mat we should examine with the microscope. If the material is in the right condition we see in certain of the cells an oval or elliptical body. If we note carefully the cells in which these oval bodies are situated, there will be seen a tube at one side which con- SPIROG YRA. 95 nects with an empty cell ofa thread which lies near as shown in fig. 86. Ifwesearch through the material we may see other threads connected in this ladder fashion, in which the contents of the cells are in various stages of collapse from what we have seen in the growing cell. In some the protoplasm and chlorophyll band have moved but little from the wall; in others it forms a mass near the center of the cell, and again in others we will see that the contents of the cell of one of the threads has moved partly through the tube into the cell of the thread with which it is connected. 224. This suggests to us that the oval bodies found in the cells of one thread of the ladder, while the cells of the other thread were empty, are formed by the union of the contents of the two cells. In fact that is what does take place. This kind of union of the contents of two similar or nearly similar cells is conjugation. The oval bodies which are the result of this conjugation are zygo/es, or zygospores. When we are examining living ma- terial of spirogyra in this stage it is possible to watch this process of con- jugation. Fig. 87 represents the differ- Fig. 86. ent stages of conjugation of spirogyra. Zygospores of spirogyra. 225. How the threads conjugate, or join.—The cells of two threads lying parallel put out short processes. The tubes from two opposite cells meet and join. The walls separating the con- tents of the two tubes dissolve so that there is an open communi- cation between the two cells. The content of each one of these cells which take part in the conjugation is a gamefe. The one which passes through the tube to the receiving cell is the supply- 96 MORPHOLOGY. mg gamete, while that of the receiving cell is the recemng gamete. 226. How the protoplasm moves from one cell to another.—Before any movement of the protoplasm of the supplying cell takes place we can see Vig. 87. Conjugation in spirogyra; from left to right beginning in the upper row is shown the gradual passage of the protoplasm from the supplying gamete to the receiving gamete. that there is great activity in its protoplasm. Rounded vacuoles appear which increase in size, are filled with a watery fluid, and swell up like a vesicle, and then suddenly contract and disappear. As the vacuole disap- pears it causes a sudden movement or contraction of the protoplasm around it to take its place. Simultaneously with the disappearance of the vacuole the membrane of the protoplasm is separated from a part of the wall. This is probably brought about by a sudden loss of some of the water in the cell- sap. These activities go on, and the protoplasmic membrane continues to slip away from the wall. Every now and then there is a movement by which the protoplasm is moved a short distance. It is moved toward the tube and finally a portion of it with one end of the chlorophyll band begins to move into the tube. About this time the vacuoles can be seen in an active condition in the receptive cell. At short intervals movement con- SPIROG YRA. 97 tinues until the content of the supplying cell has passed over into that of the receptive cell. The protoplasm of this one is now slipping away from the cell wall, until finally the two masses round up into the one zygospore. 227. The zygospore.—This zygospore now acquires a thick wall which eventually becomes brown in color. The chlorophyll color fades out, and a large part of the protoplasm passes intv an oily substance which makes it more resistant to conditions which would be fatal to the vegetative threads. The zygospores ure capable therefore of enduring extremes of cold and dry- ness which would destroy the threads. They pass through a ‘resting ” period, in which the water in the pond may be frozen, or dried, and with the oncoming of favorable conditions for growth in the spring or in the autumn they germinate and produce the green thread again. 228. Life cycle.—The growth of the spirogyra thread, the conjugation of the gametes and formation of the zygospore, and the growth of the thread from the zygospore again, makes what is called a complete Ze cycle. 229. Fertilization.—While conjugation results in the fusion of the two masses of protoplasm, fertilization is accomplished when the nuclei of the two cells come together in the zygospore and fuse into a single nucleus. The Fig. 88. Fertilization in spirogyra ; shows different stages of fusion of the two nuclei, with mature zygospore at right. (After Overton.) different stages in the fusion of the two nuclei of a recently formed zygospore are shown in figure 88. In the conjugation of the two cells, the chlorophyll band of the supplying cell is said to degenerate, so that in the new plant the number of chlorophyll bands in a cell is not increased by the union of the two cells. 230. Simplicity of the process.—In spirogyra any cell of the thread may form a gamete (excepting the holdfasts of some species). Since all of the cells of a thread are practically alike, there is no structural difference between a vegetative cell andacell about to conjugate. ‘The difference is a physiological one. All the cells are capable of conjugation if the physiolog- ical conditions are present. All the cells therefure are potential gametes. (Strictly speaking the wall of the cell is the gametangium, while the content forms the gamete.) While there is sometimes a slight difference in size between the conjugat- 98 MORPHOLOGY. ing cells, and the supplying cell may be the smaller, this isnot general. We say, therefore, that there is no differentiation among the gametes, so that usually before the protoplasm begins to move one cannot say which is to be the supplying and which the receiving gamete. 231. Position of the plant spirogyra.—From our study then we see that there is practically no differentiation among the vegetative cells, except where holdfasts grow out from some of the cells for support. They are all alike in form, in capacity for growth, division, or multiplication of the threads. Each cell is practically an independent plant. There is no differ- entiation between vegetative cell and conjugating cell. All the cells are potential gametes. Finally there is no structural differentiation between the gametes. This indicates then a simple condition of things, a low grade of organization. 232. The alga spirogyra is one of the representatives of the lower alga belonging to the group called Conjugate. Zygnema with star-shaped chloro- plasts, mougeotia with straight or sometimes twisted chlorophyll bands, be- long to the same group. In the latter genus only a portion of the protoplasm of each cell unites to form the zygospore, which is located in the tube between the cells. Fig. gt. . Xanthidium. Fig. go. Micrasterias. Fig. 89. Fig. 92. Fig. 94. Closterium. Staurastrum, Euvastrum. Cosmarium. 233. The desmids also belong tothe same group. The desmids usually live as separate cells. Many of them are beautiful in form. They grow entangled among other algee, or on the surface of aquatic plants, or on wet soil. Sev- eral genera are illustrated in figures 89-94. CHAPTER XVI. CEDOGONIUM. 234. Cdogonium is also an alga. The plant is sometimes associated with spirogyra, and occurs in similar situations. Our attention was called to it in the study of chlorophyll bodies. These we recollect are, in this plant, small oval disks, and thus differ from those in spirogyra. 235. Form of cedogonium.—Like spirogyra, cedogonium forms simple threads which are made up-of cylindrical cells placed end to end. But the plant is very different from any member of the group to which spirogyra belongs. In the first place each cell is not the equivalent of an individual plant as in spirogyra. Growth is localized or confined to certain cells of the thread which divide at one end in such a way as to leave a peculiar overlapping of the cell walls in the form of a series of shallow caps or vessels (fig. 95), and this is one of the character- istics of this genus. Other differences we find in the manner of reproduction. 236. Fruiting stage of edogonium.—Material in the fruiting stage is quite easily obtainable, and may be preserved for study in formalin if there is any doubt about obtaining it at the time we need it for study. This condition of the plant is easily de- tected because of the swollen condition of some of the cells, or by the presence of brown bodies with a thick wall in some of the cells. 237. Sexual organs of edogonium. Oogonium and egg.— The enlarged cell is the oogonium, the wall of the cell being the wall of tne oogonium. (See fig.96.) The protoplasm inside, before 99 100 MORPHOLOGY. fertilization, istheegg cell. In those cases where the brown body with a thick wall is present fertilization has taken place, and this body is the fertilized egg, or oospore. It contains large quantities of an oily substance, and, like Fig. 95. Portion of thread of cedo- gonium, show- ing chlorophyll grains, and pe- culiar cap cell Fig. 96. walls. (Edogonium undulatum, with oogonia and dwarf males; the upper oogonium at the right has a mature oospore. the fertilized egg of spirogyra and vaucheria, is able to with- stand greater changes in temperature than the vegetative stage, and can endure drying and freezing for some time without injury. In the oogonium wall there can frequently be seen a rift near the middle of one side, or near the upper end. This is the EDOGONIUAM. IOI opening through which the spermatozoid entered to fecundate the egg. 238. Dwarf male plants.—In some species there will also be seen peculiar club-shaped dwarf plants attached to the side of the oogonium, or near it, and in many cases the end of this dwarf plant has an open lid on the end. 239. Antheridium.—The end cell of the dwarf male in such species is the antheridium. In other species the spermatozoids are developed in different cells (antheridia) of the same thread which bears the oogonium, or on a different thread. 240. Zoospore stage of ceedogonium.—The egg after a period of rest starts into active life again. In doing so it does not develop the thread-like plant directly as in the case of vaucheria and spirogyra. It first divides into four zoospores which are exactly like the zoogonidia in form. (See fig. 103.) These germinate and develop the thread form again. This is a quite re- markable peculiarity of cedogonium when compared with either vaucheria or spirogyra. It is the introduction of an intermediate stage between the fertilized egg and that form of the plant which bears the sexual organs, and should be kept well in mind. 241. Asexual reproduction.—Material for the study of this stage of cedo- gonium is not readily obtainable just when we wish it for study. But fresh plants brought in and placed ina quantity of fresh water may yield suitable material, and it should be fee examined at intervals for several Shy days. This kind of reproduction takes place by the formation of soogonidia. The entire contents of a cell round off into an oval body, the wall of the cell breaks, Fig. 97. Zoogonidia of ceedogonium escaping. and the zoogonidium escapes. It At the right one is germinating and forming the holdfasts, by means of which has a clear Space: at the small these alge attach themselves to objects end, and around this clear space for support. (After Pringsheim.) is a row or crown of cilia as shown in fig. 97. By the vibration of these cilia the zoogonidium swims around for a time, then settles down on some object of support, and several slender holdfasts grow out in the form of short rhizoids which attach the young plant. 242. Sexual reproduction. Antheridia.—The antheridia are short cells which are formed by one of the ordinary cells dividing into a number of disk-shaped ones as shown in fig. 98. The protoplasm in each antheridium 102 MORPHOLOGY. forms two spermatozoids (sometimes only one) which are of the same form as the zoogonidia but smaller, and yeilowish instead of green. In some species a motile body intermedi- ate in size and color be- tween the spermatozoids and zoogonidia is first formed, which after swimming around comes to rest on the oogonium, or near it, and develops what is called a ‘‘ dwarf male plant” from which the real spermatozoid is produced. Fig, 98. Fig. 99. . Portion of thread Portion of thread of cedo- oa8: Gogunis. ane of cdogonium gonium showing upper half oogonia are formed di- showing antheridia of egg open, and a sperma- tozoid ready to enter. (After rectly from one of the Oltmans). vegetative cells. In most species this cell first enlarges in diameter, so that it is easily detected. The protoplasm inside is the egg cell. The oogonium wall opens, a bit of the protoplasm is emitted, and the spermatozoid then enters and fertilizes it (fig. 99). Nowa hard brown wall is formed around it, and, just as in spirogyra Fig 100. Fig. ror. Fig. 102. Male nucleus just entering Male nucleus fusing with The two nuclei fused, and egg at left side. female nucleus. fertilization complete. Figs. 100-102.—Fertilization in cedogonium. (After Oltmans). and vaucheria, it passes through a resting period. Atthe time of germination it does not produce the thread-like plant again directly, but first forms four zoospores exactly like the zoogonidia (fig. 103). These zoospores then germinate and form the plant. 244. (Edogonium compared with spirogyra.—Now if we compare cedo- gonium with spirogyra, as we did in the case of vaucheria, we find here also that there is an advance upon the simple condition which exists in spiro- gyra. Growth and division of the thread is limited to certain portions. The sexual organs are differentiated. They usually differ in form and size from the vegetative cells, though the oogonium is simply a changed vegetative @DOGONIUM. 103 cell. The sexual organs are differentiated among themselves, the antheridium is small, and the oogonium large. The gametes are also differentiated in size, and the male gamete is motile, and carries in its body the nucleus which fuses with the nucleus of the egg cell. But a more striking advance is the fact that the fertilized egg does not Fig. 103. Fertilized egg of cedogonium after a period of rest escaping from the wall of the oogonium, and dividing into the four zoospores. (After Juranyi.) produce the vegetative thread of cedogonium directly, but first forms four zoospores, each of which is then capable of developing into the thread. On the other hand we found that inspirogyra the zygo- spore develops directly into the thread form of the plant. 245. Position of cdo- gonium.—(Edogonium is one of the true thread-like algze, green in color, and the threads are divided Fig. 104. into distinct cells. It, Tuft of cheto- - phora, natural along with many relatives, size. was once placed in the old genus conferva. These are all now placed in the group Confervoidee, that is, the conferva-like alge. Fig. 105. 246. Relatives of edogonium.—Muany other genera Portion of chetophora are related to cedogonium. Some consist of simple ‘OS branching. threads, and others of branched threads. An example of the branched forms is found in chetophora, represented in figures 104, 105. This plant grows in quiet pools or in slow-running water. It is attached to sticks, rocks, or to larger aquatic plants. Many threads spring from the same point of attachment and radiate in all directions. This. together with the branching of the threads, makes a small, compact, greenish, rounded mass, which is 104. MORPHOLOGY. held firmly together by a gelatinous substance. The masses in this species are about the size of a small pea, or smaller. Growth takes place in che- tophora at the ends of the threads and branches. That is, growth is api- cal. This, together with the branched threads and the tendency to form cell masses, is a great advance of the vegetative condition of the plant upon that which we find in the simple threads of cedogonium. CHAPTER XVII. VAUCHERIA. 247. The plant vaucheria we remember from our study in an earlier chapter. It usually occurs in dense mats floating on the water or lying on damp soil. The texture and feeling of these mats remind one of ‘‘felt,’’ and the species are sometimes called the ‘‘ green felts.’’ The branched threads are continuous, that is there are no cross walls in the vegetative threads. This plant multiplies it- self in several ways which would be too tedious to detail here. But when fresh bright green mats can be obtained they should be placed in a large vessel of water and set in a cool place. Only asmall amount of the alga should be placed in a vessel, since decay will set in more rapidly with a large quantity. For several days one should look for small green bodies which may be floating at the side of the vessel next the lighted window. Fig. 106. Portion of branched thread of vaucheria. 248. Zoogonidia of vaucheria.—If these minute floating green bodies are found, a small drop of water containing them should be mounted for exami- 105 106 MORPHOLOGY. nation. If they are rounded, with slender hair-like appendages over the surface, which vibrate and cause motion, they very likely are one of the kinds of reproductive bodies of vaucheria. The hair-like appendages are cilia, and they occur in pairs, several of them distributed over the surface. These rounded bodies are gontdia, and because they are motile they are called zoogonidia. By examining some of the threads in the vessel where they occurred we may have perhaps an opportunity to see how they are produced. Short branches are formed on the threads, and the contents are separated from those of the main thread by a septum. The protoplasm and other contents of this branch separate from the wall, round up into a mass, and escape through an opening which is formed in the end. Here they swim around in the water for a time, then come to rest, and germinate by growing out into a tube which forms another vaucheria plant. It will be observed that this kind of reproduction is not the result of the union of two different parts of the plant. It thus differs from that which is termed sexual reproduction. A small part of the plant simply becomes separated from it as a special body, and then grows into a new plant. a sort of multiplication. This kind of re- production has been termed asexual reproduction. 249. Sexual reproduction in vaucheria.—The organs which are concerned in sexual reproduction in vaucheria are very readily obtained for study if one collects the material at the right season. They are found quite readily during the spring and autumn, and may be preserved in formalin for study at any season, if the material cannot be collected fresh at the time it is desired for study. Fine material for study often occurs on the soil of pots in greenhouses during the winter. While the zoogonidia are more apt to be found in material which is quite green and fresh- ly growing, the sexual organs are usually more abundant when the threads appear some- what yellowish, or yellow green. 250. Vaucheria sessi- lis; the sessile vauche- Young antheridium and oogonium of Vaucheria ses- silis, before separation from contents of thread by a ria.—In this plant the septum, lig. 107. sexual organs are sessile, that is they are not borne ona stalk as in some other species. The sexual organs usually occur several ina group. Fig. 107 represents a portion of a fruiting plant. ee VAUCHERTA. 107 251. Sexual organs of vaucheria. Antheridium.—The antheridia are short, slender, curved branches from a main thread. A septum is formed which separates an end portion from the stalk, This end cell is the antheridium. Frequently it is collapsed or empty as shown in fig. 108. The protoplasm in Fig 108. Vaucheria sessilis, one antheridium between two oogonia. the antheridium forms numerous small oval bodies each with two slender lashes, the cilia. When these are formed the antherid- ium opens at the end and they escape. It is after the escape of these spermatozoids that the antheridium is collapsed. Each spermatozoid is a male gamete. 252. Oogonium.—The oogonia are short branches also, but they become large and somewhat oval. The septum which separates the protoplasm from that of the main thread is as we see near the junction of the branch with the main Fig. 109. Vaucheria sessilis; oogonium opening and emit- i 7 ting a bit of protoplasm; spermatozoids; sperma- as shown in the figure, 18 tozoids entering oogonium. (After Pringsheim and usually turned somewhat Goebel.) thread. The oogonium, to one side. When mature the pointed end opens and a bit of the protoplasm escapes. The remaining protoplasm forms the large rounded egg cell which fills the wall of the oogonium, In some of the oogonia which we examine this egg is surrounded by a thick brown wall, with starchy and oily contents. This is the 108 MORPHOLOGY. fertilized egg (sometimes called here the oospore). It is freed from the oogonium by the disintegration of the latter, sinks into Vig. 110. Fertilization in vaucheria. 77, male nucleus ;_/7, female nucleus. Male nucleus entering the egg and approaching the female nucleus. (After Oltmans.) the mud, and remains here until the following autumn or spring, when it grows directly into a new plant. 253. Fertilization.—Fertilization is accomplished by the spermatozoids swimming in at the open end of the oogonium, Fertilization of vaucheria. /1, female nucleus; #2”, male nucleus. The different figures show various stages in the fusion of the nuclei. when one of them makes its way down into the egg and fuses with the nucleus of the egg. 254. The twin vaucheria (V. geminata).—Another specics of vaucheria is the twin vaucheria. This is also a common one, and may be used for study instead of the sessile vaucheria if the latter cannot be obtained. The sexual organs are borne at the end of a club-shaped branch. ‘There are usually two oogonia, and one antheridium between them which terminates the branch. In a closely related species, instead of the two oogonia there is a whorl of them with the antheridium in the center. 255. Vaucheria compared with spirogyra.—In vaucheria we have a plant which is very interesting to compare with spirogyra in several respects. VAUCHERIA,. 109 Growth takes place, not in all parts of the thread, but is localized at the ends of the thread and its branches. This represents a distinct advance on such a plant as spirogyra. Again, only specialized parts of the plant in vaucheria form the sexual organs. These are short branches. Farther there is a great difference in the size of the two organs, and especially in the size of the gametes, the supplying gametes (spermatozoids) being very minute, while the receptive gamete is large and contains all the nutriment for the fertilized egg. In spirogyra, on the other hand, there is usually no differ- ence in size of the gametes, as we hive seen, and each contributes equally in the matter of nutriment for the fertilized egg. Vaucheria, therefore, rep- resents a distinct advance, not only in the vegetative condition of the plant, but in the specialization of the sexual organs. Vaucheria, with other related algze, belongs toa group known as the Szphonea, so called because the plants are tube-like or siphon-like. CHAPTER XVIII. COLEOCHETE, 256. Among the green algz coleochete is one of the most interesting. Several species are known in this country. One of these at least should be examined if it is possible to obtain it. It occurs in the water of fresh lakes and ponds, attached to aquatic plants. 257. The shield-shaped coleochete.—This plant (C. scutata) a P Fig. 112. Stem of ass aquatic plant 3 (| showing co- \ [} leochete, natural size. Kt f x Fig. 113. Thallus of Coleochzte scutata. is in the form of a flattened, circular, green plate, as shown in fig. 112. It is attached near the center on one side to rushes IIo COLEOCHAETE. Ill and other plants, and has been found quite abundantly for sev- eral years in the waters of Cayuga Lake at its southern extremity. As will be seen it consists of a single layer of green cells which radiate from the center in branched rows to the outside, the cells lying so close together as to form a continuous plate. The plant started its growth from a single cell at the central point, and grew at the margin in all directions. Sometimes they are quite irregu- lar in outline, when they lie quite closely side by side and inter- fere with one another by pressure. If the surface is examined carefully there will be found long hairs, the base of which is en- closed in a narrow sheath. It is from this character that the genus takes its name of coleochzete (sheathed hair). 258. Fruiting stage of coleochete.—lIt is possible at some seasons of the year to find rounded masses of cells situated near the margin of this green disk. These have developed from a fertilized egg which remained attached to the plant, and prob- ably by this time the parent plant has lost its color. 259. Zoospore stage.—This mass of tissue does not develop directly into the circular green disk, but each of the cells forms a zoospore. Here then, as in cedogonium, we have an- other stage of the plant in- terpolated between the fer- tilized egg and that stage of the plant which bears the gametes. But in coleochete we have a distinct advance in this stage upon what is pres- Fiesty, of ortign of thallus = _ i Portion of thallus of Co- scutata, = showing ent in cedogonium, for in leochezte scutata, showing four antheridia ili empty cells from which formed from one coleochete the fertilized zoogonidia have escaped, thallus cell; a sin- ‘i i one fromeach cell; zoogo- __gle spermatozoidat egg develops first into a nidia at the left.’ (After the right’ (After several-celled mass of tissue Pringsheim.) Pringsheim.) before the zoospores are formed, while in cedogonium only four zoospores are formed directly from the egg. Hig 260. Asexual reproduction.—In asexual reproduction any of the green cells on the plant may form zoogonida. The contents of a cell round off and 112 MORPHOLOGY. form a single zoogonidium which has two cilia at the smaller end of the oval body, fig. 114. After swimming around for a time they come to rest, ger- minate, and produce another plant. 261. Sexual reproduction.—Oogonium.—The oogonium is formed by the enlargement of a cell at the end of one of the threads, and then the end of the Fig. 116. Coleochate soluta; at left branch bearing oogonium (cog); antheridia (ax); egg in oogonium and surrounded by enveloping threads; at center three antheridia open, and one spermatozoid ; at right sporocarp, mature egg inside sporocarp wall. cell elongates into a slender tube which opens at the end to form a channel through which the spermatozoid may pass down to the egg. The egg is formed of the contents of the cell (fig. 116). Several oogonia are formed on one plant, and in such a plant as C. scutata they are formed in a ring near the margin of the disk. 262. Antheridia.—In C. scutata certain of the cells of the plant divide into four smaller cells, and each one of these becomes an antheri- Fig. 117. Fig. 118. “ Two sporocarps \ still Sporocarp ruptured oe dium. In C, soluta the an- 1 surrounded by thallus. growth of egg to form ce Thallus finally decays and mass. Cells of ‘this sporo- - . f sets sporocarp free. phyte forming zoospores. end of terminal cells in the Figs. 117, 118, C. scutata, i form of short flasks, some- times four in number or less (fig. 116). A single spermatozoid is formed from the contents. It is oval and possesses two long cilia. After swim- theridia grow out from the COLEOCH ATE. 113 ming around it passes down the tube of the oogonium and fertilizes the egg. 263. Sporocarp.—After the egg is fertilized the cells of the threads near the egg grow up around it and form a firm covering one cell in thickness. This envelope becomes brown and hard, and serves to protect theegg. This is the ‘‘fruit”’ of the coleochete, and is sometimes called a sporocarp (spore fruit). The development of the cell mass and the zoospores from the egg has been described above: Some of the species of coleochzete consist of branched threads, while others form circular cushions several layers in thickness. These forms together with the form of our plant C. scutata make an interesting series of transi- tional forms from filamentous structures to an expanded plant body formed of a mass of cells. MORPHOLOGY. 114 x “s][29 JO ‘umr1uoSo0o spunoaims sSseW ® WLIO. speaiy} Surdojaaua oy sMmod jO [eM uoezTWe9) pure sap sayy “sdajua~ ploz qd “sjsu “umrpriey}|-oyeurszads yorya Jo “(ay Ayd “ue Ypova wo1jau0|Zuruado YBno1yy aqny *1]99 "39a ‘unipru03 sureSe aseyd “Saa|- 0, 9 we 3 ‘Ip 339)‘ proz oj eu1ads|Suoy yyM ‘[]99"3aa palapsurs wory [eIaAas 10]-ooza[SuIS v WAOF *saye[d aepno sdojaaap asods/uro ay [[emasieq fayeyioiq ‘[eAQ. |-saejua ‘wnwos0Q «=jAnoy ‘eipuayyuy jAeu [[a9 Auy -419 peduioa -00Z ‘a1odsooz/Aq papunos RITTD OM} YIM] ‘TeULseW 10/10 ‘speazyy)-azeyo Be suuoy yoeq j-ins) 33q *payenuasayiqy “payenuaiayiq: viptuosooz Aq |jeuruiay | payouerg -023[0D) “wMIppayjue “sayeul yora wo1y omy) een s® JIVMP WO saUTTaWOS “winipruos “urese aseyd “Soa “BIT LO JO uMOID|}Iq sya pue suado|"]jao aayejasaa au0|-ooza[Surs B ULIOY sdojaaap = yoy an *T[99 B8alyIIM sp1rozoy ‘Yee BANRIVFIA palwioay peLaAas ‘padeys|Avut jaa Auy “peazyy “s][22 ‘um aiodsooz surioj ‘sysoqy|adiey j|-euueds yeag |-suvyo ‘wniuos0g $|-yxstp eipuayuy |-e1p19 Jo uMOIDyO suo ly yeoupury Ao -o30pq) yova { stjao anoj}"(a@10ds00 YIM ‘erptuo3-sod urepasljo © speaiy3 OyuL sapiaiq |10) 33q “payeluarayiq. “payenuaiayiq: -00z [eAo Ag joy payuny |p jdwis suse[do} -oid jo y1q syiwa pure ‘sptoz susdo ‘youriq [eI “say suoty ‘]]B2 33a|-oyeurtads — paye -ads uo {ao papunol -ueiq [erads uo s[jao|-10d = yeutua} “sayouelq “eu ‘sysoyjasiey [-y-omyyTeMg jasaey ‘wMuos0Q § jrapusys eipuayWUY jurogy ‘s[[a9 JayiO|pue spray *snonun|-ayone a, “Apesp aseyd)-(ar0dsoo pue ‘eipuos00z|yo0 s pual-uoo ‘speaiy) ‘Baa sdojaaaq 10) 33q *payenusiagiq: *‘payenuarayiq . /BeVHow Ag jo} paywry jpayoueig “s[]Po [199 Bur “M018 |TeoLIp ups “Ay~earp aseyd *sysaq_|-e3n{uo0d Jo sjua}U09 a1} ‘aqn} Aq a}e8nluoz “speaiy} jo dn|pue aptarp jo sproit3| "e143 Boa sdopaaaq, jesodso3sZ |-uq = ‘palenuesayipuy, | 'peeatyy jo [peo kup “payenuesyipugq |suryeerq Ag js[pe2 Ty japduis -oudg “LINN ‘SHLANV) ‘SNVDUOQ TVAXaS “NOIL¥D ‘ aSVHQ SAIL ‘dadO1gAa(y SI J -11dIL70 HLMOU) | Gey anuaiere saiods sieagq NOM ORGR sae TEAR aS Ww NaOH so a8VHq =(ALAHd “STA MOH -OUOdS (e1praod pur suedi0 yenxes ay} siweq) “@] LAHAOLANV9 ‘ALW HOOTOO ‘WOINODOGD ‘VINAHONVA ‘VUADONIdS WOA ATAVL AALLVUVANOD ‘b9S CHAPTER XIX. BROWN AND RED ALG. 265. If it is desired to extend the study of the alge to other groups, especially to some of the marine forms, examples of the brown algze and of the red algee may be obtained. These are accessible at the seashore, and for inland laboratories material thay be preserved in formalin (2142). 266 The brown alge (Pheophycex).*—A good representative of one division of the brown algze and one often used for study is the genus fzcus. 267. Form and occurrence of fucus.—This plant is a more or less branched and flattened thallus or “frond.” One of them, illustrated in fig. II9g, measures I5—30c7 (6-12 inches) in length. It is attached to rocks and stones which are more or less exposed at low tide. From the base of the plant are developed several short and more or less branched expansions called ‘‘holdfasts,’’ which, as their name implies, are organs of attachment. Some species (F. vesiculosus) have vesicular swellings in the thallus. The fruiting portions are somewhat thickened as shown in the figure. Within these portions are numerous oval cavities opening by a circular pore, which gives a punctate appearance to these fruiting cushions. Tufts of hairs frequently project through them. 268. Structure of the conceptacles.—On making sections of the fruiting portions one finds the walls of the cavities covered with outgrowths. Some of these are short branches which bear a large rounded terminal sac, the oogonium, at maturity containing eight egg cells. More slender and much branched threads bear narrowly oval antheridia. In these are developed several two-ciliated spermatozoids. 269. Fertilization.—At maturity the spermatozoids and egg cells float out- side of the oval cavities where fertilization takes place. The spermatozoid sinks into the protoplasm of the egg cell, makes its way to the nucleus of the egg, and fuses with it as shown in fig. 125. The fertilized egg then grows into a new plant. Nearly all the brown algz are marine. * The members of the group possess chlorophyll, but it is obscured by a brown pigment. 115 116 MORPHOLOGY. 270. The red alge (Rhodophycex).—The larger number of the so-called red algze occur in salt water, though a few genera occur in fresh water. Fig. 121. Oogonium of fucus with ripe eggs. Fig. 119. Fig. 120. Portion of plant of fucus showing Section of conceptacle of fucus, showing conceptacles in enlarged ends; and oogonia, and tufts of antheridia. below the vesicles (Fucus vescicu- losus). (Lemanea grows only in winter in turbulent water of quite large streams. Batrachospermum grows in rather slow-running water of smaller streams. Both of these inhabit fresh water.) The plants of the group possess chloro- phyll, but it is usually obscured by a reddish or purple pigment. 271. Gracillaria.—Gracillaria is one of the marine forms, and one species is illustrated in fig. 126. It measures 15-20cvz or more long, and is pro- fusely branched in a palmate manner. The parts of the thallus are more or less flattened. The fruit is a cystocarp, which is characteristic of the rhodo- BROWN AND RED ALG. 1I7 phycex (florideze). In gracillaria these fruit bodies occur scattered over the thallus. They are somewhat flask-shaped, are partly sunk in the Fig. 122. Fig. 123. Fig. 124. Antheridia of fucus, on Antheridia of fucus with Egg of fucus surrounded branched threads. escaping spermatozoids. by spermatozoids. thallus, and the conical end projects strongly above the surface. The car- pospores are grouped in radiating threads within the oval cavity of the Fig. 125. Fertilization in fucus ;_/, female nucleus ; 7, male nucleus; 7, nucleolus. In the ieft figure the male nucleus is shown moving down through the cytoplasm of the egg; in the remaining figures the cytoplasm of the egg is omitted. (After Strasburger.) cystocarp. These cystocarps are developed as a result of fertilization. Other plants bear gonidia in groups of four, the so-called ¢etraspores. 272. Rhabdonia.—This plant is about the same size as the gracillaria, though it possesses more filiform branches. The cystocarps form prominent elevations, while the carpospores lie in separated groups around the periph- ery of a sterile tissue within the cavity. (See figs. 128, 129.) Gonidia in the form of tetraspores are also developed in rhabdonia, 118 MORPHOLOGY. Fig. 126. Fig. 127. Gracillaria, portion of frond, Gracillaria, section of cystocarp showing position of cysto- showing spores. carps. 273. The principal groups of the alge are the following: ( Protococcoidez (the protococcus (Pleurococ- cus vulgaris); the red-snow plant (Spheerella nivalis), etc. Chlorophycee. | Conjugate (spirogyra, zygnema, mougeotia, Green alge. desmids, etc.). Siphonez (vaucheria). Confervoidez (cedogonium, cheetophora, cole- l ocheete). Cyanophycee (nostoc, oscillatoria, etc.). The blue-green alge. Pheophycee (fucus, etc.). The brown algze, BROWN AND RED ALGAE. Ilg Rhodophycee (rhabdonia, gracillaria, callithamnion, champia, etc.). The red alge. 274. Some of the protococcoidez are believed to lie very near some of the lower animals like the flagellates. They are mostly single-celled plants; some of them are motile during the vegetative stage, and others are not motile, while others are Fig. 128. ‘ Rhabdonia,branched Fig. 129. - : portion of frond show- Section of cystocarp of rhabdonia, showing ing cystocarps. spores. may be obtained by scraping the red-looking matter out of the bottom of dry shallow basins in the rocks, close by fresh-water streams or lakes. es § ®, By placing some of this material in a vessel of or water for a few days the motile stage may be Figs 130. 5 Pleurococcus (pro- obtained. The protococcus, or Pleurococcus vul- tococcus) vulgaris. garis, may be obtained on the north side of trees, rocks, and walls, in damp places. . motile during certain stages. The red-snow plant a © 0 CHAPTER XX. FUNGI: MUCOR AND SAPROLEGNIA. Mucor. 275. In the chapter on growth, and in our study of proto- plasm, we have become familiar with the vegetative condition of mucor. We now wish to learn how the plant multiplies and re- produces itself. For this study we may take one of the mucors. Any one of several species willanswer. Thisplant may be grown by placing partially decayed fruits, lemons, or oranges, from which the greater part of the juice has been removed, in a moist cham- ber; or often it occurs on animal excrement when placed under similar conditions. In growing the mucor in this way we are likely to obtain Mucor mucedo, or another plant sometimes known as Mucor stolonifer, or Rhizopus nigricans, which is illus- trated in fig. 132. This latter one is sometimes very injurious to stored fruits or vegetables, especially sweet potatoes or rutaba- gas. Fig. 131 is from a photograph of this fungus on a banana. 276. Asexual reproduction.—On the decaying surface of the vegetable matter where the mucor is growing there will be seen numerous small rounded bodies borne on very slender stalks. These heads contain the gonidia, and if we sow some of them in nutrient gelatine or agar in a Petrie dish the material can be taken out very readily for examination under the microscope. Or we may place glass slips close to the growing fungus in the moist chamber, so that the fungus will develop on them, though cultures in a nutrient medium are much better. Or we may take the material directly from the substance on which it is growing. 120 FUNGI: MUCOR. 121 After mounting a small quantity of the mycelium bearing these heads, if we have been careful to take it where the heads appear quite young, it may be possible to study the early stages of their Fig. 131. 2 Portion of banana with a mould (Rhizopus nigricans) growing on one end. development. We shall probably note at once that the stalks or uptight threads which support the heads are stouter than the threads of the mycelium. These upright threads soon have formed near the end a cross wall which separates the protoplasm in the end from the remain- der. This end cell now enlarges into a vesicle of considerable size, the head as it appears, but to which is applied the name of Sporangium (sometimes called gonidangium), because it encloses the gonzdia. At the same time that this end cell is enlarging the cross wall is arching up into the interior. This forms the columella. All the protoplasm in the sporangium now divides into gonidia. These are small rounded or oval bodies. The wall of the spo- 122 MORPHOLOGY. rangium becomes dissolved, except a small collar around the stalk which remains attached below the columella (fig. 133). Fig. 132. Group of sporangia of a mucor (Rhizopus nigricans) showing rhizoids and the stolon extend- ing from an older group. By this means the gonidia are freed. These gonidia germinate and produce the mycelium again. 277. Sexual stage.—This stage is not so frequently found, but may some- times be obtained by growing the fungus on bread. Conjugation takes place in this way. Twothreads of the mycelium which lie near each other put out each a short branch which is clavate in form. The ends of these branches meet, and in each a septum is formed which cuts off a portion of the protoplasm in the end from that of the rest of the my- celium. The meeting walls of the branches now dissolve and the protoplasm of each gamete fuses into one mass. A thick wall is now formed around this mass, and the outer layer becomes rough and brown. This is the zygote or zygospore. ‘The mycelium dies and it becomes free often with the suspensors, as the stalks of these sexual branches are called, still attached. This zygo- spore passes through a period of rest, when with the entrance of favorable conditions of growth it germinatcs, and usually produces directly a sporan- gium with gonidia. This completes the normal life cycle of the plant. 278. Gemme.—Gemme, as they are somctimes called, are often formed on the mycelium. one of atwisted rope. These Ge) are very long cells from the inner part of the spore-case, and their walls are marked by spi- ral thickenings. This causes them in drying,and also when they absorb Fi G Fig. 183. moisture, to twist Elater and spore of marchantia. sf, spore; sec, mother-cell of ‘ spores, showi rtly formed : and curl in all? aaa aac sorts of ways. ‘They thus aid in pushing the spores out of the capsule as it is drying. 322. Sporophyte of marchantia compared with riccia.— We must recollect that the sporogonium in marchantia is larger than in riccia, and that it is also not lying in the tissue of the thallus, but is only attached to it at one side by a slender stalk. LIVERWORTS.: MARCHANTTA. ISI This shows us an increase in the size and complex structure of this new phase of the plant, the sfurophyfe. This is one of the very interesting things which we have to note as we go on in the study of the higher plants. Fig. 184. Marchantia polymorpha, archegonium at the left with egg: archegonium at the right with young sporogonium ; /, curtain which hangs down around the archegonia ; e, egg; v, venter of archegonium ; z, neck of archegonium; sf, young spo1ogonium. 323. Sporophyte dependent on the gametophyte for its nutri- ment.—We thussee that at no time during the development of the sporogonium is it independent from the gametophyte. This new phase of plants then, the sporophyte, has not yet become an in- dependent plant, but must rely on the earlier phase for sustenance. 824. Development of the sporogonium.—It will be interesting to note briefly how the development of the marchantia sporogonium differs from that of riccia. The first division of the fertilized egg is the same as in riccia, that is a wall which runs crosswise of the axis of the archegonium divides it into two cells. In marchantia the cell at the base develops the stalk, so that here there is a radical difference. The outer cell forms the capsule. But here after the wall is formed the inner tissue does not all go to make spores, as is the case with riccia. But some of it forms the elaters. While in riccia only the outside layer of cells of the sporogonium remained sterile, in marchantia the basal half of the egg remains completely sterile and 152 MORPHOLOG Y. develops the stalk, ana in the outer half the part which is formed from some of the inner tissue is also sterile. SOT OS o Se 23 Fig. 185. Section of developing sporogonia of marchantia; 7, nutritive tissue of gametophyte; s¢, sterile tissue of sporophyte; sf, fertile part of sporophyte; va, enlarged venter of arche- gonium. 325. Embryo.—In the development of the embryo we can see all the way through this division line between the basal half, which is completely sterile, and the outer half, which is the fertile part. In fig. 185 we see a young embryo, and it is nearly circular in section although it is composed of numerous cells. The basal half is attached to the base of the inner surface of the archegonium, and at this time the archegonium still surrounds it. The archegonium continues to grow then as the embryo grows, and we can see the remains of the shrivelled neck. The portion of the embryo attached to the base of the archegonium is the sterile part and is called the ‘ foot,” and later develops the stalk. The sporogonium during all the stages of its development derives its nourishment from the gametophyte at this point of LIVERWORTS: MARCHANTIA. 153 attachment at the base of the archegonium. Soon, as shown in fig. 185 at the right, the outer portion of the sporogonium begins to differentiate into the cells which form the elaters and those which form spores. These lie in radiating lines side by side, and form what is termed the archesporium. Each fertile cell forms four spores just as in riccia. They are thus called the mother cells of the spores, or spore mother cells. 3826. How marchantia multiplies.—New plants of marchantia are formed by the germination of the spores, and growth of the same to the thallus. The plants may also be multiplied by parts of the old ones breaking away by the action of strong currents of water, and when they lodge in suitable places grow into well-formed plants. As the thallus lives from year to year and continues to grow and branch the older portions die off, and thus sepa- rate plants may be formed from a former single one. 327. Buds, or gemme, of marchantia.—But there is another way in which marchantia multiplies itself. If we examine the upper surface of such a Fig. 186. Marchantia plant with cupules and gemmz ; rhizoids below. plant as that shown in fig. 186, we shall see that there are minute cup- shaped or saucer-shaped vessels, and within them minute green bodies. If we examine a few of these minute bodies with the microscope we see that they are flattened, biconvex, and at two opposite points on the margin there is an indentation similar to that which appears at the growing end of the old marchantia thallus. These are the growing points of these little buds. When they free themselves from the cups they come to lie on one 154 MORPHOLOGY. side. It does not matter on what side they lie, for whichever side it is, that will develop into the lower side of the thallus, and forms rhizoids, while the upper surface will develop the stomates. Leafy-stemmed liverworts. 328. We should now examine more carefully than we have done formerly a few of the leafy-stemmed liverworts (called foliose liverworts). 329. Frullania (Fig. 60).—This plant grows on the bark of logs, as well as on the bark of standing trees. It lives in quite dry situations. If we examine the leaves we will see how it is able to do this. We note that there are two rows of lateral leaves, which are very close together, so close in fact that they overlap like the shingles on a roof. Fig. 187. Then, as the Section of thallus of marchantia. 4, through the middle portion ; : foo soe es 2 eae Gewese side (Goebel). lie very close to the bark of the tree, these overlapping leaves, which also hug close to the stem and bark, serve to retain moisture which trickles down the bark during rains. If we examine these leaves from the under side as shown in fig. 62, we see that the lower or basal part of each one is produced into a peculiar lobe which is more or less cup-shaped. This catches water and holds it during dry weather, and it also holds moisture which the plant absorbs during the night and in damp days. FOLIOSE LIVERWORTS. 155 There is so much moisture in these little pockets of the under side of the leaf that minute animals have found them good places to live in, and one frequently discovers them in this retreat. There is here also a third row of poorly developed leaves on the under side of the stem. 330. Porella.—Growing in similar situations is the plant known as porella. Sometimes there are a few plants in a group, and at other times large mats occur on the bark of a trunk. This plant, porella, also has closely overlapping leaves in rows on opposite sides of the stem, and the lower margin of each leaf is curved under somewhat as in frullania, though the pocket is not so well formed. The larger plants are female, that is they bear archego- nia, while the male plants, those which bear antheridia, are smaller and the an- theridia are borne on small lateral branches. The an- theridia are borne in the axils of the leaves. Others of the leafy-stemmed liverworts live in Pig,abs: ; ; Thallus of a thalloid liverwort (blasia) showing lobed damp situations. margin of the frond, intermediate between thalloid and Some of these, as fohose plant: Cephalozia, grow on damp rotten logs. Cephalozia is much more delicate, and the leaves are farther apart. It could not live in such dry situations where the frullania is sometimes found. If possible the two plants should be compared in order to see the adaptation in the structure and form to their environment. 331. Sporogonium of a foliose liverwort.—The sporogonium of the leafy-stemmed liverworts is well represented by that of several genera, We may take for this study the one illustrated 156 MORPHOLOG ¥. in fig. 192, but another will serve the purpose just as well. We note here that it consists of a rounded capsule borne aloft on a long stalk, the stalk being much longer proportionately than in -marchantia. At maturity the capsule splits down into four Fig. 190. Antheridium of a foliose liverwort (jun- germannia). Fig. 189. Fig. r9r. Foliose liverwort, male plant showing anthe- Foliose liverwort, female p.ant with ridia in axils of the leaves (a jungermannia). rhizoids. quadrants, the wall forming four valves, which spread apart from the unequal drying of the cells, so that the spores are set free, as shown in fig. 194. Some of the cells inside of the capsule de- velop elaters here also as well as spores, These are illustrated in fig. 196. 332, In this plant we see that the sporophyte remains attached FOLIOSE LIVERWORTS. 157 to the gametophyte, and thus is dependent on it for sustenance. This is true of all the plants of this group. The sporophyte never becomes capable of an independent existence, and yet we see that it is becoming larger and more highly differentiated than in the simple riccia. Fig. 193. Opening capsule showing escape of spores and elaters. iN). Fig. 194. Capsule pees down to the stalk. Vig. 192. Fruiting plant of a foliose liver- ig. 195. ie: abe wort Ganermannia), Leafy part Fig. 195 Fig. 196 is the gametophyte; stalk and cap- Four spores from Elaters, at left showing the two sule is the sporophyte (sporogonium mother cell held in spiral marks, at right a branched in the bryophytes). _ a group. elater. Figs. 193-196.—Sporogonium of liverwort (jungermannia) opening by splitting into four parts, showing details of elaters and spores. CHAPTER XXIV. MOSSES (MUSCI). 333. We are now ready to take up the more careful study of the moss plant. There are a great many kinds of mosses, and they differ greatly from each other in the finer details of struc- ture. Yet there are certain general resemblances which make it convenient to take for study almost any one of the common species in a neighborhood, which forms abundant fruit. Some, however, are more suited to a first study than others. (Polytri- chum and funaria are good mosses to study.) 334. Mnium.—We will select here the plant shown in fig. 197. This is known as a mnium (M. affine), and one or another of the species of mnium can be obtained without much difficulty, The mosses, as we have already learned, possess an avis (stem) and leaf-like expansions, so that they are leafy-stemmed plants also. Certain of the branches of the mnium stand upright, or nearly so, and the leaves are all of the same size at any given point on the stem, as seen in the figure. There are three rows of these leaves, and this is true of most of the mosses. 335. The mnium plants usually form quite extensive and pretty mats of green in shady moist woods or ravines. Here and there among the erect stems are prostrate ones, with two rows of promi- nent leaves so arranged that it reminds one of some of the leafy- stemmed liverworts. If we examine some of the leaves of the mnium we see that the greater part of the leaf consists of a single layer of green cells, just as is the case in the leafy-stemmed liverworts. But along the middle line is a thicker layer, so that it forms a distinct midrib. This is characteristic of the leaves 158 MOSSES. 159 of mosses, and is one way in which they are separated from the leafy-stemmed liverworts, the latter never having a midrib. 336. The fruiting moss plant.—In fig. 197 is a moss plant ‘‘in fruit,’’ as we say. Above the leafy stem a slender stalk bears the capsule, and in this capsule are borne the spores. The capsule then belongs to the sporophyte phase of the moss plant, and we should inquire whether the entire plant as we see it here is the sporophyte, or whether part of it is gametophyte. If a part of it is gametophyte and a part sporophyte, then where does the one end and the other begin? If we strip off the leaves at the end of the leafy stem, and make a longisection in the middle line, we should find that the stalk which bears the capsule is simply stuck into the end of the Portion of moss plant of Mnium affine, showing two sporogonia from one branch. Capsuleat left has just shed the cap or operculum ; capsule at right is shedding spores, and the teeth are bristling at the mouth. Next to the right is a young capsule with calyptra still attached; next are two spores enlarged. leafy stem, and is not organically connected with it. This is the dividing line, then, between the gametophyte and the sporo- phyte. We shall find that here the archegonium containing 160 MORPHOLOG Y. the egg is borne, which is a surer way of determining the limits of the two phases of the plant. 337. The male and female moss plants.—The two plants of mnium shown in figs. 198, I99 are quite different, as one can easily see, and yet they belong to the same species. One is a female plant, while the other is a male plant. The sexual organs then in mnium, as in many others of the mosses, are borne on separate plants. The archegonia are borne at the end of the stem, and are protected by somewhat narrower leaves which closely overlap and are wrapped together. They are similar to the archegonia of the liverworts. Fig. 108. Vig. 199. Female plant (gametophyte) of a moss Male plant (gametophyte) of a moss (mnium), showing rhizoids below, and the (mnium) showing rhizoids below and the tuft of leaves above which protect the arche- antheridia at the center above surrounded by gonia. the rosette of leaves. The male plants of mnium are easily selected, since the leaves at the end of the stem form a broad rosette with the antheridia, and some sterile threads packed closely together in the center. The ends of the mass of antheridia can be seen with the naked eye, as shown in fig. 199. When the antheridia MOSSES. 161 are ripe, if we make a section through a cluster, or if we merely tease out some from the end with a needle in a drop of water on the slide, then prepare for examination with the microscope, we can see the form of the antheridia. They are somewhat clavate or elliptical in outline, as seen in fig. 201. Be- tween them there stand short threads composed of several cells containing chlorophyll grains. These are sterile threads (paraphyses). 338. Sporogonium.—lIn fig. 197 we see illustrated a sporogonium of mnium, which is of course developed from the fertilized egg cell of the archegonium. There is a nearly cylindrical capsule, bent downward, and supported ona long TT Tit se2 i cr \ Dr 3 H\ q . Ke fl | oft ova Hl ease A 1H | eh Yon 4 | AS a ‘th rete ‘\ C] ‘a PA Kar H ry || ERO H A RS Be 74 HEE A Hawt eo | AX [ A eS RR | ase A ee Span EM Oe ot Alt ee MAL Bx] ty Wy 4 0 .Y) RE Hy IN wi ABO KEN Yon o h/? wes KA EES i GAH ENA aN ie Breet = its Fig. 201. Fig. 200. Antheridium of mnium Section through end of stem of female plant of mnium, show- with jointed paraphysis ing archegonia at the center. One archegonium shows the egg. at the left ; _ Spermato- On the sides are sections of the protecting leaves. zoids at the right. slender stalk. Upon the capsule is a peculiar cap,* shaped like a ladle or spatula. This is the remnant of the old archegonium, which, for a time sur- rounded and protected the young embryo of the sporogonium, just as takes place in the liverworts. In most of the mosses this old remnant of the arche- gonium is borne aloft on the capsule as a cap, while in the liverworts it is thrown to one side as the sporogonium elongates. 339. Structure of the moss capsule.—At the free end on the moss capsule * Called the calyptra. 162 MORPHOLOG Y. as shown in the case of mnium in Fig. 197, after the remnant of the arche- gonium falls away, there is seen a conical lid which fits closely over the end. When the capsule is ripe this lid easily falls away, and can be brushed off so that it is necessary to handle the plants with care if it is desired to preserve this for study. 340. When the lid is brushed away as the capsule dries more we see that the end of the capsule covered by the lid appears ‘‘frazzled.”’ If we examine this end with the micro- scope we see that the tissue of the capsule here is torn with great regularity, so that there are two rows of narrow, sharp teeth which project outward in a ring around the opening. If we blow our ‘‘breath”’ upon these teeth they will be seen to move, and as the moisture disappears and reappears in the teeth, they close and open the mouth of the capsule, so sensi- tive are they to the changes in the humidity of the air. In this way all of the spores are prevented to some extent from escaping from the capsule at one time. 841. Note. If we make a sec- tion longitudinal of the capsule of mnium, or some other moss, we find that the tissue which develops the spores is much more restricted than in the capsule of the liver- worts which we have studied. The spore-bearing tissue is confined to a single layer which extends around the capsule some distance from the Fig. 202. outside of the wall, so that a central Two different stages of young sporogonium of cylinder is left of sterile tissue. a moss, still within the archegonium and wedg- ve . ‘ ing their way into the tissue of the end of the stem. a is the columella, and is pres 4, neck of archegonium ; 7, young sporogonium. ent in nearly all the mosses. Each ane we tae RUIES Doren? of the cells of the fertile layer divides into four spores. 342. Development of the sporogonium.—The egg cell after fertilization divides by a wall crosswise to the axis of the archegonium. Each of these cells continues to divide for a time, so that a cylinder pointed at both ends is formed. The lower end of this cylinder of tissue wedges its way down through the base of the archegonium into the tissue of the end of the moss stem as shown in fig. 202. ‘This forms the fvot through which the nutrient MOSSES. 163 materials are passed from the gametophyte to the sporogonium. The upper part continues to grow, and finally the upper end differentiates into the mature capsule. 843. Protonema of the moss.—When the spores of a moss germinate they form a thread-like body, with chlorophyll. This thread becomes branched, and sometimes quite extended tangles of these threads are formed. This is called the protonema, that is fst ¢hread. The older threads become finally brown, while the later ones are green. From this protonema at certain points buds appear which divide by close oblique walls. From these buds the leafy stem of the moss plant grows. Threads similar to these protonemal threads now grow out from the leafy stem, to form the rhizoids. These supply the moss plant with nutriment, and now the protonema usually dies, though in some few species it persists for long periods. MORPHOLOGY. 164 Cumtuosayore (‘eur . jo yuruurar si i : -[evads eieaae umuogo1ods uo quer ae ap a pue Sone ee ae 942 } *sarodg|"*:: sdoyaaap| ‘ aye *qy90} § TT “eTTour PROF eaydayed) OTE 40 es oe -qodo010ds uada)-auojoid dates ue uo WAHD 5 1 taaiiiaties a -nyoo okay: eas (uma yuvyd ayewayjpua we ‘SPlOZ! 5 isoavay ‘sixeauo “(emueusadun(| YL TOg Bu sre ate 09 He atnsdeo t i eni|-o8or0ds sdo|MO ‘399 YIM Yora|-oyeutiads UIA g Siatio} 0} er its) saavay jo ‘“iawNa 4 ee Ss ae ses st einaeos pal-jaaaq) *33a ‘eyuoSayory |erpraeyyuy | oyg a yamosd Aq smo i ‘sixe AEs aUe. “WAIN -ARy peouipurpc: -yyeys jouredapuais 9 Z1] Id. *squerd yuosayip uw ‘Suryouesq A -tedde YM jurg “SASSOJY TTESMpayAD [-ATEIS F THAIS |pezt yey T IP uO it q Ad Tt I yuryd “sjurrd aeway pue *siaqepa pue $13} SIEM 90! 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Aeme 3ursp Aq |‘pauaney snqyey, -NVHOAVJT “yea “Sploz (coma at 33a yyml-oyeureds yt “sued sapyo *sad0dg| +++ ++++-- sdopaaap “s][20. -o8010ds sdo ‘eyuosayory |‘erprrayiay jo Aeme SutAp *ae[no419 Apieau 10 (unt10dsayore)|takey-auo yo ‘ummu|-[349(q) “330 “snTTeIY JO Yo prem |pue Buroursq ‘paysoy ‘ayr]-uoqqu 2 sseur yenuad |-oSo10ds jo [eAy pazyyieg —|-dn ‘Surpunorms Aq pasiaumy = |Aq saumauog |‘pauayey suey ‘VIDIIY “HLAHd “NOIL 3 ‘ALAHdOL | LUV ATILYaY| ‘LUV AIYALS -oN0dS 4O “SNVDYQ TVAXES -VOITdGILINYY ONES aia ONINNIOR HAILVLaDa A SAMY LEO: ONINNIOAG JUSUIYSLIMNOU IOF 1 uo JUapusdap pue Sie a 0} payseny) ALAHdMOXOdS SASSO (-aoua3sixe yuapuadaepur uv spray "ued ayy yo pred quaummorg) “TL AHAOLANVD CQNV SLUOMUAATT AHL NI ALAHdOUWOdS ANV ALAHAOLANVYS AO NOILLVIAM ONLMOHS WIAVL ‘Pts CHIAPTER XXV. | FERNS. 345. In taking up the study of the ferns we tind plants which are very beautiful objects of nature and thus have alwaysattracted the interest of those who love the beauties of nature. But they are also very interesting to the student, because of certain re- markable peculiarities of the structure of the fruit bodies, and especially because of the intermediate position which they occupy within the plant kingdom, representing in the two phases of their development the primitive type of plant life on the one hand, and on the other the modern type. We will begin our study of the ferns by taking that form which is the more promi- nent, the fern plant itself. 346. The Christmas fern.—One of the ferns which is very common in the Northern States, and occurs in rocky banks and woods, is the well-known Christmas fern (Aspidium acrostichoides) shown in fig. 203. The leaves are the most prominent part of the plant, as is the case with most if not all our native ferns. The stem is very short and for the most part under the surface of the ground, while the leaves arise very close together, and thus form a rosette as they rise and gracefully bend outward. The leaf is elongate and reminds one somewhat of a plume with the pinne extending in two rows on opposite sides of the midrib. These pinne alternate with one another, and at the base of each pinna is a little spur which projects upward from the upper edge. Such a leaf is said to be pinnate. While all the leaves have the same general outline, we notice that certain ones, especially those toward the center of the rosette, are much narrower from the 165 166 MORPHOLOGY. middle portion toward the end. This is because of the shorter pinne here. 347. Fruit “dots” (sorus, indusium).—If we examine the under side of such short pinnz of the Christmas fern we see that there are two rows of small circular dots, one row on either side of the pinna. These are called the ‘é fruit dots,’’ or sori (a single one is asorus). If we examine it with a low power of the mi- croscope, or with a pocket lens, we see that there is a circular disk which covers more or % ff less com- pletelyvery minute objects, usual- ly the ends of the latter projecting just be- yond the edge if they are mature. This circular disk is what is called the indu- sium, and it is a special outgrowth of the epidermis of the leaf here for the protection of the spore- cases. These minute ob- Christmas fern ican acrostichoides). jects underneath are: the fruit bodies, which in the case of the ferns and their allies are called sporangia. This indusium in the case of the Christmas fern, and also in some others, is attached to the leaf by means of a short slender stalk FERNS. 167 which is fastened to the middle of the under side of this shield, as seen in cross section in fig. 209. 348. Sporangia. —If we section through the leaf at one of the fruit dots, or if we tease off some of the sporangia so that the Ff iy stalks are still attached, and y 4 iy \ qi ' ‘ ‘ i I; examine them with the mi- \ Mbit. | by croscope, we can see the hi form and structure of these peculiar bodies. Different views of a sporangium are shown in fig. 210. The slender portion is the stalk, and the larger part is the spore-case proper. We should examine the structure of this spore-case quite care- fully, since it will help us to understand better than we otherwise could the remark- able operations which it performs in scattering the spores. 349. Structure of a spo- rangium. —If we examine one of the sporangia in side y view as shown in fig. 210, Fig. 204. we note a prominent row of Rhizome with bases of leaves, and roots of the ce]]s which extend around Christmas fern. the margin of the dorsal edge from near the attachment of the stalk to the upper front angle. The cells are prominent because of the thick inner walls, and the thick radial walls which are perpendicular to the inner walls. The walls on the back of this row and on its sides are very thin and membranous. We should make this out carefully, for the structure of these cells is especially adapt- ed to a special function which they perform, This row of cells 168 MORPHOLOG Y. is termed the annulus, which means a little ring. While this is not a complete ring, in some other ferns the ring is nearly complete. 350. In the front of the sporangium is another peculiar group Fig. 205. Rhizome of sensitive fern (Onoclea sensibilis). of cells. Two of the longer ones resemble the lips of some crea- ture, and since the sporangium opens between them they are sometimes termed the lip cells. These lip cells are connected with the upper end of the annulus on one side and with the upper end of the stalk on the other side by thin-walled cells, which may be termed connective cells, since they hold each lip cell to its part of the opening sporangium. ‘The cells on the side of the sporangium are also thin-walled. If we now examine a sporangium from the back, or dorsal Fig. 206. Under side of pinnaof Aspidium edge as we say, it will appear as in the spinulosum showing fruit dots (sori). left-hand figure. Here we can see how very prominent the annulus is. It projects beyond the surface of the other cells of the sporangium, The spores are contained inside this case, FERNS. 169 351. Opening of the sporangium and dispersion of the spores.—If we take some fresh fruiting leaves of the Christmas fern, or of any one of many of the species of the true ferns just at the ripening of the spores, and place a portion of it ona piece of white paper in a dry room, in a very short time we shall see that the paper is being dusted with minute brown objects which fly out from the leaf. Now if we take a portion of the same leaf and place it under the low power of the microscope, so that the full rounded sporangia can be seen, in a short time we note that the sporangium opens, the upper half curls backward as Fig. 207. Four pinnz of adiantum, showing recurved margins which cover the sporangia. shown in fig. 211, and soon it snaps quickly, to near its former position, and the spores are at the same time thrown for a consid- erable distance. This movement can sometimes be seen with the aid of a good hand lens. 352. How does this opening and snapping of the sporan- gium take place ?—We are now more curious than ever to see just how this opening and snapping of thesporangium takes place. We should now mount some of the fresh sporangia in water and cover with a cover glass for microscopic examination. A drop of glycerine should be placed at one side of the cover glass on the slip so that the edge of the glycerine will come in touch with the water. Now as one looks through the microscope to watch the 170 MORPHOLOGY. sporangia, the water should be drawn from under the cover glass with the aid of some bibulous paper, like filter paper, placed at the edge of the cover glass on the opposite side from the glycerine. As the glycer- ine takes the place of the water around the sporangia it draws the water out of the cells of the annulus, just as it took the water out of the cells of the spirogyra as we learned some time ago. As the water is drawn out of these cells there is produced a pressure from without, the atmospheric pressure upon the glycerine. This causes the walls of these cells of the annulus to bend _ in- ward, because, as we have Fig. 208. already learned, the glycer- ssceing” ARC? ate? ff sponbgtnn aaice ine does not pass through upeelular capiate hate, the walls nearly so fast as the water comes out. 358. Now the structure of the cells of this annulus, as we have seen, is such that the inner walls and the perpendicular Fig. 209. Section through sorus and shield-shaped indusium of aspidium, walls are stout, and consequently they do not bend or collapse when this pressure is brought to bear on the outside of the cells, FERNS. 171 The thin membranous walls on the back (dorsal walls) and on the sides of the annulus, however, yield readily to the pressure and bend inward. This, as we can readily see, pulls on the ends of each of the perpendicular walls drawing them closer together. This shortens the outer surface of the annulus and causes it to first assume a nearly straight position, then curve backward until it quite or nearly becomes doubled on itself. The sporangium hy Fig. 210. Rear, side, and front views of fern sporangium. a, e, annulus; a, lip cells. opens between the lip cells on the front and the lateral walls of the sporangium are torn directly across. The greater mass of spores are thus held in the upper end of the open sporangium, and when the annulus has nearly doubled on itself it suddenly snaps back again in position. While treating with the glycerine we can see all this movement take place. Each cell of the annulus acts independently, but often they all act in concert. When they do not all act in concert, some of them snap sooner than others, and this causes the annulus to snap in segments. 354. The movements of the sporangium can take place in old and dried material.—If we have no fresh material to study 172 MORPHOLOGY. the sporangium with, we can use dried material, for the move- ments of the sporangia can be well seen in dried material, pro- vided it was collected at about the time the sporangia are mature, that is at maturity, or soon afterward. We take some of the dry sporangia (or we may wash the glycerine off those which we have just studied) and mount them in water, and quickly examine vs Ls Fig. 20. Dispersion of spores from sporangium of Aspidium acrostichoides, showing different stages in the opening and snapping ot the annulus. them with a microscope. We notice that in each cell of the annulus there is a small sphere of some gas. The water which bathes the walls of the annulus is absorbed by some substance inside these cells. This we can see because of the fact that this sphere of gas becomes smaller and smaller until it is only a mere FERNS. 173 dot, when it disappears ina twinkling. The water has been taken in under such pressure that it has absorbed all the gas, and the farther pressure in most cases closes the partly opened sporangium more completely. 355. Now we should add glycerine again and draw out the water, watching the sporangia at the same time. We see that the sporangia which have opened and snapped once will do it again. And so they may be made to go through this operation several times in succession. We should now note carefully the annulus, that is after the sporangia have opened by the use of glycerine. So soon as they have snapped in the glycerine we can see those minute spheres of gas again, and since there was no air on the outside of the sporangia, but only glycerine, this gas must, it is reasoned, have been given up by the water before it was all drawn out of the cells. 356. The common polypody.—We may now take up a few other ferns for study. Another common fern is the polypody, one or more species of which have avery wide distribution. The stem of this fern is also not usually seen, but is covered with the leaves, except in the case of those species which grow on the surface of rocks. The stem is slender and prostrate, and is covered with numerous brown scales, The leaves are pinnate in this fern also, but we find no difference between the fertile and sterile leaves (except in some rare cases). The fruit-dots occupy much the same positions on the under side of the leaf that they do in the Christmas fern, but we cannot find any indusium, In the place of an indusium are club-shaped hairs as shown in fig. 208. The en- larged ends of these clubs reaching beyond the sporangia give some protection to them when they are young. 357. Other ferns.—We might examine a series of ferns to see how different they are in respect to the position which the fruit dots occupy on the leaf. The common brake, which sometimes covers extensive areas and becomes a trouble- some weed, hasa stout and smooth underground stem (rhizome) which is often 12 to 20 cm beneath the surface of the soil. There is a long leaf stalk, which bears the lamina, the latter being several times pinnate. The margins of the fertile pinnee are inrolled, and the sporangia are found protected underneath in this long sorus along the margin of the pinna. The beautiful maidenhair fern and its relatives have obovate pinnz, and the sori are situated in the same posi- tions as in the brake. In other ferns, as the walking fern, the sori are borne along by the side of the veins of the leaf. 358. Opening of the leaves of ferns.—The leaves of ferns open in a peculiar manner. ‘The tip of the leaf is the last portion developed, and the growing 174 MORPHOLOGY. leaf appears as if it was rolled up as in fig. 204 of the Christmas fern. As the leaf elongates this portion unrolls, 359. Longevity of ferns.—Most ferns live from year to year, by growth adding to the advance of the stem, while by decay of the older parts the stem shortens up behind. The leaves are short-lived, usually dying down each year, and a new set arising from the growing end of the stem. Often one can see just back or below the new leaves the old dead ones of the past season, and farther back the remains of the petioles of still older leaves. 360. Budding of ferns. — A few ferns produce what are called bulbils or bulblets on the leaves. One of these, which is found throughout the greater part of the eastern United States, is the bladder fern (Cystop- teris bulbifera), which grows in shady rocky places. The long graceful delicate leaves form in the axils of the pinne, especially near the end of the leaf, small oval bulbs as shown in fig. 212, If we examine one of these bladder-like bulbs we see that the bulk of it is made up of short thick fleshy leaves, smaller ones ap- pearing between the outer ones at the smaller end of the bulb. This bulb contains a stem, young root, and several pairs of these fleshy leaves. They easily fall to the ground or rocks, where, with the abundant moisture usually present in localities where the fern is found, the bulb Fig. 212. Cystopteris bulbifera, young plant growing STOWS until the roots attach the plant ae ss right is young bulb in axil of to the soil or in the crevices of the rocks. A young plant growing from one of these bulbils is shown in fig. 212. 361. Greenhouse ferns.—Some of the ferns grown in conservatories have similar bulblets. Fig. 213 represents one of these which is found abundantly on the leaves of Asplenium bulbiferum. These bulbils have leaves which are very similar to the ordinary leaf except that they are smaller. The bulbs are also much more firmly attached to the leaf, so that they do not readily fall away. 362. Plant conservatories usually furnish a number of very interesting ferns, and one should attempt to make the acquaintance of some of them, for FERNS. 175 here one has an opportunity during the winter season not only to observe these interesting plants, but also to obtain material for study. In the tree ferns which often are seen growing in such places we see examples of the massive trunks and leaves of some of the tropical species. 363. The fern plant is a sporophyte.—We have now studied the fern plant, as we call it, and we have found it to represent the spore-bearing phase of the plant, that is the sporophyle (cor- responding to the sporogonium of the liverworts and mosses). 364. Is there a ga- metophyte phase in ferns ?—But in the spor- ophyte of the fern, which we should not forget is the fern plant, we have a striking advance upon the sporophyte of the liverworts and mosses. In the latter plants the sporophyte remained attached to the gameto- phyte, and derived its nourishment from it. In the ferns, as we see, the sporophyte has a root of its own, and is Heck attached to the soil. Bulbil growing from leaf of asplenium (4, bulbiferum). Through the aid of root : hairs of its own it takes up mineral solutions. It possesses also a true stem, and true leaves in which carbon conversion takes place. It is able to live independently, then. Does a gametophyte phase exist among the ferns? Or has it been lost? If it does exist, what is it like, and where does it grow? From what we have already learned we should expect to find the gametophyte begin with the germination of the spores which are developed on the sporophyte, that is on the fern plant itself. We should investigate this and see. CHAPTER XXVI. FERNS CONTINUED. Gametophyte of ferns. 365. Sexual stage of ferns.—We now wish to see what the sexual stage of the ferns is like. Judging from what we have found to take place in the liverworts and mosses we should infer Fig. arg. Prothallium of fern, under side, showing rhizoids, antheridia scattered among and near them, and the archegonia near the sinus. that the form of the plant which bears the sexual organs is de- veloped from the spores. This is true, and if we should examine old decaying logs, or decaying wood in damp places in the near 176 FERNS. 177 vicinity of ferns, we should probably find tiny, green, thin, heart- shaped growths, lying close to the substratum. These are also found quite frequently on the soil of pots in plant conservatories where ferns are grown. Gardeners also in conservatories usually sow fern spores to raise new fern plants, and usually one can find these heart-shaped growths on the surface of the soil where they have sown the spores. We may call the gardener-to our aid in finding them in conservatories, or even in growing them for us if we cannot find them outside. In some cases they may be grown in an ordinary room Fig. 215. 5 Spore of Pteris serru- by keeping the surfaces where they are _ lata showing the three- . 5 = ; rayed elevation along growing moist, and the air also moist, by _ the side of which the : spore wall cracks during placing a glass bell jar over them. germination. 366. In fig. 214 is shown one of these growths enlarged. Upon the under side we see numerous thread-like outgrowths, the rhizoids, which attach the plant to the substratum, and which act as organs for the absorption of nourishment. ‘The sexual organs are borne on the under side also, and we will study them later. This heart-shaped, Figs Sat: ipo flattened, thin, Spore of Aspidium Spore crushed to remove exospore and green plant 1S acrostichoides with show endospore. 3 winged exospore. the prothallium of ferns, and we should now give it more careful study, be- ginning with the germination of the spores. 367. Spores.—We can easily obtain material for the study of the spores of ferns. The spores vary in shape to some extent. Many of them are shaped like a three-sided pyramid. One of these is shown in fig. 215. The outer wall is roughened, and on one end are three elevated ridges which radiate from a given 178 MORPHOLOGY. point. A spore of the Christmas fern is shown in fig. 216. The outer wall here is more or less winged. At fig. 217 is a spore of the same species from which the outer wall has been crushed, showing that there is an inner wall also. If possible we should study the germi- nation of the spores of some fern. 368. Germination of the spores. —After the spores have been sown for about one week to ten days we should Fig. 218. taf e ter f Scat Spores of asplenium ; exospore re. MOunt a few in water for examination Moved fromthevone at theriehts with the microscope in order to study the early stages. If germination has begun, we find that here and there are short slender green threads, in many cases attached to brownish bits, the old walls of the — spores. Often one will sow the 3} sporangia along with the spores, and in such cases there may be found a number of spores. still within the old sporan- gium wall that are ger- minating, when they will appear as in fig. 219. 369. Protonema.— These short green threads are sited protonemal threads, or profonema, which means a first thread, and it here signifies that this short thread only pre- cedes a larger growth of the same object. In figs. 219, 220 are shown several stages of _ germination of different spores. Soon after Fig. 219. Germinating spores of the short germ tube emerges from the is aquilina still in t ‘ wae se RE aa sulin the Crack in the spore wall, it divides by the FERNS. 179 formation of a cross wall, and as it increases in length other cross walls are formed. But very early in its growth we see that a slender outgrowth takes place from the cell nearest the old spore wall. ‘This slender thread is colorless, and is not divided into cells. It is the first rhizoid, and serves both as an organ of attachment for the thread, and for taking up nutriment. 370. Prothallium.—Very soon, if the sowing has not been so crowded as to prevent the young plants from obtaining nutriment sufficient, we will see that the end of this protonema is broadening, as shown in fig, 220. This is done by the formation of the cell walls in different directions. It now continues to grow in this way, the end becoming broader and broader, and new rhizoids are formed from the under surface of the cells. The growing point remains at the mid- dle of the advancing margin, and the cells which are cut off from either side, as they become old, ; widen out. In this way: the Young auaien ot a fern (nipho- ‘‘wings,’? or margins of the bel). little, green, flattened body, are in advance of the growing point, and the object is more or less heart-shaped, as shown in fig. 214. Thus we see how the prothallium of ferns is formed. : 371. Sexual organs of ferns.—If we take one of the prothal- lia of ferns which have grown from the sowings of fern spores, or one of those which may be often found growing on the soil 180 MORPHOLOGY. of pots in conservatories, mount it in water on a slip, with the under side uppermost, we can then examine it for the Fig. 221. Male prothallium of a fern (niphobolus), in form of an alga or protonema. Spermato- zoids escaping from antheridia. sexual organs, for these are borne in most cases on the under side. 372. Antheridia.—If we search among the rhizoids we see small rounded elevations as shown in fig. 214 or 222 scat- Fig. 222. Male prothallium of fern (niphobolus), showing opened and unopened antheridia ; section of unopened antheridium , spermatozoids escaping ; spermatozoids which did not escape from the antheridium, FERNS. 181 tered over this portion of the prothallium. These are the an- theridia. If the pro- thallia have not been watered for a day or so, we may have an opportunity of see- ing the spermato- zoids coming out of the antheridium, for when the prothallia Section of antheridia 7 ee cells, and spermato- are freshly placed jn zoids in the one at the right. water the cells of the antheridium ab- sorb water. This presses on the con- tents of the antheridium and bursts the cap cell if the antheridium is ripe, and all thé spermatozoids are shot out. We can see here that each one is ‘Spee shaped like a screw, with the coils at Different views of spermatozoids; first close. But as the spermatozoid 42, 43, in a quiet condition; 44, in j = ‘ motion (Adiantum concinnum). begins to move this coil opens some- what and by the vibration of the long cilia which are on the smaller end it whirls away. In such preparations one may often see them spinning around for a long while, and it is only when they gradually come to rest that one can make out their form. 373. Archegonia.—If we now examine closely on the thicker part of the under surface of the prothallium, just back of the = : “‘sinus,’’? we may see longer oantee Ore eee fet te ieee al cae cell, and in the canal of the neck are two stout projections from the surface nuclei of the canal cell. of the prothallium. These are shown in fig. 214. They are 182 MORPHOLOGY. the archegonia. One of them in longisection is shown in fig. 225. It is flask-shaped, and the broader portion is sunk in the Fig. 226. Mature and open archegonium of fern (Adiantum cuneatum) with spermatozoids making their way down through the slime to the egg. tissue of the prothallium. The egg isin the larger part. The spermatozoids when they are swimming around over the under surface of the pro- thallium come near the neck, and here they are caught in the viscid substance which has oozed out of the canal of the arche- gonium. From here they slowly swim down the canal, and finally one sinks into Fig. 227. the egg, fuses with the nucleus of the latter, fertilization in a fem and the egg is then fertilized. It is now (Marattia). sf, spermato- id fusing with the nu- : 20d Cee es ‘after ready to grow and develop into the fern cael plant. This brings us back to the sporo- phyte, which begins with the fertilized egg. Sporophyte. 874. Embryo.—The egg first divides into two cells as shown in fig. 228, then into four. Now from each one of these quandrants of the embryo a definite part of the plant develops, from one the first leaf, from one the stem, from one the root, and from the other the organ which is called the foot, and which FERNS. 183 attaches the embryo to the prothallium, and transports nourishment for the embryo until it can become attached to the soil and lead an independent ex- istence. During this time the wall of the archegonium grows somewhat to accommodate the increase in size of the embryo, as shown in figs. 229, 230. But soon the wall of the archegonium is ruptured and the embryo emerges, the root attaches itself to the soil, and soon the prothallium dies. The embryo is first on the under side of the prothallium, and the first leaf Fig. 228. Two-celled embryo of Pteris serrulata. Remnant of archegonium neck below. and the stem curves upward between the lobes of the heart-shaped body, and then grows upright as shown in fig. 231. Usually only one embryo is formed on a single prothallium, but in one case I found a prothallium with two well- formed embryos, which are figured in 232. 375. Comparison of ferns with liverworts and mosses.—In the ferns then we have reached a remarkable condition of things as compared with that which we found in the mosses and liverworts. In the mosses and liverworts 184 MORPHOLOGY. the sexual phase of the plant (gametophyte) was the prominent one, and consisted of either a thallus or a leafy axis, but in either case it bore the sexual organs and led an independent existence; that is it was capable of ob- taining its nourishment from the soil or water by means of organs of absorp- tion belonging to itself, and it also performed the office of carbon conversion. 376. The spore-bearing phase (sporophyte) of the liverworts and mosses, on the other hand, is quite small as compared with the sexual stage, and it is Fig. 229. Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium. 5S, stem; L, first leaf or cotyledon; 7, root; /, foot. completely dependent on the sexual stage for its nourishment, remaining at- tached permanently throughout all its development, by means of the organ called a foot, and it dies after the spores are mature. 877. Now in the ferns we see several striking differences. In the first place, as we have already observed, the spore-bearing phase (sporophyte) of FERNS. 185 the plant is the prominent one, and that which characterizes the plant. It also leads an independent existence, and, with the exception of a few cases, does not die after the development of the spores, but lives from year to year and develops successive crops of spores. There is a distinct advance here in the size, complexity, and permanency of this phase of the plant. 378. On the other hand the sexual phase of the ferns (gametophyte), while it still is capable of leading an independent existence, is short-lived (with very few exceptions). It is also much smaller than most of the liverworts and Fig. 230. Embryo of fern (Adiantum concinnum) still surrounded by the archegonium, which has grown in size, forming the ‘‘calyptra.”” Z, leaf; S, stem; A, root; /, foot. mosses, especially as compared with the size of the spore-bearing phase. The gametophyte phase or stage of the plants, then, is decreasing in size and durance as the sporophyte stage is increasing. We shall be interested to see if this holds good of the fern allies, that is of the plants which belong to the same group as the ferns. And as we come later to take up the study of the higher plants we must bear in mind to carry on this comparison, and see if this progression on the one hand of the sporophyte continues, and if the retrogression of the gametophyte continues also, 186 MORPHOLOG Y. Fig. 232. Two embryos from one prothallium of attached to prothallium. Adiantum cuneatum. Fig. 231. Young plant of Pteris serrulata still CHAPTER XXVIL. HORSETAILS. 879. Among the relatives of the ferns are the horsetails, so called because of the supposed resem- blance of the branched stems of some of the species to a horse’s tail, as one might infer from the plant shown in fig. 237. They do not bear the least re- semblance to the ferns which we have been study- ing. But then relationship in plants does not depend on mere resemblance of outward form, or of the promi- nent part of the plant. 380. The field equisetum. Fertile shoots.—Fig. 233 represents the common horsetail (Equisetum ar- vense). It grows in moist sandy or gravelly places, and the fruiting portion of the plant (for this species is dimorphic), that is the portion which bears the spores, appears above the ground early in the spring. It is one of the first things to peep out of the recently frozen ground. ‘This fertile shoot of the plant does not form its growth this early in the spring. Its development takes place under the ground in the autumn, so that with the advent of spring it pushes up without delay. This shoot is from 10 to 20 cm high, and at quite regular intervals there are slight enlargements, the nodes of the stem. The cylindrical portions between the nodes are the _ internodes. If we examine the region of the inter- Sore € fertile plant of nodes carefully we note that there are thin mem- ¢guisetum ar- branous scales, more or less triangular in outline, and Y9nsqshowng leaves and the connected at their bases into a ring around the stem. fruiting spike. 187 188 MORPHOLOGY. Curious as it may seem, these are the leaves of the horsetail. The stem, if we examine it farther, will be seen to possess numer- ous ridges which extend lengthwise and which alternate with furrows. Farther, the ridges of one node alternate with those of the internode both above and below. Likewise the leaves of one node alternate with those of the nodes both above and below. 381. Sporangia.—The end of this fertile shoot we see pos- sesses a cylindrical to conic enlargement. This is the /eri/e spike, and we note that its surface is marked off into regular areas if the spores have not yet been disseminated. If we dissect off a few of these por- tions of the fertile spike, and examine one of them with a low magnifying power, it will appear like the : fig. 234. We see here that the angular area is a Fig. 234. disk-shaped body, with a stalk attached to its inner Pettate opot surface, and with several long sacs projecting from phyll of equisetum jside view) show- its inner face parallel with the stalk and surrounding ing sporangia on wader Se; the same. These elongated sacs are the sporangia, and the disk which bears them, together with the stalk which attaches it to the stem axis, is the sporophy//, and thus belongs to the leaf series. These sporophylls are borne in close whorls on the axis. 382. Spores.—When the spores are ripe the tissue of the sporangium becomes dry, and it cracks open and the spores fall out. Ifwe look at fig. 235 we see that the spore is covered with a very singular coil which lies close to the wall. When the spore dries this uncoils and thus rolls the spore about. Merely breathing upon these spores is sufficient to make them perform very curious evolutions by the twisting of these four coils which are attached to one place of the wall. ‘They are formed by the splitting up of an outer wall of the spore. 383. Sterile shoot of the common horsetail.—When the spores are ripe they are soon scattered, and then the fertile shoot dies down. Soon afterward, or even while some of the fertile shoots are still in good condition, sterile shoots of the HORSETAILS. 189 plant begin to appear above the ground. One of these is shown in fig. 237. This has a much more slender stem and is pro- Spore of equisetum Spore of equisetum with elaters un- with elaters coiled up. coiled. vided with numerous branches. If we ex- amine the stem of this shoot, and of the branches, we see that the same kind of leaves are present and that the markings on the stem are similar. Since the leaves of the horsetail are membranous and not green, the stem is green in color, and this per- forms the function of carbon conversion. These green shoots live for a great part of the season, building up material which is carried down into the underground stems, where it goes to supply the forming fertile shoots in the fall. On digging up some of these plants we see that the underground stems are often of great extent, and that both fertile and sterile shoots are attached to one and the same. 384. The scouring rush, or shave grass. —Another common species of horsetail in the Northern States grows on wet banks, or in sandy soil which contains moisture along railroad embankments. It is the scouring rush (E. hyemale), so called because it was once used for polishing purposes. This plant like Fig. 237. ; ; terile plant of horsetai i. all the species of the horsetails has a orselail (Equs 190 MORPHOLOGY. underground stems. But unlike the common horsetail, there is but one kind of aerial shoot, which is green in color and fertile. The shoots range as high as one meter or more, and are quite stout. The new shoots which come up for the year are un- branched, and bear the fertile spike at the apex. When the spores are ripe the apex of the shoot dies, and the next season small branches may form from a number of the nodes. 385. Gametophyte of equisetum.—The spores of equisetum have chloro- phyll when they are mature, and they are capable of germinating as soon as mature. The spores are all of the same kind as regards size, just as we found in the case of the ferns. But they develop prothallia of different sizes, according to the amount of nutriment which they obtain. Those which obtain but little nutriment are smaller and develop only antheridia, while those which obtain more nutriment become larger, more or less branched, and develop archegonia. This character of an independent pro- thallium (gametophyte) with the characteristic sexual organs, and the also independent sporophyte, with spores, shows the relationship of the horsetails with the ferns. We thus see that these characters of the reproductive organs, and the phases and fruiting of the plant, are more essential in deter- mining relationships of plants than the mere outward appearances. CHAPTER XXVIII. CLUB MOSSES. 386. What are called the ‘‘ club mosses’’ make up another group of interesting plants which rank as allies of the ferns. They are not of course true mosses, but the general habit of some of the smaller species, and especially the form and size of the leaves, suggest a resem- blance to the larger of the moss plants. 387. The clavate lycopodium.—Here is one of the club mosses (fig. 238) which has a wide distribution and which is well entitled to hold the name of club because of the form of the up- right club-shaped branches. As will be seen from the illustration, it has a prostrate stem. This stem runs for considerable distances on the surface of the ground, often partly buried in the leaves, and sometimes even buried beneath the soil. ‘The leaves are quite small, are flat- tened-awl-shaped, and stand thickly over the stem, arranged in a spiral manner, which is the usual arrangement of the leaves of the club mosses. Here and there are upright branches which are forked several times. The end of one or more of these branches becomes pro- , duced into a slender upright stem which is igre pies nearly leafless, the leaves being reduced to im branch bearite twa = sporophyll with open mere scales. The end of this leafless branch Coregims staele then terminates in one or several cylindrical sPote ner it heads which form the club. gl 192 MORPHOLOGY. 388. Fruiting spike of Lycopodium clavatum.—This club is the fruiting spike or head (sometimes termed a s/roddlus). Here the leaves are larger again and broader, but still not so large as the leaves on the creeping shoots, and they are paler. If we bend down some of the leaves, or tear off a few, we see that in the axil of the leaf, where it joins the stem, there is a somewhat rounded, kidney-shaped body. This is the spore-case or spo- rangium, as we can see by an examination of its contents. There is but a single spore-case for each of the fertile leaves (sporophyll). When it is mature, it opens by a crosswise slit as seen in fig. 238. When we consider the number of spore-cases in one of these club- shaped fruit bodies we see that the number of spores developed ina large plant is immense. In mass the spores make a very fine, soft powder, which is used for some kinds of pyrotechnic material, and for various toilet purposes. 389. Lycopodium lucidulum.—Another com- A mon species is figured at 239. This is Lycopo- - iN dium lucidulum. The habit of the plant is quite Sa \— different. It grows in damp ravines, woods, and SS moors. The older parts of the stem are prostrate, A ~~ while the branches are more or less ascending. It branches in a forked manner. The leaves are larger than in the former species, and they are all of the same size, there being no appreciable difference between the sterile and LE fh fertile ones. The characteristic fo sé Ap club is not present here, but the g SSS 5 spore-cases occupy certain regions of the stem, as shown at 239. Ina YY; AN single season one region of the stem § a” may bear spore-cases, and then a ks sterile portion of the same stem is eran loped, which later b h ex copodium lucidulum, bulbils in axils of developed, which later bears another eaves near the top, sporangia in axils of leaves series of spore-cases highe below them. At right is a bulbil enlarged. Sao eer, 390. Bulbils on Lycopodium lucidulum.—There is one curious way in which this club moss multiplies. One may see frequently among the upper leaves small wedge-shaped or heart- shaped green bodies but little larger than the ordinary leaves, These are little a LITTLE CLUB MOSSES. 193 buds which contain rudimentary shoot and root and several thick green leaves, When they fall to the ground they grow into new lycopodium plants, just as the bulbils of cystopteris do which were described in the chapter on ferns, 891. Note.—The prothallia of the species of lycopodium which have been studied are singular objects. In L. cernuum a cylindrical body sunk in the earth is formed, and from the upper surface there are green lobes, In L. phlegmaria and some others slender branched, colorless bodies are formed which according to Treub grow as a saphrophyte in decayed bark of trees. Many of the prothallia examined have a fungus growing in their tissue which is supposed to play some part in the nutrition of the prothallium. The little club mosses (selaginella). 392. Closely related to the club mosses are the selaginellas. These plants resemble closely the general habit of the club mosses, but are generally smaller and the leaves more delicate. Some species are grown in conservatories for ornament, the leaves of Fig. 240. Fig. 241. Fig. 242. Fig. 243. Selaginella with Fruiting spike Large spo- Small spo- three fruiting spikes. showing large and rangium. rangium. (Selaginella apus.) small sporangia. such usually having a beautiful metallic lustre. The leaves of some are arranged as in lycopodium, but many species have the leaves in four to six rows. Fig. 240 represents a part of a selaginella plant (S. apus). The fruiting spike possesses similar leaves, but they are shorter, and their arrangement gives to the spike a four- sided appearance. 194 MORPHOLOG Y. 393. Sporangia.—On examining the fruiting spike, we find as in lycopodium that there is but a single sporangium in the axil of a fertile leaf. But we see that they are of two different kinds, small ones in the axils of the upper leaves, and large ones in the axils of a few of the lower leaves of the spike. The mzcro- spores are borne in the smaller spore-cases and the macrospores in the larger ones. Figures 241-243 give the details. There are many microspores in a single small spore-case, but 3-4 ma- crospores in a large spore-case. 394. Male prothallia.—The prothallia of selaginella are much reduced structures. The microspores when mature are already divided into two cells. When they grow into the mature pro- thallium a few more cells are formed, and some of the inner ones form the spermatozoids, as seen in fig. 244. Here we see that Fig. 244. Details of microspore and male prothallium of selagine!la; rst, microspore ; 2d, wall re- moved to show small prothallial cell below; 3d, mature male prothallium still within the wall; 4th, small cell below is the prothallial cell, the remainder is antheridium with wall and four sperm cells within; 5th spermatozoid. After Beliaieff and Pfeffer. the antheridium itself is larger than the prothallia. Only an- theridia are developed on the prothallia formed from the microspores, and for this reason the prothallia are called male prothallia. In fact a male prothallium of selaginella is nearly all antheridium, so reduced has the gametophyte become here. 395. Female prothallia.—The female prothallia are devel- oped from the macrospores. The macrospores when mature have a rough, thick, hard wall. The female prothallium begins to develop inside of the macrospore before it leaves the sporangium. The protoplasm is richer néar the wall of the spore and at the LITTLE CLUB MOSSES. 195 upper end. Here the nucleus divides a great many times, and finally cell walls are formed, so that a tissue of considerable ex- tent is formed inside the wall of the spore, which is very different from what takes place in the ferns we have studied. As the prothallium matures the spore is cracked at the point where the three angles meet, as shown in fig. 246. The archegonia are developed in this exposed surface, and several can be seen in the illustration. 396. Embyro,—After fertilization the egg divides in such a way that along cell called « suspensor is cut off from the upper side, Fig. 245. : Section of mature macrospore Mature female prothallium of Fig. 247- of selaginella, showing female selaginella, just bursting open Seedling of sela- prothallium and archegonia, the wall of macrospore, exposing ginella still attached After Pfeffer. archegonia. After Pfeffer. to the macrospore. After Campbell. which elongates and pushes the developing embyro down into the center of the spore, or what is now the female prothallium. Here it derives nourish- ment from the tissues of the prothallium, and eventually the root and stem emerge, while a process called the ‘‘ foot ’’ is still attached to the prothallium, When the root takes hold on the soil the embyro becomes free. € in Vig. 248. CHAPTER XXIX. QUILLWORTS (ISOETES). 397. The quillworts, as they are popularly called, are very curious plants. They grow in wet marshy places. They receive their name from the supposed resemblance of the leaf to a quill. Fig. 248 represents one of these ,quillworts (Isoetes engelmannii). / The leaves are the prominent part of the plant, and they are about all that can be seen except the roots, without removing the leaves, Each leaf, it will be - seen, is long and needle-like, ex- cept the basal part, which is expanded, not very unlike, in out- line, a scale of an onion. These expanded basal portions of the leaves closely overlap each other, and the very short stem is com- pletely covered at all times. Fig. 250 is from a longitudinal sec- tion of a quillwort. It shows the form of the leaves from this view (side view), and also the Tsoetes, mature plant, sporophyte stage. general outline of the short stem, which is triangular, The stem is therefore a very short object. 196 QUILLWORTS. 197 398. Sporangia of isoetes.—If we pull off some of the leaves of the plant we see that they are somewhat spoon-shaped as in fig. 249. In the inner surface of the expanded base we note a circular depression which seems to be of a different text- Fig. 244 Fig. 250. Base of leaf of isoetes, Section of plant of Isoetes engelmanii, showing cup- showing sporangium with shaped stem, and longitudinal sections of the sporan- macrospores. (Isoetes en- gia in the thickened bases of the leaves. gelmannii.) ure from the other portions of the leaf. This is a sporangium. Beside the spores on the inside of the sporangium, there are strands of sterile tissue which extend across the cavity. This is peculiar to isoetes of all the members of the class of plants to which the ferns belong, but it will be remembered that sterile strands of tissue are found in some of the liverworts in the form of elaters. 899. The spores of isoetes are of two kinds, small ones (microspores) and large ones (macrospores), so that in this respect it agrees with selaginella, though it is so very different in other respects. When one kind of spore is borne in a sporan- 198 MORPHOLOG Y. gium usually all in that sporangium are of the same kind, so that certain sporangia bear microspores, and others bear macrospores. But it is not uncommon to find both kinds in the same sporan- gium. When a sporangium bears only microspores the number is much greater than when one bears only macrospores. 400. If we examine some of the microspores of isoetes we see that they are shaped like the quarters of an apple, that is they are of the bilateral type as seen in some of the ferns (asplenium). 401. Male prothallia.—lIn isoetes, as in selaginella, the microspores de- velop only male prothallia, and these are very rudimentary, one division of the spore having taken place before the spore is mature, just as in selagi- nella. 402. Female prothallia.—These are developed from the macrospores. The latter are of the tetrahedral type. The development of the female prothal- lium takes place in much the same way as in selaginella, the entire prothal- lium being enclosed in the macrospore, though the cell divisions take place after it has left the sporangium. When the archegonia begin to develop the macrospore cracks at the three angles and the surface bearing the arche- gonia projects slightly as in selaginella. Absorbing organs in the form of rhizoids are very rarely formed. 403. Embryo.—The embryo lies well immersed in the tissue of the pro- thallium, though there is no suspensor developed as in selaginella. CHAPTER XXX. COMPARISON OF FERNS AND THEIR RELATIVES. 404. Comparison of selaginella and isoetes with the ferns.—On compar- ing selaginella and isoetes with the ferns, we see that the sporophyte is, as in the ferns, the prominent part of the plant. It possesses root, stem, and leaves. While these plants are not so large in size as some of the ferns, still we see that there has been a great advance in the sporophyte of selagi- nella and isoetes upon what exists in the ferns. There is a division of labor between the sporophylls, in which some of them bear microsporangia with microspores, and some bear macrosporangia with only macrospores. In the ferns and horsetails there is only one kind of sporophyll, sporangium, and spore ina species. By this division of labor, or differentiation, between the sporophylls, one kind of spore, the microspore, is compelled to form a male prothallium, while the other kind of spore, the macrospore, is compelled to form a female prothallium. This represents a progression of the sporophyte of a very important nature. 405. On comparing the gametophyte of selaginella and isoetes with that of the ferns, we see that there has been a still farther retrogression in size from that which we found in the independent and large gametophyte of the jiverworts and mosses. In the ferns, while it is reduced, it still forms rhizoids, and leads an independent life, absorbing its own nutrient materials, and assimilating carbon. In selaginella and isoetes the gametophyte does not escape from the spore, nor does it form absorbing™ organs, nor develop assimilative tissue. The reduced prothallium develops at the expense of food stored by the sporophyte while the spore is developing. Thus, while the gametophyte is separate from the sporophyte in selaginella and isoetes, it is really dependent on it for support or nourishment. 406. The important general characters possessed by the ferns and their so-called allies, as we have found, are as follows: The spore-bearing part, which is the fern plant, leads an independent existence from the prothallium, and forms root, stem, and leaves. The spores are borne in sporangia on the leaves. The prothallium also leads an independent existence, though in isoetes and selaginella it has become almost entirely dependent on the sporo- 199 200 MORPHOLOGY. phyte. The prothallium bears also well-developed antheridia and arche- gonia. The root, stem, and leaves of the sporophyte possess vascular tissue. All the ferns and their allies agree in the possession of these char- acters. The mosses and liverworts have well-developed antheridia and archegonia, and the higher plants have vascular tissue. But no plant of either of these groups possesses the combined characters which we find in the ferns and their relatives. The latter are, therefore, the fern-like plants, or pteridophyla. The living forms of the pteridophyta are classified as fol- lows into families or orders. 407. Pteridophyta. Ophioglossacee. Marattiacez. ? Heterosporous (Isoetaceze (Isoetes). Osmundacez. Schizzeacee. ae Gleicheniacez. Class I. Filicales. Hymenophyl- laceze. Cyatheaceze. Polypodiaceee. Polypodium, Ono- Leptosporangiatz. clea, Aspidium, etc: Salviniaceze. Marsiliaceze. Eusporangiate.... | Peano geen | Homosporous. Ifeterosporous. | az Equisetacez. Class II. Equisetales. | cea Lycopodiaceze (Lycopodium). Hompeperons: | Psilotaceze (tropical forms). Class III. Lycopodiales. Heterosporous. (Selaginellaceze (Selaginella). 201 COMPARISON OF PTERIDOPHYTA. aydydorods a *eisuer uo juspuadap| ‘ummduniods ur [[us -odsosowur 1e9q *sauo ‘dia) ‘sprozopeutods! pure umrsurtods apa [jaa puaipjur gaddn ‘vZuer0dso19 ae Re anal Dee ented wa is, Ons paypue ‘yao pear’ sarodsosoeyy foot ts urey!-vun avaq samo amo CEL TEMOIe, ae HPUIOAC -copaAa(y] _ auc [Peus oyu padopaaag | ie -uod sau0 sain ayids ‘ ur ways a SuTaeToS ‘ssajdo]09 “| VAO a Buys ULY ATL] -aj ‘sauv oB1v'| [open ‘sauo [peuy : 7 . a ‘ + ‘ © ‘sasodsosot] |‘ +" *UIe}UOD saUO Pua aq] UO padnoid wy sdofs? sab a vuod|yo nu Wen Ep ts “spury omy, ‘May jpeuy) spupy omy sarvoy Turmwaq-arods |-jaaacy) ‘33a/PUOTP MPT FEUER 9UCO hing go ‘sproznya ou Gem arods yo apis} vaTAN jo BSuviody |yeay ‘ways Yoo {poz nay ‘vypey ord yuasayip uc) “M1 S]]O9 JO ssLUT papuno. ‘ssapo[os ANV IAS avdydosods) -erduriodsoso1ur “splozoy ei) wo arousosseu) “wniguesods ut [pas souo zauut ‘er3uesods +839 )-sods YIM Wunpl tur paroys yuaMIL ayn [jo puayyue! -o19 BU xvaq. 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UWA oes fumiy|-ayy ay [pA enue wor pado/pue Yao peypeyyoud soaodsosouyy | ttt tts s+ ung}saavay ayo | aseq “peqjord opeway|peypeqqed a pAAA(T — ‘aypVusay/[peurs oyur padojaar | -uoo sauo asivy [ye soniavo ur wiSaer] (-yuejd saya]'SSPHO[09 “TeAgiayy uv do sauo adavy frayvu ‘sauo qpeug ‘sasodsoso1 yy ureyu09 souol-ods | yvaq ‘sadvay|-ost ojut sdo|5® xodv uy ‘vpuod MODE et LDL SpULy OMT, *maz ynq 40 ‘spioz feuy "spappomy| yao ys Ara wayg]-podacy) “SsalP UAE MFT FEBUE AUC) lau ou ATpensn “q[vm axods yo opisut yo eSuewds $f yeop ‘arays yooy, | jpaztyq4ay| vey road yuasaypip ucy ‘s][ao Jo Ssvut papunos ‘ssafs0[07) “SaLUOS] “339 uv YIM *splozoyvlu ‘satodg |> terres suey yora ‘eypeqpoad|-sads yy erp eyy, -uoo unuriody (quezd canjas! 12s sasuey uol-ord ayeut [pews “‘pury a u0 yo -mbaojut sdo vigosgayoty luo ‘erpuaiyuy UY syxydoaods -peaaqq) *B3a “eypeqioad yua “splozuys Yi “ty Mo1d uo widurtody *yeal ‘ways “JOOY, | paztypyaoy -layip Uo spury OM} 04} AT[ensq. |paqo, ‘papuedxa ‘uryy ‘uaaid vy WALASINOS, -sorode [++ *streyu03 wnt (juryd “339 IM Yyove| *sprozoyzwutads : -uviody “puny Uday Oyu Sb ‘eluodayory [yy vIpiioyyy, (swaovip auo joy yey -pada{) "saa untpeyyoad “sploziypr yim “Mod padeys -oddjog) uo wSuesody ‘yea ‘uiays Qooy— |pazynsayy auies dy} UO spuly yOg Ayyens~ |-yavay ‘papuedxe ‘funy ‘usa y ‘SNAG | : “ALAM BV ‘LUV AAILVLAOAA | -ONOdS JO “SNVDYQ TVNXAS “LUV DMLV LION A PATE Al ONINNIDTET SEOY | (teaser plea een ees Caykydosods ayy uo yuapuadep Sururosaq saqza0st “HWVE) tO) JAP at0lul PUB J Le ed “Abipue vypouisejas uy “juapuadapur Aysour “aaq;ews Burwosa “ ONINNIDEYL [yuEyd aqy jo ped sade) sLLAHdONOdS Pp TEUOeL I a Potent I f d) “ALAHAOLANVS ‘SALANGOUDELLI SILL NI SLAMIdOWOdS UNV ALAUCOLANVO JO NOLLVIAM ONIMOHS WIVL ‘80 CHAPTER XXXI. GYMNOSPERMS. The white pine. 409. General aspect of the white pine.—The white pine (Pinus strobus) is found in the Eastern United States. In favorable situations in the forest it reaches a height of about 50 meters (about 160 feet), and the trunk a diameter of over 1 meter. In well-formed trees the trunk is straigkt and towering; the branches where the sunlight has access and the trees are not crowded, or are young, reaching out in graceful arms, form a pyramidal outline to thetree. In oldand dense forests the lower branches, because of lack of sunlight, have died away, leaving tall, bare trunks for a considerable height. 410. The long shoots of the pine.—The branches are of twokinds. Those which we readily recognize are the long branches, so called because the growth in length each year is considerable. The terminal bud of the long branches, as well as of the main stem, continues each year the growth of the main branch or shoot; while the lateral long branches arise each year from buds which are crowded close together around the base of the terminal bud. The lateral long branches of each year thus appear to be ina whorl. The distance between each false whorl of branches, then, represents one year’s growth in length of the main stem or long branch. 411. The dwarf shoots of the pine.—The dwarf branches are all lateral on the long branches, or shoots. They are scattered over the year’s growth, and each bears «a cluster of five long, needle-shaped, green Icaves, which remain on the tree for several years. At the base of the grven leaves are anumber of chaff-like scales, the previous bud scales. While the dwarf branches thus bear green leaves, and scales, the long branches bear only thin scale-like leaves which are not green. 202 GYMNOSPERMS.: WHITE PINE, 203 412. Spore-bearing leaves of the pine.—The two kinds of spore-bearing leaves of the pine, and their close relatives, are so different from anything which we have yet studied, and are so unlike the green leaves of the pine, that we would scarcely recognize them as belonging to this category. Indeed there is great uncertainty regarding their origin. 418. Male cones, or male flowers.—The male cones are borne in clusters as shown in fig. 251. Each compact, nearly cylindri- Fig. 251. Spray of white pine showing cluster of male cones just before the scattering of the pollen. cal, or conical mass is termed a cone, or flower, and each arises in place of a long lateral branch. One of these cones is shown 204 ° MORPHOLOGY. considerably enlarged in fig. 252. The central axis of each cone is a lateral branch, and belongs to the stem series. The stem axis of the cone can be seen in fig. 253. It is completely covered by stout, thick, scale-like outgrowths. These scales are obovate in outline, and at the inner angle of the upper end Fig. 252. Fig. 253. Fig. 254. Staminate cone of white Section of staminate Two sporo- pine, with bud scales re- cone, showing sporangia. phylls removed, moved on one side. showing open- ing of sporangia. there are several rough, short spines. They are attached by their inner lower angle, which forms a short stalk or petiole, and continues through the inner face of the scale as a ‘‘ mid- rib.’? What corresponds to the lamina of the scale-like leaf bulges out on each side below and makes the bulk of the scale. These prominences on the under side are the sporangia (micro- sporangia). There are thus two sporangia on a sporophyll (microsporophyll). When the spores (microspores), which here are usually called pollen grains, are mature each sporangium, or anther locule, splits down the middle as shown in fig. 254, and the spores are set free. 414. Microspores of the pine, or pollen grains.—A mature pollen grain of the pine is Fig. 255. : : 8 é Pollen’ grain of Shown in fig. 255. It is a queer-looking object, white pine. - “ 3 possessing on two sides an air sac, formed by the upheaval of the outer coat of the spore at these two points. GYMNOSPERMS: WHITE PINE. 205 When the pollen is mature, the moisture dries out of the scale (or stamen, as it is often called here) while ‘it ripens. When a limb, bearing a cluster \ \ y of male cones, is jarred by the hand, or by i currents of air, the split suddenly opens, and \We a cloud of pollen bursts out from the numer- Wil ous anther locules. The pollen is \ thus borne on the wind and some of it falls on the female flowers. Fig. 256. White pine, branch with cluster of mature cones shedding the seed. A few young cones four months old are shown on branch at the left. Drawn from photograph. 415. Form of the ma- ture female cone.—A cluster of the white- ~ pine cones is shown in S’ fig. 256. These are mature, and the scales have spread as they do when mature and becoming dry, in order that the seeds may be set at liberty. The general out- Mature cone of white pine at time of scattering of the seed, nearly natural size. 206 MORPHOLOGY. line of the cone is lanceolate, or long oval, and somewhat curved. It measures about 1o-15cm long. If we remove one Fig. 258. Fig. 259. Fig. 260. Fig. 261. Fig. 262. Sterile scale. Scale with Seeds have Back of scale Winged Seeds undevel- well-developed split off from with small cover seed free from oped. seeds. scale. scale. scale. Figs. 258-262.—White pine showing details of mature scales and seed. of the scales, just as they are beginning to spread, or before the seeds have scattered, we shall find the seeds at- tached to the upper surface at the lower end. There are two seeds on each scale, one at each lower angle. They are ovate in outline, and shaped somewhat likea biconvex lens. At this time the seeds easily fall away, and may be freed by jarring the cone. As the seed is detached from the scale a strip of tissue from the latter is peeled off. This formsa ‘‘ wing ”’ for the seed. It is attached to one end and is shaped something like a knife blade. On the back of the scale is a small appendage known as the cover scale. 416. Formation of the female pine cone.—The female flowers begin their development rather late in the spring of the year. They are formed from terminal buds of the higher branches of the tree. In this way the cone may terminate the main shvot of a branch, or of the lateral shoots ina whorl. Alter growth has proceeded Female cones of the for some time in the spring, the terminal portion begins pine at time of pollina- : tion, about natural size. to assume the appearance of a young female cone or GYMNOSPERMS.: WHITE PINE. 207 flower. These young female cones, at about the time that the pollen is escaping from the anthers, are long ovate, measuring about 6-1omm long. They stand upright as shown in fig. 263. 417. Form of a “scale” of the female flower.—If we remove one of the scales from the cone at this stage we can better study it in detail. It is flattened, and oval in outline, with a staut ‘“‘rib,’’ if it may be so called, running through the middle line and terminating in a point. ‘he scale is in two parts as shown in fig. 266, which is a view of the under side. The small ‘‘ out- growth’’ which appears as an appendage is the cover scale, for while it is smaller in the pine than the other portion, in some of the relatives of the pine it is larger than its mate, and being on the outside, covers it. (The inner scale is sometimes called the ovu- liferous scale, because it bears the ovules. ) 418. Ovules, or macrosporangia, of the pine.—At each of the lower angles of the Fig. 264. Fig. 265. Fig. 266. Section of female cone Scale of white pine with the Scale uf white pine seen of white pine, showing two ovules at base of ovulif- from the outside, showing the young ovules (macrospo- _erous scale. cover scale. rangia) at base of the ovu- liferous scales. scale is a curious oval body with two curved, forceps-like pro- cesses at the lower and smaller end. These are the macro- sporangia, or, as they are called in the higher plants, the ovules. These ovules, as we see, are in the positions of the seeds on the 208 MORPHOLOGY. mature cones. In fact the wall of the ovule forms the outer coat of the seed, as we will later see. 419. Pollination.—At the time when the pollen is mature the female cones are still erect on the branches, and the scales, which during the earlier stages of growth were closely pressed against one another around the axis, are now spread apart. As the clouds of pollen burst from the clusters of the male cones, some of it is wafted by the wind to the female cones. It is here caught in the open scales, and rolls down to their bases, where some of it falls between these forceps-like processes at the E lower end of the ovule. At Fig. 267. Branch of white pine showing young female cones at time of pollination on the ends of the branches, and one-year-old cones below, near the time of fertilization. this time the ovule has exuded a drop of a sticky fluid in this depression between the curved processes at its lower end. The pollen sticks to this, and later, as this viscid substance dries up, it pulls the pollen close up in the depression against the lower GYMNOSPERMS: WHITE PINE. 209 end of the ovule. This depression is thus known as the pollen chamber. ; 420. Now the open scales on the young female cone close up again, so tightly that water from rains isexcluded. What is also very curious, the cones, which up to this time have been standing erect, so that the open scale could catch the pollen, now turn so that they hang downward. This more certainly excludes the rains, since the overlapping of the scales forms a shingled surface. Quantities of resin are also formed in the scales, which exudes and makes the cone practically impervious to water. 421. The female cone now slowly grows during the summer and autumn, increasing but little in size during this time. During the winter it rests, that is, ceases to grow. With the coming of spring, growth commences again and at an accelerated rate. The increase in . ‘ : Fig. 268, size is more rapid. The cone reaches Macrosporangium of pine F . (ovule), z#¢, integument; 7, nu- maturity in September. We thus see cellus; #z, macrospore. ” (After that nearly eighteen months elapse from offmeister.) the beginning of the female flower to the maturity of the cone, and about fifteen months from the time that pollination takes place. 422. Female prothallium of the pine.—To study this we must make careful longitudinal sections through the ovule (better made with the aid of a micro- tome). Such a section is shown in fig. 269. The outer layer of tissue, which at the upper end (point where the scale is attached to the axis of the cone) stands free, is the ovular coat, or zz¢egument. Within this integument, near the upper end, there is a cone-shaped mass of tissue, which farther down continues along next the integument in a thinner strip. This mass of tissue is the zucellus, or the macrosporangium proper. The elliptical mass of tissue within this, shown in fig. 271 is the female prothallium, or what is usually here called the endosperm. The conical portion of the nucellus fits over the 210 MORPHOLOGY. prothallium, and is called the nucellar cap. Only one end of the endosperm (prothallium) is shown in fig. 271. 423. Archegonia.—In the upper end of the endosperm (prothallium) are several archegonia, and they aid us in determining what portion is the female prothallium. The nucellus is of course formed before the prothallium. The latter arises from a cell (macro- spore) near the center of the nucellus. This cell is larger, and has a larger nucleus than its fellows (see fig. 268). The prothallium here is formed much in the same way as in selaginella, where we recollect it begins to de- velop before the macrospore has ny ok 2 le Fig. 269. Fig. 270. Section of ovule of white pine. 7x¢, integ- | Upper portion of nucellus of white pine. ument; fc, pollen chamber; 77, pollen tube; Ag, pollen-grain remains ; sfc, sperm cells ; n, nucellus; 7, macrospore cavity. vn, vegetative nucleus; #7, pollen tube. reached its full size, and where the archegonia begin to form before it leaves the macrosporangium. : 424. Male prcthallia.—By the time the pollen is mature the male pro- thallum is already partly formed. In fig. 255 we can see two well-formed cells. Other cells are said to be formed earlicr, but they become so flattened that it is difficult to make them out when the pollen grain is mature. At this stage of development the pollen grain is lodged at the mouth of the ovule, and is drawn up into the pollen chamber. 425. Farther growth of the male prothallium.—During the summer and autumn the male prothallium makes some farther growth, but this is slow. The larger cell, called the vegetative cell, elongates by the formation of a tube, furming a sac, known as the pollen tube. It is either simple or branched. Inside of this sac the cells of the prothallium are protected, and farther GYMNOSPERMS: WHITE PINE. 211 division of the cells takes place here, just as the female prothallium develops in the cavity of the nucellus, from the macrospore. The nucleus of the vege- tative cell passes down the cavity of this tubularsac. The antherid cell, which is the smaller cell of the pollen grain, in the pine, divides by a cross wall into a so-called stalk cell, and a mother sperm cell, the latter corresponding to the central cell of the an- Fig. 271. Section through upper part of nucellus and Fig. 272. endosperm of white pine, showing upper por- Last division of the egg in the white tion of archegonium, the entering sperm cells, pine cutting off the ventral canal cell and track of pollen tube; xc, nucellus: /¢, at the apex ofthearchegonium. xd, pollen tube; sfc, sperm cells. endosperm; Arch, archegonium. theridium, there being no wall formed. The sperm mother cell also passes down the tubular sac, and divides again into two sperm cells, as shown in fig. 270. About this time, or rather a little earlier, with the pollen tube part way through the nucellar cap, winter overtakes it, and all growth ceases until the following spring. 426. Fertilization.—In the spring the advance of the pollen tube con- tinues, and it finally passes through the nucellar cap about the time that the archegonia are formed and the egg cell is mature, as shown in fig. 271. The pollen tube now opens and the sperm cells escape into the archegonium, and later one of them fuses with the egg nucleus. The fertilized egg is now ready to develop into the embryo pine. 427. Homology of the parts of the female cone.—Opinions are divided as to the homology of the parts of the female cone of the pine. Some consider the entire cone to be homologous with a flower of the angiosperms. The en- 212 MORPHOLOGY. tire scale according to this view is a carpel, or sporophyll, which is divided into the cover scale and the ovuliferous scale. This division of the sporophy]1 is considered similar to that which we have in isoetes, where the sporophyll Archegonium of Picea Archegonium of Picea) Embryo of Pine seedling just vulgaris, sperm cell ap- vulgaris showing fusion white pine re- emerging from the proaching the nucleus of of sperm nucleus with moved from ground. egg cell. egg nucleus. seed, showing several coty- ledons. Figs. 273, 274.—Fertilization in picea. (After Strasburger.) has a ligule above the sporangium, or as in ophioglossum, where the leaf is divided into a fertile and a sterile portion. A more recent view regards each cone scale as a flower, the ovuliferous scale composed of three united carpels arising in the axil of a leaf, the cover scale. Two of the carpels are reduced to ovules, and the outer integument is expanded into the lateral portion of the scale, while the central carpel is sterile and ends in the point or mucro of the scale. GYMNOSPERMS: WHITE PINE. 213 Fig. 277. White-pine seedling casting seed coats. CHAPTER XXXII. FURTHER STUDIES ON GYMNOSPERMS. Cycas. 428. In such gymnosperms as cycas, illustrated in the front- ispiece, there is a close resemblance to the members of the fern group, especially the ferns themselves. This is at once suggested by the form of the leaves. The stem is short and thick. The leaves have a stout midrib and numerous narrow pinne. In the center of this rosette of leaves are numerous smaller leaves, closely overlapping like bud scales. If we remove one of these at the time the fruit is forming we see that in general it conforms to the plan of the large leaves. There are a midrib anda number of narrow pinne near the free end, the entire leaf being covered with woolly hairs. But at the lower end, in eat ok ies place of the pinne, we see oval bodies. revoluta. These are the macrosporangia (ovules) of cycas, and correspond to the macrosporangia of selaginella, and the leaf is the macrosporophyll. 429. Female prothallium of cycas.—TIn figs. 279, 280 are shown mature ovules, or macrosporangia, of cycas. In 280, which is aroentgen-ray photograph of 279, the oval prothallium can be seen. So in cycas, as in selaginella, the female prothallium is 214 FURTHER STUDIES ON GYMNOSPERMS. 218 developed entirely inside of the macrosporangium, and derives the nutriment for its growth from the cycas plant, which is the Rear eal is Fig. 279. Macrosporangium of Cycas revoluta sporophyte. cells. This aids us in deter- mining that it is the prothal- liunt. In cycas it is also called endosperm, just as in the pines. 430. If we cut open one of the mature ovules, we can see the en- dosperm (prothallium) as a whitish mass of tissue. Immediately sur- rounding it at maturity is a thin, papery tissue, the remains of the nucellus (macrosporangium), and outside of this are the coats of the ovule, an outer fleshy one and an inner stony one. 431. Microspores, or pollen, of cycas.—The cycas plant illustrated in the frontispiece is a female plant. . Male plants also exist which have > ‘oups on the under side. small leaves in the center that bear as sporangia. Fig. 280. Roentgen photograph of same, show- ing female prothallium. Archegonia are developed in this internal mass of Fig. 281. A sporophyll (stamen) of cycas; sporangia in 6, group of sporangia ; (From Warming.) F 2 210 MORPHOLOGY. only microsporangia. These leaves, while they resemble the ordinary leaves, are smaller and correspond to the stamens. Upon the under side, as shown in fig. 281, the microspo- rangia are borne in groups of three or four, and these contain the microspores, or pollen grains, The ar- rangement of these microsporangia on the under side of the cycas leaves bears a strong resemblance to the arrangement of the sporangia on the under side of the leaves of some ferns. : 432. The gingko tree is another very interesting plant belonging to this same group. It is a relic of a genus which i \ | Fig. 282. Zamia inte- grifolia, show- ing thick stem, fern-like leaves, and cone of male flowers. flourished in the remote past, and it is interesting also because of the re- semblance of the leaves to some of the ferns like adiantum, which sug- gests that this form of the leaf in gingko has been inherited from some fern-like ancestor. 433. While the resem- blance of the leaves of someof the gymnosperms to those of the ferns sug- gests fern-like ancestors for the members of this group, there is stronger evidence of such ances- try in the fact that a pro- thallium can well be de- Fig. 283. Two spermiatozeids in end of pollen tube of cycas. (After termined in the ovules. drawing by Hirase and [keno.) The endosperm with its well-formed archegonia is to be considered a prothallium. 434, Spermatozoids in some gymnosperms.—But within the past two years it has been discovered in gingko, cycas, and zamia, all belonging to this FURTHER STUDIES ON GYMNOSPERMS. 217 group, that the sperm cells are well-formed spermatozoids. In zamia each one is shaped somewhat like the half of a biconvex lens, and around the con- vex surface are several coils of cilia. After the pollen tube has grown down through the nucellus, and has reached a depression at the end of the prothallium (endosperm) where the archegonia are formed, the spermatozoids are set free from the pollen tube, swim around in a liquid in this depression, and later fuse with the egg. In gingko and cycas these spermatozoids were first discovered by Ikeno and Hirase in Japan, and later in zamia by Webber in this country. In figs. 283-286 the details of the male prothallia and of fertilization are shown. 435. The sporophyte in the gymnosperms.— In the pollen grains of the gymnosperms we easily recognize the characters belonging to the spores in the ferns and their allies, as well as in Fig. 284. the liverworts and mosses. They belong to the Pskail alt are same series of organs, are borne on the same larger female nucleus of the egg. < ‘ . The egg protoplasm fills the phase or generation of the plant. and are practi- archegonium. (From drawings cally formed in the same general way, the by Hivase and Ikeno.) variations between the different groups not being greater than those within asingle group. These spores we have recognized as being the product of the sporophyte. We are able then to identify the sporophyte as that phase or generation of the plant formed from the fertilized egg and bearing ultimately the spores. We see from this that the sporophyte in the gymnosperms is the prominent part of the plant, just as we found it to be in the ferns. The pine tree, then, Fig 285. as well as the gingko, cycas, yew, hemlock- _ Spermatozoid of gingko, show- spruce, black spruce, the giant redwood of Cali. ing cilia at one end and tail at 2 the other. (After drawings by fornia, etc., are sporophytes. Hirase and Ikeno.) While the sporangia (anther sacs) of the male flowers open and permit the spores (pollen) to be scattered, the sporangia of the female flowers of the gymnosperms rarely open. The macrospore is developed within sporangium (nucellus) to form the female prothallium (endosperm). 436. The gametophyte has become dependent on the sporophyte.— In this respect the gymnosperms differ widely from the pteridophytes, though we see suggestions of this condition of things in isoetes and selaginella, where the female prothallium is developed within the macrospore, and even in sela- ginella begins, and nearly completes, its development while still in the spo- rangium, 218 MORPHOLOGY. In comparing the female prothallium of the gymnosperms with that of the fern group we see « remarkable change has taken place. The female pro- Fig. 286. Gingko biloba. 4, mature pollen grain; 3, germinating pollen grain, the branched tube entering among the cells of the nucellus; 4.x, exine (outer wall of spore); 7, pro- thallial cell; /,, antheridial cell (divides later to form stalk cell and generative cell); /3, vegetative cell; /”a, vacuoles; Ne, nucellus. (After drawings by Hirase and Ikeno.) Fig. 287. thallium of the gymno- sperms is very much reduced in size. Espe- cially, it no longer leads an independent existence from the sporophyte, as is the case with nearly all the fern group. It remains enclosed within the macrosporangium (in cycas if not fertilized it sometimes grows outside of the macrosporangium and becomes green), and derives its nourishment through it from the sporo- phyte, to which the latter remains organically con- nected. This condition of the female prothallium of the gymnosperms necessitated a special adaptation of the male prothallium in order that the sperm cells may reach and fertilize the egg cell. Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche- gonium in the end of the nucellus. 4z, pollen tube; 0, archegonium. (After drawing by Hirase and Ikeno.) 437. Gymnosperms are naked seed plants.—The pine, as we have seen, has naked seeds, That is, the seeds are not enclosed within the carpel, but FURTHER STUDIES ON GYMNOSPERMS. 219 are exposed on the outer surface. All the plants of the great group to which the pine belongs have naked seeds. For this reason the name “‘ gymnosperms” has been given to this great group. 438. Classification of gymno- sperms.—The gingko tree has until recently been placed with the pines, yew, etc., in the class conifer, but the discovery of the spermatozoids in the pollen Fig. 288. Fig. 289. hin Spermatozoids of Spermatozoid of zamia tube suggests that it is mot zamia in pollen tube showing spiral row of closely allied with the coniferz, eae ae chia (Alter Webber) and that it represents a class | Webber.) coordinate with them. Engler arranges the living gymnosperms as follows : Class 1. Cycadales; family Cycadaceze. Cycas, zamia, etc. Class 2. Gingkoales ; family Gingkoacee. Gingko. Class 3. Coniferze; family 1. Taxaceee. Taxus, the common yew in the eastern United States, and Torreya, in the western United States, are examples. family 2, Pinaceee, Araucaria (redwood of California), firs, spruces, pines, cedars, cypress, etc, Class 4. Gnetales. Welwitschia mirabilis, deserts of southwest Africa ; Ephedra, deserts of the Mediterranean and of West Asia. Gnetum, climbers (Lianas), from tropical Asia and America. MORPHOLOG Y. [ juowmsayuy SUT[PIUNT wuadsopusy oCquyy ‘yUBUMSa}UI puv snypeonu ut o5 ssnypeonu ut tutodsopug “(snypaonu ur sutewtas) wiadsopua pue oes-odiquia sdopaa -ap YA snjfaonu jo 19]UId Ut [[90 asIe'T ‘gTNao = jusNSajut Aq potaaod snjpoonyy *(aTBOS I9A09 Fo [Ixe ut) ayays eto yeUID ay} ‘aywos snorayITNAo oyur peytun sjadivo aarq) Io {(qMo0.18yno Areqjedies pue ayeos 12009) afeos snorajtpnacG, *s[[29 dATBIOUES IO ‘s][oo [eULaIe pa0ag "[[29 saneiauery “ureas uaqjod jo [[ao [pews surers uazjod Jo [Jao aatyejada A. ‘uread uatjod oanjeyy ‘ureads uaT[Og ‘ows UdT[Og UOUR}S *SoUOD o[VUa} puv [ey ‘99K JUL “SNNAT NOWIVOD Mell ll WU Ul Hl = ekydorods plo jo Mors Mou Aq papunowny umisuviods puy ayfydojaures jo sureutat uy ayhydosods Suno . ay4ydorods Suno (paztpatey) 533 B34 (suvSi0 [enxas opeway) vruosoyoiy (umiSuvasods ur) umrppeyjord ayeuray (wintsuviods ut sureutar) o10dsor9 eq juommsajut Aq paroaos wnisuesodso1e yy tAydorodsoxsv py s]jao wuods oa} WAOJ O} SaPlAIPp UMIpPLIayjUR Jo [Jao [eNUasy = (ued.10 [vnxas a] RW) LANIPLIayjuUe Jo [[a9 [eyUed Ul Ul He Ww pUR [[99 Y[eIS WO] 0} Saprarp [[A9 WMIPLAqWy ][29 waIprayey (¢ [pea umIpiiaqjue jo yred) [90 adawy UINIPLayyue Are} uatIpnt YIM wMIpeEqy -oid ayem Arejuaumpns st a1odsoxo1ur ammyeyy +++++3}hqdorods Suno | + *‘ayhydojoueds spews Le eeseeeee ++ agfqdorods rocco ‘aykydojoues opeyy artodsoro1yy | umrisuviodso11y yy yAydorodsorstyy yied Surmaq-ai0dy aydydotody : So:ac% teres essay Kudosodg “SULAHAOCINALG NI GaSA ASOHL OL ONIGNOdSANNOD SNA, “ANId AHL NI ALAHAOLANVS UNV ALAHdMOUOdS JO SHIDOTOWOH ONIMOHS ATAVL ‘6 Ep CHAPTER XXXIII. MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA. Trillium. 440. General appearance.—.\s one of the plants to illustrate this group we may take the wake-robin, as it is sometimes called, or trillium. There are several species of this genus in the United States; the commonest one in the eastern part is the ‘«white wake-robin’’ (‘Trillium grandiflorum). This occurs in or near the woods. A picture of the plant is shown in fig. 290. There is a thick, fleshy, underground stem, or rhizome as it is usually called. This rhizome is perennial, and is marked by ridges and scars. The roots are quite stout and possess coarse wrinkles. From the growing end of the rhizome each year the leafy, flowering stem arises. This is 20—30cm (8--12 inches) in height. Near the upper end is a whorl of three ovate leaves, and from the center of this rosette rises the flower stalk, bearing the flower at its summit. 441. Parts of the flower. Calyx.—Now if we examine the flower we see that there are several leaf-like structures. These are arranged also in threes just as are the leaves. First there is a whorl of three, pointed, lanceolate, green, leaf-like members, which make up the ca/yx in the higher plants, and the parts of the calyx are sepa/s, that is, each leaf-like member is a sepal. But while the sepals are part of the flower, so called, we easily recognize them as belonging to the /ea/ series. 222 MORPHOLOGY. 442. Corolla.—Next above the calyx is a whorl of white or pinkish members, in are also leaf-like in form, being usually somewhat make up what is the and each member of the they are parts of the form and_ posi- also belong to the leaf 443. Andrecium. — tion of the corolla is of members which do not They are known their form. As seen in fig. 291 each ament), and extending greater part of the length side. This part of the ridges form the anther Soon after the flower is ther sacs open also by a along the edge of the time we see quantities of or dust escaping from the — Trillium grandiflorum. locules. Trillium grandiflorum, which and broader than the sepals, broader at the free end. These corolla in the higher plants, corolla is a fefal. But while flower, and are not green, tion would suggest that they series. Within and above the inser- found another tier, or whorl, at first sight resemble leaves in in the higher plants as s/amens. stamen possesses a stalk (= fil- along on either side for the are four ridges, two on each stamen is the az/her, and the sacs, or lobes. opened, these an- split in the wall ridge. At this end yellowish powder ruptured anther If we place some of this under the microscope we see ANGIOSPERMS: TRILLIUM. 223 that it is made up of minute bodies which resemble spores ; they are rounded in form, and the outer wall isspiny. They are in fact spores, the microspores of the trillium, and here, as in the gymnosperms, are better known as pollen. Fig. 291. Sepal, petal, stamen, and pistil of Trillium grandiflorum. 444, The stamen a sporo- phyll.—Since these pollen grains are the spores, we would infer, from what we have learned of the ferns and gym- nosperms, that this member of the flower which bears them is a sporophyll ; and this is the case. It is in fact what is called the microsporophill. Then we see also that the anther sacs, since they enclose the spores, would be the sporangia (microsporangia). From ‘this it is now quite clear that the stamens belong also to the leaf series. ‘They Gity are just six in number, twice the number — found in a whorl of leaves, or sepals, or corolla. It is believed, therefore, that there are two whorls of stamens in the flower of trillium. 445. Gynecium.—Next above the stamens and at the center of the flower is a stout, angular, ovate body which terminates in three long, slender, curved points. This is the pistil, and at Fig. 292. Trillium gran- 4 diflorum, with i the compound pistil expanded Wj into three leaf- like members. At the right these three are shown in detail. 224 MORPHOLOGY. present the only suggestion which it gives of belonging to the leaf series is the fact that the end is divided into three parts, the number of parts in each successive whorl of members of the flower. If we cut across the body of this pistil and examine it with a low power we see that there are three chambers or cavi- ties, and at the junction of each the walls suggest to us that this body may have been formed by the y : infolding of the margins of three leaf-like members, the places of contact having then become grown together. We see also that from the incurved margins of each division of the pistil there stand out in the cavity oval bodies. These are the ovules. Now the ovules we have learned from our study of the gymnosperms are the eva ite sporangia (here the macrosporangia). members: It is now more evident that this curious body, the pistil, is made up of three leaf-like members which have fused together, each mem- ber being the equivalent of a sporophyll (here the macrosporo- phyll). This must be a fascinating observation, that plants of such widely different groups and of such different ‘grades of complexity should have members formed on the same plan and belonging to the same Abnormal trillium. The nine parts of the perianth are green, and the outer whorls of stamens are series of members, devoted to similar functions, and yet carried out with such great modifications that at first we do not see this. common meeting ground Fig. 294. which a comparative study brings out so clearly. ‘Transformed stamen of tu 446. Transformations of the flower of trillium.— zetia Agee If anything more were needed to make it clear that on the margin. the parts of the flower of trillium belong to the leaf series we could obtain evidence from the transformations which ANGIOSPERMS: DENTARIA. 225 the flower of trillium sometimes presents. In fig. 293 is a sketch of a flower of trillium, made from a photograph. One set of the stamens has expanded into petal-like organs, with the anther sacs on the margin. In fig. 292 is shown a plant of Trillium grandiflorum in which the pistil has separated into three distinct and expanded leaf-like structures, all green except portions of the margin. Dentaria. 447. General appearance.—For another study we may take a plant which belongs to another division of the higher plants, the common ‘‘ pepper root,’’? or ‘‘toothwort’’ (Dentaria diphylla) as it is sometimes called. This plant occurs in moist woods during the month of May, and is well distributed in the northeastern United States. A plant is shown in fig. 295. It has a creeping underground rhizome, whitish in color, fleshy, and with a few scales. Each spring the annual flower-bearing stem rises from one of the buds of the rhizome, and after the ripening of the seeds, dies down. The leaves are situated a little above the middle point of the stem. They are opposite and the number is two, each one being divided into three dentate lobes, making what is called a compound leaf. 448. Parts of the flower.—The flowers are several, and they are borne on quite long stalks (pedicels) scattered over the ter- minal portion of the stem. We should now examine the parts of the flower beginning with the calyx. This we can see, look- ing at the under side of some of the flowers, possesses four scale- like sepals, which easily fall away after the opening of the flower. They do not resemble leaves so much as the sepals of trillium, but they belong to the leaf series, and there are two pairs in the set of four. The corolla also possesses four petals, which are more expanded than the sepals and are whitish in color. The sta- mens are six in number, one pair lower than the others, and also 226 MORPHOLOGY. shorter. The filament is latter consisting of two lobes or sacs, instead of four as in trillium. The pistil is composed of two carpels, or leaves fused together. So we find in the case of the pepper root that the parts of the flower are in twos, or multiples of two. Thus they agree in this respect with the leaves; and while we do not see such astrong resem- @& blance between the parts of the flower here and the leaves, yet from the pres- ence of the pollen long in proportion to the anther, the Fig. 296. Flower of the toothwort (Dentaria diphylla). Toothwort (Dentaria diphylla). ANGIOSPERMS: DENTARIA. 227 (microspores) in the anther sacs (microsporangia) and of ovules (macrosporangia) on the margins of each half of the pistil, we are, from our previous studies, able to recognize here that all the members of the flower belong to the leaf series. 449. In trillium and in the pepper root we have seen that the parts of the flower in each apparent whorl are either of the same number as the leaves in a whorl, or some multiple of that num- ber. This is true of a large number of other plants, but it is not true of all. A glance at the spring beauty (Claytonia virginiana, fig. 349) and at the anemone (or Isopyrum biternatum, fig. 355) will serve to show that the number of the different members of the flower may vary. ‘The trillium and the dentaria were selected as being good examples to study first, to make it very clear that the members of the flower are fundamentally leaf structures, or rather that they belong to the same series of members as do the leaves of the plant. CHAPTER XXXIV. GAMETOPHYTE AND SPOROPHYTE OF ANGIO- SPERMS. 450. Male prothallium of angiosperms.—The first division which takes place in the nucleus of the pollen grain occurs, in Fig. 297. Nearly mature ollen grain of tril- ium. ‘The smaller cell is the genera- tive cell. young pollen the mother cell. grain is shown in fig. the case of trillium and many others of the angio- sperms, before the pollen grain is mature. case of some specimens of T. grandiflorum in which the pollen was formed during the month of October of the year before flowering, the divi- sion of the nucleus into two nuclei took place soon after the formation of the four cells from The nucleus divided in the In the 297. After this takes place ‘the wall of the pollen grain becomes stouter, and minute spiny projections are formed. 451. The larger cell is the vegetative cell of the prothallium, while the smaller one, since it later forms the sperm cells, is the generative cell. This gencrative cell then corresponds to the central cell of the antheridium, and the vegetative cell perhaps corresponds to a wall cell of the antheridium. If this is so, then the male prothallium of angiosperms has become reduced to a very simple antheridium. The further growth takes place after fertilization. In some plants the generative cell divides into the two sperm cells at the maturity of the pollen grain. In other cases the geucrative after the germination of the pollen grain. Fig. 298. Germinating spores (pollen eae) ot pel- tandra; generative Dee 3 in one undi- vided, in other divided to form the two ‘Sperm nuclei; vegetative nu- cleus in each near the pollen grain. cell divides in the pollen tube For study of the pollen tube the pollen may be germinated in a weak solution of sugar, or on the cut surface 228 GAMETOPHYTE AND SPOROPHYTE. 229 of pear fruit, the latter being kept in a moist chamber to prevent drying the surface. 452. In the spring after flowering the pollen escapes from the anther sacs, and as a result of pollination is brought tv rest on the stigma of the pistil. Here it germinates, as we say, that is it develops a long tube which makes its way down through the style, and in through the micropyle to the embryo sac, where, in accordance with what takes place in other £ plants examined, one of the sperm cells unites with the egg, and fertilization of the egg is the result. 453. Macrospore and embyro sac. three pistils or carpels are united into taria the two carpels are also united carpel. Simple carpels are found in example in the ranunculacez, the bine, etc. These simple carpels beara cy > =f Fig. 299. - AS Section of pistil of trillium, Fig. 300. showing position of ovules Mandrake (Podo- (macrosporangia). phyllum peltatum). —In trillium the one, and in den- into one compound many plants, for buttercups, colum- greater resemblance to a leaf, the mar- gins of which are folded around so that they meet and enclose the ovules or sporangia. 454. If we cut across the com- pound pistil of tril- lium we find that the infoldings of the three pistils meet to form three partial partitions which extend nearly to the center, dividing off three spaces. In these spaces are the ovules which are attached to the infolded margins. If we make cross sections of a pistil of the May- 230 MORPHOLOGY. apple (podophyllum) and through the ovules when they are quite young, we shall find that the ovule has a structure like that shown in fig. 301. At m isacell much larger than the surround- ing ones. This is the macrospore. The tissue surrounding it is called here the nucellus, but because it contains the macrospore it must be the macrosporangium. The two coats or integuments of the ovule are yet short and have not grown out over the end of the nucellus. This macrospore increases in size, forming first a cavity or sac inthe nucellus, the embryo sac. The nucleus divides ¥ rae [=i [av RG TT Fig. jor. Young ovule (macrosporangium) of podophyllum. x, nucellus containing the one-celled stage of the macrospore; 7.7¢, inner integument; 0./¢, outer integument. several times until eight are formed, four in the micropylar end of the embryo sac and four in the opposite end. In some plants it has been found that one nucleus from each group of four moves toward the middle of the embryo sac. Here they fuse to- gether to form one nucleus, the endosperm nucleus or definitive nucleus shown in fig. 302. One of the nuclei at the micropylar end is the egg, while the tvo smaller ones nearer the end are the GAMETOPHYTE AND SPOROPHYTE. 231 synergids. The egg cell is all that remains of the archegonium in this reduced prothallium. are the anfpodal cells. The three nuclei at the lower end Fig. 302. Podophyllum peltatum, ovule containing mature embryo sac; two synergids and egg at left, endosperm nucleus in center, three antipodal cells at right. 455. Embryo sac is the young female prothallium.—In figures 303, 305 are shown the different stages in the develop- ment of the embryo sac in lilium. The embryo sac at this stage is the young female prothallium, and the egg is the only remnant of the femalé sexual organ, the arche- gonium, in this reduced gameto- phyte. 456. Fertilization. — Before fertilization can take place the pollen must be conveyed from the anther to the stigma. (For Macrospore (one-celled stage) of lilium. the different methods of pollination see Part III.) When the pollen tube has reached the embryo sac, it opens and the sperm cell is emptied into the embryo sac near the egg. The sperm nucleus now enters the protoplasm surrounding the egg nucleus. The male nucleus is usually smaller than the female nucleus, and sometimes, as in the cotton plant, it grows to near or quite the 232 MORPHOLOGY. size of the female nucleus before the fusion of the two takes place. In figs. 306 and 307 are shown the entering pollen tube with the sperm nucleus, and the fusion of the male and female nuclei. 457. Fertilization in plants is fundamentally the same as in animals.—In all the great groups of plants as represented by spirogyra, cedogonium, vaucheria, peronospora, ferns, gymno- Fig. 304. Two- and four-celled stage of embryo-sac of lilium. The middle one shows division of nuclei to form the four-celled stage. (Kaster lily.) sperms, and in the angiosperms, fertilization, as we have seen, consists in the fusion of a male nucleus with a female nucleus. Fertilization, then, in plants is identical with that which takes place in animals. 458. Embryo.—After fertilization the egg develops into a short row of cells, the suspensor of the embryo. At the free end the embyro develops. In figs. 309 and 310 is a young embryo of trillium. 459. Endosperm, the mature female prothallium.—During the development of the embryo the endosperm nucleus divides GAMETOPHYTE AND SPOROPAYTE. 233 into a great many nuclei in a mass of protoplasm, and cell walls are formed separating them into cells. ‘This mass of cells is the endosperm, and it surrounds the embryo. It is the ma/ure female prothallium, belated in its growth in the angiosperms, usually de- veloping only when fertilization takes place, and its use has been assured. 460. Seed.—As the embryo Fig. 305. Mature embryo sac (young pro- Section through nucellus and upper part of embryo thallium) of lilium. 7, micropylar sac of cotton at time of entrance of pcllen tube. &, end; S, synergids; £, egg; Px, egg; 5S, synergids; /, pollen tube with sperm cell in polar nuclei; Avzf, antipodals. the end. (Duggar.) (Easter lily.) 234 is developing it derives its in some cases perhaps from the nucellus). Fertilization of cotton. _ pollen tube; Sx, synergids; Z, egg, with male and female nu- cleus fusing. (Duggar.) the integuments increase in extent and harden as the seed is formed. 461. Perisperm. —In most plants the nucellus is all consumed in the devel- opment of the endosperm, so that only minute frag- ments of disorganized cell walls remain next the in- ner integument. Insome plants, however, (the water- lily family, the pepper family, etc.,) a portion of the nucellus remains tact in the mature seed. In such seeds the remain- in- MORPHOLOGY. nourishment from the endosperm (or At the same time pe, Fig. 308. Diagrammatic section of ovary and ovule at time of fertilization in angiosperm. 7, funicle of ovule; n, nucellus; wz, micropyle; 4, antipodal cells of embryo sac; ¢, endosperm nucleus; /#, egg cell and synergids ; a7, outer integument of ovule; 27, inner integument. The track of the pollen tube is shown down through the style, walls of the ovary to the micropylar end of the embryo sac. ing portion of the nucellus is the perzsperm. 462. Presence or absence of endosperm in the seed.—In many of the angiosperms all of the endosperm is consumed by the embryo during its growth in the formation of the seed. This is the case in the rose family, crucifers, composites, willows, oaks, legumes, etc., as in the acorn, the bean, pea and others. In some, as in the bedn, a large part of the nutrient substance pass- GAMETOPHYTE AND SPOROPHYTE. 235 ing from the endosperm into the embryo is stored in the cotyle- dons for use during germination. In other plants the endosperm Fig. 309. Fig. 310. Section of one end of ovule of trillium, showing Embryo en- young embryo in endosperm. larged. is not all consumed by the time the seed is mature. Examples of this kind are found in the buttercup family, the violet, lily, palm, Fig. 311. Fig. 312. Section of fruit of pepper (Piper nigrum), showing small embryo lying in a small quantity of whitish endo- sperm at one end, the perisperm oc- cupying the larger part of the interior, surrounded by pericarp. Seed of violet, external view, and section. The section shows the embryo lying in the endosperm. jack-in-the-pulpit, etc. Here the remaining endosperm in the seed is used as food by the embryo during germination. 463. Sporophyte is prominent and highly developed.—In the angiosperms then, as we have seen from the plants already studied, the trillium, dentaria, 236 MORPHOLOG ¥. etc., are sporophytes, that is they represent the spore-bearing, or sporophytic, stage, Justas we found in the case of the gymnosperms and ferns, this stage is the prominent one, and the one by which we characterize and recognize the plant. We see also that the plants of this group are still more highly special- ized and complex than the gymnosperms, just as they were more specialized and complex than the members of the fern group. From the very simple condition in which we possibly find the sporophyte in some of the alge like spirogyra, vaucheria, and coleochete, there has been a gradual increase in size, specialization of parts, and complexity of structure through the bryo- phytes, pteridophytes, and gymnosperms, up to the highest types of plant structure found in the angiosperms. Not only do we find that these changes have taken place, but we see that, from a condition of complete dependence of the spore-bearing stage on the sexual stage (gametophyte), as we find it in the liverworts and mosses, it first becomes free from the gametophyte in the mem- bers of the fern group, and is here able to lead an independent existence. The sporophyte, then, might be regarded as the modern phase of plant life, since it is that which has become and remains the prominent one in later times. 464. The gametophyte once prominent has become degenerate.—On the other hand we can see that just as remarkable changes have come upon the other phase of plant life, the sexual stage, or gametophyte. There is reason to believe that the gametophyte was the stage of plant life which in early times existed almost to the exclusion of the sporophyte, since the characteristic thallus of the algee is better adapted to an aquatic life than is the spore- bearing’ state of plants. At least, we now find in the plants of this group as well as in the liverworts, that the gametophyte is the prominent stage. When we reach the members of the fern group, and the sporophyte becomes independent, we find that the gametophyte is decreasing in size, in the higher members of the pteri- dophytes, the male prothaliium consisting of only a few cells, while the fe- male prothallium completes its development still within the spore wall. And in selaginella it is entirely dependent on the sporophyte for nourishment. 465. As we pass through the gymnosperms we find that the condition of things which existed in the bryophytes has been reversed, and the gameto- phyte is now entirely dependent on the sporophyte for its nourishment, the female prothallium not even becoming free from the sporangium, which remains attached to the sporophyte, while the remnant of a male prothallium, during the stage of its growth, receives nourishment from the tissues of the nucellus through which it bores its way to the egg-cell. 466. Inthe angiosperms this gradual degradation of the male and female prothallia has reached a climax in a one-celled male prothallium with two sperm-cells, and in the embryo-sac with no clearly recognizable traces of an archegonium to identify it as a female prothallium, The development of the endosperm subsequent, in most cases, to fertilization, providing nourishment CAMETOPHYTE AND SPOROPHYTE. 237 for the sporophytic embryo at one stage or another, is believed to be the last remnant of the female prothallium in plants. 467. Synopsis of members of the sporophyte in angiosperms. Root. { Foliage leaves. Shoot Stem, | Perianth leaves, F Leaf, | Spore-bearing leaves with sporangia. Flower, Sporophyte phase Higher plant. (or modern phase) (Sporangia sometimes on shoot.) MORPHOLOGY. 238 “Pees “sno -nu wiodsopua jo suotstarp Auew fq padojaaap ‘waadsopugq ‘snaponu uadsopua t Suryeur ‘pasny raponu avjod omy, ‘YJao wes Jo ‘][ao peUAayY oes OAIQUIT] ‘oes-oA quia Jo 9}B4s AapONUIU) ‘gynao = s}woo Zz io 1 Aq pataaod ‘snqjaonyy } “AIBA, i jade) aT AS "eUsNS \ tO [Nstd “s][99 daTesauas 10 ‘s]]9O [BUIOyeg raqn} UIA ures UsT[Og *][99 datyerauar) ‘Jao eanejese\, ‘ules UdT[Og “MO} IO OA} ATTENSN ‘es UaT[Og eee f uaweys ‘rayjuy | *sjadieo pu suomeysy ‘yueyd zaystzEy “SIWUMAT, NOWWOD *paas ay} = (7809 1v[NAO puke ‘snyjaonU jO puv wuadsopua jo sureutas) ayAydorods pjo jo syed mou pue ayAydojauivd jo syueuuat Aq papunowns ayAydosods Suno x = syeoo fq papunoums (juasqe aymb 10 Ayawou sretesssesssaykudorods pro Jayep saumpawwos) wiadsopua ut ofaqurq = *okIq ¢ JO WWMOIS Mau pue ayAydoyaured yy -Wd WIOJ 0} Saptarp Bsa ‘dda Jo uoepUNdIy IaIVW J jo syzed Aq papunoumns ay4ydorods suno x, a umtypeyqord o[BUlof IINJE TAL wniypeqoud jo yred Surmoisy S33 ‘umruosayoie jo yuvUay + saydydojaures ayeura.y wunqypeyjoad apeuay | Bunok wioy 0} s[jao g oyur saptatp arodsoroepy i sadavpua Ayavo ‘aay aUIOIdq JOU Sa0p ‘umiBuviodsorsvut jo pus ut ][90 ‘arodsosoeyyl (uedi0 [en ' ‘U-xas avy) Il Il I] syeoo z 10 1 Aq padoaod ‘umisueviodso1e yy SSeS sig Dace Sehr eee eo Koro I yAydorodsore yy i sjjao weds z ‘paprarp [[99 wWnIplayuy | wurypeqjoad ayeur aanjeyy (uvS10 Jenxas ayeut) UMIplayjuE jo [Jao JexyUas ay} st [99 aSrey Jo usejdojord ur Suyeoy “pea ou ‘snopnu yA [Io [EWS "Zz = arods jo [fea Aq popunoums snoponu sj yay “(¢ [pea wMprayjue jo yivd) [Jao asaeT “1 = wnypeyjord ts es oyeut Sunos HW € ro z jo Aqyensn Ayunyeur ye arodsosoryy | = umrsuvs1odsor1yy } i nonsia hares mudinece ses #459 A doqoumEd ew | = dydosodsoro1yq Renee reres “t+ ++ +9fydorodg yied Suttwaq as0dg = ay4ydorodg "SHLAHdAOGINALY NI GSN ASOHL OL ONIANOdSAAAOD SNWAAT, “SWUAdSOIDNV NI ALAHAdOLZNVO AUNV ALAHdONOdS AO SHIDOTIONOH ONIMOHS ATAVL ‘89p CHAPTER XXXV. MORPHOLOGY OF THE NUCLEUS AND SIGNIFI. CANCE OF GAMETOPHYTE AND SPOROPHYTE. 469. In the development of the spores of the liverworts, mosses, ferns, and their allies, as well as in the development of the microspores of the gymnosperms and angiosperms, we have observed that four spores are formed from a single mother cell. These Fig. 313. Fig. 314. Forming spores in mother Spores ust mature and wall of cells (Polypodium vulgare). bier = broken (Asplenium bul- iferum). mother cells are formed as a last division of the fertile tissue (archesporium) of the sporangium. In ordinary cell di- vision the nucleus always divides prior to the division of the cell. In many cases it is directly connected with the laying down of the dividing cell wall. 470. Direct division of the nucleus.—The nucleus divides in two different ways. Onthe one hand the process is very simple. The nucleus simply fragments, or cuts itself in two. This is direct division. 471. Indirect division of the nucleus.—On the other hand very complicated phenomena preéede and attend the division of 239 240 MORPHOLOGY. the nucleus, giving rise to a succession of nuclear figures presented by a definite but variable series of evolutions on the part of the nuclear substance. This is direct division of the nucleus, or karyokinests. Indirect division of the nucleus is the usual method, and it occurs in the normal growth and division of the cell. The nuclear figures which are formed in the division of the mother cell into the four spores are somewhat different from those occurring in vegetative division, but their study will serve to show the general character of the process. 472. Chromatin and linin of the nucleus.—In figure 315 is represented a pollen mother cell of the May-apple (podophyl- Fig. 315. Fig. 316. Fig. 317. Pollen mother cell Spirem stage of nucleus. Forming © spindle, of podophyllum, rest- 2, nuclear cavity; », nu- threads from proto- ing nucleus. Chroma- cleolus; S/, spirem, plasm with several tin forming a_net- poles, roping the work. chromosomes up to (Figures 315-317 after Mottier.) nuclear plate. lum). The nucleus is in the resting stage. There is a network consisting of very delicate threads, the Zim network. Upon this network are numerous small granules, and at the junction of the threads are distinct knots. The nucleolus is quite large and prominent. ‘The numerous small granules upon the linin stain very deeply when treated with certain dyes used in differentiating the nuclear structure. This deeply staining substance is the chromatin of the nucleus. GAMETOPHYTE AND SPOROPHYTE. 241 473. The chromatin skein.—One of the first nuclear figures in the preparatory stages of division is the chromatin sei or spirem. The chromatin substance unites to form this. The spirem is in the form of a narrow continuous ribbon, or band, woven into an irregular skein, or gnarl, as shown in figure 316. This band splits longitudinally into two narrow ones, and then each divides into a definite number of segments, about eight in the case of podophyllum. Sometimes the longitudinal splitting of the band appears to take place after the separation into the chro- matin segments. The segments remain in pairs until they separate at the nuclear plate. 474. Chromosomes, nuclear plate, and nuclear spindle.— Each one of these rod-like chromatin segments is a chromosome. Fig. 318. Karyokinesis in pollen mother cells of pecophyllut, At the left the spindle with the chromosomes separating at the nuclear plate; in the middle figure the chromosomes have reached the poles of the spindle, and at the right the chromosomes are forming the daughter nuclei. (After Mottier.) The pairs of chromosomes arrange themselves in a median plane of the nucleus, radiating somewhat in a stellate fashion, forming the zuclear plate, or monasfer. At the same time threads of the protoplasm (kinoplasm) become arranged in the form of a spindle, the axis of which is perpendicular to the nuclear plate of chromo- somes, as shown in figure 318, at left. Each pair of chromosomes now separate in the line of the division of the original spirem, one chromosome of each pair going to one pole of the spindle, 242 MORPHOLOG Y. while the other chromosome of each pair goes to the opposite pole. The chromosomes here unite to form the daughter nuclei. Each of these nuclei now divide as shown in figure 320 (whether the chromo- somes in this second divi- sion in the mother cell split longitudinally or divide transversely has not been Fipeaae: definitely settled), and four iteet save ia eoperton if “ie! tmclel ame fonmed on the Mother) In podophyllum. pollen mother cell. The protoplasm about each one of these four nuclei now surrounds itself with a wall and the spores are formed. The number of chromosomes usually the same in a given species throughout one phase of the plant.—In those plants which have been carefully studied, the number of chromosomes in the dividing nucleus has been found to be fairly constant in a given species, through all the divisions in that stage or phase of the plant, especially in the embryonic, or young growing parts. For example, in the prothallium, or gameto- phyte, of certain ferns, as osmunda, the number of chromosomes in the divid- ing nucleus is always twelve. So in the development of |- the pollen of lium from the mother cells, and in the divisions of the antherid cell to form the generative Fig. 320. Fig. 321. cells or Spenny cells, there Second division _ of Chromosomes uniting are always twelve chromo- »uclei in pollen mother at poles to form the cell of podophyllum, nuclei of the four spores. somes so far as has been chromosomes at poles. (After Mottier.) found. In the development of the egg of lilium from the macrospore there are also twelve chromosomes. a GAMETOPHYTE AND SPOROPHYTE. 243 When fertilization takes place the number of chromosomes is doubled in the embryo.—In the spermatozoid of osmunda then, as well as in the egg, since these are developed on the game- tophyte, there are twelve chromosomes each. ‘The same is true in the sperm-cell (generative cell) of lilium, and also in the egg- cell. When these nuclei unite, as they do in fertilization, the paternal nucleus with the maternal nucleus, the number of chro- mosomes in the fertilized egg, if we take lilium as an example, is twenty-four instead of twelve; the number is doubled. The fertilized egg is the beginning of the sporophyte, as we have seen. Curiously throughout all the divisions of the nucleus in the em- bryonic tissues of the sporophyte, so far as has been determined, up to the formation of the mother cells of the spores, the number of chromosomes is usually the same 475. Reduction of the number of chromosomes in the nu- cleus.—lIf there were no reduction in the number of chromosomes 7 Fig. 322. Karyokinesis in sporophyte cells of podophyllum (twice the number of chromosomes here that are found in the dividing spore mother cells). at any point in the life cycle of plants, the number would thus become infinitely large. A reduction, however, does take place. 244 MORPHOLOGY. This usually occurs, either in the mother cell of the spores or in the divisions of its nucleus, at the time the spores are formed. In the mother cells a sort of pseudo-reduction is effected by the chromatin band separating into one half the usual number of nu- clear segments. So that in lilium during the first division of the nucleus of the mother cell the chromatin band divides into twelve segments, instead of twenty-four as it has done throughout the sporophyte stage. Soin podophyllum during the first division in the mother cell it separates into eight instead of into sixteen. Whether a qualitative reduction by transverse division of the spirem band, unaccompanied by a longitudinal splitting, takes place during the first or second karyokinesis is still in doubt. Qualitative reduction does take place in some plants according to Beliaieff and others. Recently the author has found that it takes place in Trillium grandiflorum during the second karyoki- nesis, and in Arisaema triphyllum the chromosomes divide both transversely and longitudinally during the first karyokinesis form- ing four chromosomes, and a qualitative reduction takes place here. 476. Significance of karyokinesis and reduction.—The pre- cision with which the chromatin substance of the nucleus is di- vided, when in the spirem stage, and later the halves of the chromosomes are distributed to the daughter nuclei, has led to the belief that this substance bears the hereditary qualities of the organism, and that these qualities are thus transmitted with cer- tainty to the offspring. In reduction not only is the original number of chromosomes restored, it is believed by some that there is also a qualitative reduction of the chromatin, i.e. that each of the four spores possesses different qualitative elements of the chromatin as a result of the reducing division of the nucleus during their formation. The increase in number of chromosomes in the nucleus occurs with the beginning of the sporophyte, and the numerical reduc- tion occurs at the beginning of the gametophyte stage. ‘The full import of karyokinesis and reduction is perhaps not yet known, but there is little doubt that a profound significance is to be attached to these interesting phenomena in plant life. GAMETOPHYTE AND SPOROPHYTE. 245 477. The gametophyte may develop directly from the tissue of the sporophyte.—If portions of the sporophyte of certain of the mosses, as sections of a growing seta, or of the growing capsule, be placed on a moist substratum, under favorable condi- tions some of the external cells will grow directly into protonemal threads. In some of the ferns, as in the sensitive fern (onoclea), when the fertile leaves are expanding into the sterile ones, proto- nemal outgrowths occur among the aborted sporangia on the leaves of the sporophyte. Similar rudimentary protonemal growths sometimes occur on the leaves of the common brake (pteris) among the sporangia, and some of the rudimentary spo- rangia become changed into the protonema. In some other ferns, as in asplenium( A. filix-foemina, var. clarissima), prothallia are borne among the aborted sporangia, which bear antheridia and archegonia. In these cases the gametophyte develops from the tissue of the sporophyte without the intervention or necessity of the spores. This is apospory. 478. The sporophyte may develop directly from the tissue of the gametophyte.—In some of the ferns, Pteris cretica for example, the embryo fern sporophyte arises directly from the tissue of the prothallium, without the intervention of sexual “organs, and in some cases no sexual organs are de- veloped on such prothallia. Sexual organs, then, and the fusion of the spermato- zoid and egg nucleus are not here necessary for the development of the spo- rophyte. This is apogamy. Apogamy occurs in some Bieegaz: other species of ferns, and Apogamy in Pteris cretica. in other groups of plants as well, though it is in general a rare occurrence except in certain species, where it may be the general rule. 246 MORPHOLOGY. 479. Perhaps there is not a fundamental difference between gametophyte and sporophyte.—This development of sporo- phyte, or leafy-stemmed plant of the fern, from the tissue of the gametophyte is taken by some to indicate that there is not sucha great difference between the gametophyte and sporophyte of plants as others contend. In accordance with this view it has been suggested that the leafy-stemmed moss plant, as well as the leafy stem of the liverworts, is homologous with the sporophyte or leafy stem of the fern plant; that it arises by budding from the protenema; and that the sexual organs are borne then on the sporophyte. LESSONS ON PLANT FAMILIES. CHAPTER XXXVI. RELATIONSHIPS SHOWN BY FLOWER AND FRUIT. 480. Importance of the flower in showing kinships among the higher plants.—In the seed-bearing plants which we are now studying we cannot fail to be impressed with the general pres- ence of what is called the flower, and that the flower has its culmi- nating series in the spore-bearing members of the plant (stamens and carpels). Aside from the very interesting comparison of the changes which have taken place in passing from the simple and generalized sporophyte of the liverworts and mosses to the com- plex and specialized sporophyte of the higher plants, we should now seek to interpret the various kinds of aggregations of the spore-bearing members, here termed stamens and carpels. In the part of the book which deals with ecology we shall see how the grouping of these members of the plant is an advantage to it in the performance of those functions necessary for fruition. 481. While the spore-bearing members, as well as the floral envelopes, are thus grouped into ‘‘flowers,’’ there is a great diversity in the number, arrangement, and interrelation of these members, as is suggested by our study of trillium and dentaria. And a farther examination of the flowers of different plants would reveal a surprising variety of plans. Nevertheless, if we com- pare the flower of trillium with that of alily for example, or the flower ot dentaria with that of the bitter-cress (cardamine), we shall at once be struck with the similarity in the plan of the 247 248 MORPHOLOGY. flower, and in the number and arrangement of its members. This suggests to us that there may be some kinship, or rela- tionship between the lily and trillium, and between the bitter- cress and toothwort. Jn fact it is through the interpretation of these different plans that we are able to read in the book of nature of the relationship of these plants. As we found in the case of the ferns that the most important characters of rela- tionship among genera and species are found among the spore- bearing leaves, so here the characters pertaining to the stamens and carpels are the principal guide posts, though the floral en- velopes are only second in importance, and leaves also frequently demand attention. Bearing these facts in mind, we can inquire of the plants themselves about some of the attributes of their families and tribes. NOTE FOR REFERENCE. 482. Arrangement of flowers.—The arrangement of the flowers (inflores- cence) on the stem is important in showing kinships. The flowers may be scattered and distant from each other on the plant, or they may be crowded close together in spikes, catkins, heads, etc. Many of the flower arrangements are dependent on the manner of the branching of the stem. Some of the systems of branching are as follows: 483. I. Dichoromous BRANCHING.—True dichotomy (forking) does not * occur in the shoots of flowering plants, but it does occur in some of the flower clusters. 484. II. LATERAL BRANCHING.—Two main types. Monopodial branching.—This occurs where the main shoot continues to grow more vigorously than the lateral branches which arise in succes- sion around the main stem. Examples in shoots, horse-chestnut, pines (see chapter on pine). Examples in flower clusters (from indetermi- nate inflorescence). Raceme; \ateral axes unbranched, youngest flowers near the terminal portion of long main axis; ex. choke-cherry, currant, etc. Spike; main axis long, lateral unbranched axes with sessile and often crowded flowers; ¢x. pliuntain. Where the main axis is fleshy the spike forms a spadix, as in skunk’s cabbage, Indian turnip, ete.; if the spike falls away aftcr maturity of the flower or fruit it is a cas hin or ament (willows, oaks, etc.). LESSONS ON PLANT FAMILIES. 249 Umbel; the main axis is shortened, and the stalked flowers appear to form terminal clusters or whorls, as in the parsley, carrot, parsnip, etc. flead, or capitulum,; the main axis is shortened and broadened, and bears sessile flowers, as in the sunflower, button-bush, etc. Panicle; when the. raceme has the lateral axes branched it forms a panicle, as in the oat. When the panicle is flattened it forms a corymb. Sympodial branching or cymose branching.—The branches, or lateral axes, grow more vigorously than the main axis, and form for the time false axes (form cymes). 4. Monochasium, only one lateral branch is produced from each rela- tive or false axis. Helicoid cyme,; when the successive lateral branches always arise on the same side of the false axis, as in flower clusters of the forget- me-not. Scorpioid cyme,; when the lateral branches arise alternately on op- posite sides of the false axis. 2. Dichasium, each relative, or false, axis produces two branches» often forming a false dichotomy. Examples in shoots are found in the lilac, where the shoot appears to have a dichotomous branch- ing, though it is a false dichotomy. Forking cyme, flower cluster of chickweed. 3. Pleiochasium, each relative, or false, axis produces more than two branches. 485. The fruit.—The fruit of the angiosperms varies greatly, and often is greatly complicated. When the gyncecium is apocarpous (that is when the carpels are from the first @/s¢inc¢t) the ripe carpels are separate, and each is a fruit. In the syxcarpous gynecium (when the carpels are united) the fruit is more complicated, and still more so when other parts of the flower than the gynoecium remain united with it in the fruit. Pericarp, this is the part of the fruit which envelops the seed, and may consist of the carpels alone, or of the carpels and the adherent part of the receptacle, or calyx; it forms the wall of the fruit. LEndocarp and exocarp. If the pericarp shows two different layers, or zones, of tissue, the outer is the exocarp, and the inner the endocarp, as in the cherry, peach, etc. Mesocarp; where there is an intermediate zone it is the mesocarp. I. CAPSULE (dry fruits). The capsule has a dry pericarp which opens (dehisces) at maturity. When the capsule is syzcarpous the carpels may separate along the line of their union with each other longitudinally (septicidal dehiscence); or each carpel may split down the middle line 250 MORPHOLOGY. (loculicidal dehiscence) as in fruit of iris; or the carpels may open by pores (porictdal dehiscence), as in the poppy. Follicle; a capsule with a single carpel which dehisces along the ventral, or upper, suture (darkspur, peony). Legume or pod; a capsule with a single carpel which dehisces along both sutures (pea, bean, etc.). Silique; a capsule of two carpels, which separate at maturity, leaving the partition wall persistent (toothwort, shepherd’s-purse, and most others of the mustard family); when short it is a silicle or pouch. Pyxidium or pyxis, the capsule opens with a lid (plantain). II. DRY INDEHISCENT FRUITS; do not dehisce or separate into distinct carpels. Nuts; with a dry, hard pericarp. Caryopsis; with one seed and a dry leathery pericarp (grasses). Achene; with pericarp adherent to the seed (sunflower and other com- posites. III. Scuizocarp; a dry, several-loculed fruit, in which the carpels separate from each other at maturity but do not dehisce (umbelliferze, mallow). IV. Berry; endocarp and mesocarp both juicy (grape). V. Pome; mesocarp and outer portion of endocarp soft and juicy, inner portion of endocarp papery (apple). VI. DRUPE, OR STONE FRUIT; endocarp hard and stony, exocarp soft and generally juicy (cherry, walnut); in the cocoanut the exocarp is soft and spongy. CHAPTER NNXVII. MONOCOTYLEDONS. Topic I: Monocotyledons with conspicuous petals (Petaloidez). Lesson I. Lity Fairy (LILIACE#). CLASSIFICATION. 486. Species.—It is not necessary for one to be a botanist in order to recognize, during a stroll in the woods where the tril- lium is flowering, that there are many individual plants very like each other. They may vary in size, and the parts may differ a little in form. When the flowers first open they are usually white, and in age they generally become pinkish. In some in- dividuals they are pinkish when they first open. Even with these variations, which are trifling in comparison with SS the points of close agreement, we recog- nize the individuals to be of the same kind, just as we recognize the corn plants grown jj from the seed of an ear of -~ Fig. 324. . t Trillium — erec- corn as of the same kind. a tum (purple form), arse e two plants from Individuals of the same one root-stock. kind, in this sense, form a sfeczes. The white wake-robin, then, is a species, +2 van m 252 MONOCOTYLEDONS. But there are other trilliums which differ greatly from this one. The purple trillium (T. erectum) shown in fig. 324 is very dif- ferent from it. So are a number of others. But the purple trillium is a species. It is made up of individuals variable, yet very like one another, more so than any one of them is like the white wake-robin. 487. Genus.—Yet if we study all parts of the plant, the per- ennial root stock, the annual shoot, and the parts of the flower, we find a great resemblance. In this respect we find that there are several species which possess the same general characters. In other words, there is a relationship between these different species, a relationship which includes more than the individuals of one kind. It includes several kinds. Obviously, then, this is a relationship with broader limits, and of a higher grade, than that of the individuals of a species. The grade next higher than species we call gezuws. Trillium, then, isa genus. Briefly the characters of the genus trillium are as follows. 488. Genus trillium.—Perianth of six parts: sepals 3, her- baceous, persistent ; petals colored. Stamens 6 (in two whorls), anthers opening inward. Ovary 3-loculed, 3-6-angled ; stig- mas 3, slender, spreading. Herbs with a stout perennial root- stock with fleshy scale-like leaves, from which the low annual shoot arises bearing a terminal flower, and 3 large netted-veined leaves in a whorl. Note.—In speaking of the genus the present usage is to say trillium, but two words are usually employed in speaking of the species, as ‘Trillium grandiflorum, T. erectum, ete. 489. Genus erythronium.— The yellow adder-tongue, or dog-tooth violet (Erythronium americanum), shown in fig. 325, is quite different from any species of trillium. — It differs more from any of the species of trilium than they do from each other. The perianth is of six parts, light ycllow, often spotted near the base. Stamens are 6. The ovary is obovate, tapering at the base, 3-valved, seeds rather numerous, and the style is elongated. The flower stem, or scape, arises from a scaly bulb deep in the soil, and is sheathed by two elliptical-lanceolate, mottled leaves, PLANT FAMILIES: LILIACE-. 25 3 The smaller plants have no flower and but one leaf, while the bulb is nearer the surface. Each year new bulbs are form- ed at the end of run- ners from a parent__ bulb. These run- KS ners penetrate each WW year deeper in the soil. The deeper bulbs bear the flow- er stems. 490. Genus lili- um.—While the lily differs from either the trillium or ery- thronium, yet we recognize a_ rela- tionship when we compare the peri- , Ny i Wy Zify anth of six colored Ce parts, the 6 stamens, =e and the 3-sided and Fig. 325. Adder-tongue (erythronium). At left below pistil, and three lon is a5) loculed stamens opposite three parts of the perianth. Bulb at the right. ovary. 491. Family liliacee.—The relationship between genera, as between trillium, erythronium, and liium, brings us to a still higher order of relationship where the limits are broader than in the genus. Genera which are thus related make up the family. In the case of these genera the family has been named after the lily, and is the lily family, or Zitacee. This grouping of plants into species, genera, families, etc., according to characters and relationships is c/assefication, or davonomy. The lily family isa large one. Another example is found in the ‘‘ Solomon’s-seal,’’ with its elongated, perennial root-stock, the scars formed by the falling away of each annual shoot resem- 254 MONOCOTYLEDONS. bling a seal. The onion, smilax, asparagus, lily of the valley, etc., are members of the lily family. The parts of the flower are usually in threes, though there is an exception in the genus Onifolium, where the parts are in twos. A remarkable excep- tion occurs sometimes in Trillium grandiflorum, where the flower is abnormal and the parts are in twos. 492. Floral formula.—A formula is sometimes written to show at a glance the general points of agreement in the flower among the members of a family or group. The floral formula of the lily family is written as follows : Calyx 3, Corolla 3, Andrceecium 6(3-3), Gyncecium 3. The formula may be abbreviated thus : Ca3,Co3,A6(3-3),G3. 493. Adhesion and cohesion.—In the lily family all the sets, or whorls of parts, are free ; that is, no floral set is adherent to another. Farther, the parts of the calyx, corolla, and andreecium are ds/inct. But the parts of the gyncecium are coherent, i.e. the three carpels are united into a single com- pound pistil. In the floral formula this cohesion of the parts of a set is represented by a small bracket over the figure, as in the gyncecium of the lily family. 494. Floral diagram.—The relation of the parts of the flower on the axis is often represented by a diagram, as shown in fig. 326 for the water-plantain family. 495. Note.—In the following lessons on plant families practical exercises may be conducted, employing representative plants in the several important families. Sketches should be made of the form of the leaves, their relation to the stem; stipules; parts of the flower, and other salient and important characters. Floral formulas and diagrams may be made. Brief notes and descriptions, made from the specimens them- selves and not from the books, should be appended. The plants chosen here need not be insisted upon, for Fig. 326. others equally good may be found. The studies Diagram of alisma presented are offered as suggestions to indicate the flower. (Vines.) 2 E - 9 way in which relationships may be detected, and a familiarity with the characters of the families may be obtained. Several of these lessons are chosen among the monocotyledons, to which the lily family also belongs. 496. Water-plantain family (alismacee).—If we wish to begin with a more simple and primitive family, the water-plantain family will serve the purpose. The common water plantain (Alisma plantago) is an example. It occurs in ditches and muddy shores of streams and lakes. The flowers are in a loose panicle and are inconspicuous. The leaves resemble those of the PLANT FAMILIES: ORCHIDACE. 255 plantain, hence the common name of water-plantain. The flower is regular (all parts of a set are alike), and all the parts are distinct and free. This represents a simpler and more primitive condition than exists in the lily family, where the carpels are united. The floral formula is as follows: Ca3,Co3,A6,G6 — 20 ; i.e. the parts are in threes or multiples of three. The stamens are in pairs in front of the sepals, and really represent but three sta- mens, since it is believed each one has divided, thus making three pairs. No stamens stand in front of the petals in the water plantain, but in the European genus Butomus one stamen in addition stands in front of each sepal. 497. The arrow leaf (genus sagittaria) occurs in wet ground, or on the margins of streamsand ponds. The leaves are very variable, and this seems to depend to some extent on the depth of the water. Several forms of this plant are shown in figs. 493-495. The flowers are moncecious or dicecious. 498. The orchid family (orchidacee).—Among the orchids are found the most striking departures from the arrangement of the flower which we found in the simpler monocoty- ledons. An example of this is seen in the lady- slipper (cypripedium, shown in fig. 464). The ovary appears to be below the calyx and corolla. This is brought about by the adhesion of the lower part of the calyx to the wall of the ovary. The ovary then is inferior, while the calyx and corolla are epigynous. The stamens are united with the style Fig. 327. Flower of an orchid (epipactis), the inferior ovary by adhesion, two lateral twisted as in all orchids so as to bring the upper part of 3 the flower below. perfect ones and one upper imperfect one. The stamens are thus gynandrous. The sepals and petals are each three in number. One of the petals, the ‘‘slipper,”’ is large, nearly horizontal, and forms the “lip” or ‘labellum ” of the orchid flower. The labellum is the platform or landing place for the insect in cross polli- nation (see Part III, Pollination). Above the labellum stands one of the sepals more showy than the others, the ‘banner.’ The two lateral “¢strings ” of the slipper are the two other petals. The stamens are still more reduced in some other genera, while in several tropical orchids three normal stamens are present. 499. There are thus four striking modifications of the orchid flower: Ist, 256 MONOCOTYLEDONS. the flower is irregular (the parts ofa set are different in size and shape); 2d, adnation of all parts with the pistil; 3d, reduction and suppression of the stamens; 4th, the ovary is twisted half way around so that the posterior side of the flower becomes anterior. Floral diagrams in fig. 328 show the posi- Fig. 329. Diagrams of orchid flowers. A, the usual Diagram of flower type; 2, of cypripedium. (Vines.) of canna. tion of the stamens in two distinct types. The number of orchid species is very large, and the majority are found in tropical countries. 500. Related to the orchids are the iris family, in which the stigma is ex- panded into the form of a petal, and the canna family. In the canna the flower is irregular (see figs. 467, 468) and the ovary is inferior. (See chap- ter on pollination, Part III, for description of the canna flower.) CHAPTER XXXVIII. MONOCOTYLEDONS CONCLUDED. Topic Il: Monocotyledons with flowers on a spadix (Spadicifloree). 501. Lesson II. The arum family (araceew).—This family is well represented by several plants. The skunk’s cabbage (Spathyema feetida) illustrated in figs. 455-457 is an interest- ing example. The flowers are closely crowded around a thick stem axis. Such an arrangement of flowers forms a ‘‘ spadix.”’ The spadix is partly enclosed in a large bract, the ‘‘ spathe.”’ The sepals and stamens are four in number, and the pistil has a four-angled style. The corolla is wanting. (See chapter on pollination, Part III, for farther characters of the flower. ) 502. The ‘ jack-in-the-pulpit,’’ also called ‘‘ Indian turnip ’’ (Ariszema triphyllum), shown in fig. 458, the water arum (Calla palustris), and the sweet flag (Acorus calamus) are members of this family, as also are the callas and caladiums grown in con- servatories. The parts of several of the species of this family, especially the corm of the Indian turnip, are very acrid to the taste. The floral parts are more or less reduced. 508. Related to the arum family are the ‘‘duckweeds.’’ Among the members of this family are the most diminutive of the flowering plants, as well as the most reduced floral structures. (For description and illustration of three of these duckweeds, see chapter on nutrition in Part III.) Other related families are the cat-tails and palms. In the latter the spathe and spadix are of enormous size. The cocoa- nut is the fruit of the cocoanut palm. 257 258 MONOCOTYLEDONS. Topic III: Monocotyledons with a glume subtending the flower (Glumiflore). 504. Lesson ITI. Grass family (graminee). Oat.—As a representative of the grass family (graminez) one may take the oat plant, which is widely cultivated, and also can be grown readily in gardens, or perhaps in small quantities in greenhouses in order to have material in a fresh condition for study. Or we may have recourse to material preserved in alcohol for the dis- o® Ged a Fig. 334. i . 3 < Flower of Fig. 330. Fig. 331. Fig. 332. Fig. 333. oat, caw Spikelet — of One glume re- Flower opened Section show- ingthe upper oat showing moved showing showing two palets, ing ground plan palet behind, two glumes. fertile flower. three stamens, and _ of flower. a,axis. and the two two lodicules at base lodicules in of pistil. front. section of the flower. The plants grow usually in stools; the stem is cylindrical, and marked by distinct nodes as in the corn plant. The leaves possess a sheath and blade. ‘The flowers form a loose head of a type known as a panicle. Each little cluster as shown in figure 330 is a spikelet, and consists usu- ally here of one or two fertile flowers below and one or two undeveloped flowers above. We see that there are several series of overlapping scales. The two lower ones are “« glumes,’’ PLANT FAMILIES: GRAMINE. 259 and because they bear no flower in their axils are empty glumes. Within these empty glumes and a little higher on the axis of the spike is seen a boat-shaped body, formed of a scale, the margins of which are folded around the flowers within, and the edges inrolled in a peculiar manner when mature. From the back of this glume is borne usually an awn. If we carefully remove this scale, the ‘‘ flower glume,’’ we find that there is another scale on the opposite (inner) side, and much smaller. This is the ‘ palet.”’ 505. Next above this we have the flower, and the most prom- inent part of the flower, as we see, is the short pistil with the two plume-like styles, and the three stamens at fig. 332. But if we are careful in the dissection of the parts we shall see, on looking close below the pistil on the side of the flowering glume, that there are two minute scales (fig. 334). These are what are termed the dodicules, considered by some to be merely bracts, \\ by others to representa pe- --.\Q rianth, that is two of the sepals, the third sepal hav- ing entirely aborted. Ru- diments of this third sepal Fig. 335. : Diagram of oat spikelet. G/, glumes; BZ, palets; are present in some of the 4, abortive flower. : R graminee. 506. To the gramineze belong also the wheat, barley, corn, the grasses, etc. The graminez, while belonging to the class monocotyledons, are less closely allied to the other families of the class than these families are to each other. For this reason they are regarded as a very natural group. 507. The sedge family (cyperacez). Carex.—As a representative of the sedges a species of the genus carex may be studied. If plants of Carex lupulina are taken from the soil carefully we find that there is an under- 260 MONOCOTYLEDONS. ground stem or root-stock which each year grows a few inches, forms new attachments by roots to the soil, and thus the plant may spread from year to year. This underground stem, as seen, has only scaly leaves. The upright stems reach a height of two to three feet, and are prominently three-angled, as are most of the species of this large genus. The leaves are three-ranked, and consist of a long sheathing base and a long narrow blade. The flowers, as we see, are clustered at the end of the stem, or sometimes additional ones arise in the axils of the - leaves lower down on the stem. The staminate flowers form a slender, short spike, terminat- ing the stem, while the pistil- late flowers form several spikes arising as branches. Fig. 336. _ Flowers of Carex lupulina; staminate flower spike above, three pistillate flower spikes below. Details of pistillate and staminate flowers shown at the right. The flowers are very much reduced here, and each of the pistillate flowers consists of one pistil which is surrounded by a flask-shaped scale, the per/- gynium. These perigynia can be distinctly seen upon the spike. At the apex of the perigynia the three styles emerge. Just below cach perigynium PLANT FAMILIES: CYPERACE. 261 is a slender scale, the primary bract, from the axil of which the pistillate flower arises. Fig. 337. Fig. 338. Fig. 339. Two carex flowers. Pistil of carex. Section of pistil. For the study of the flowers one must select material at the time the male flowers are in bloom. In fig. 340 is represented a portion of the staminate spike of Carex laniflora. As seen here each staminate flower consists of three stamens. These stamens arise in the axil of a bract. Figure 337 represents a portion of the pistillate spike of the same species at the time of flowering. The fact that the parts, or members, of the flower are in threes suggests that there may be some relationship be- tween the carex and the monoco- tyledons already studied, even though each flower has become sv reduced in the number of its members. 508. In the bulrush (scirpus), another genus of this family, the flowers are perfect and complete Fig. 340 (having all parts of the flower), Two male flowers of Carex laxiflora. with the parts in threes or some multiple of three. Here there is a more obvious resemblance to the monocotyledenous type, CHAPTER XXXIX. DICOTYLEDONS. Topic IV: Dicotyledons with distinct petals, flowers in catkins, or aments; often degenerate. 509. Lesson IV. The willow family (salicacee).—The wil- lows represent a very interesting group of plants in which the Spray of willow leaves, pistillate and staminate catkins (Salix discolor). Ke flowers are greatly reduced. The flowers are crowded on a more or less elongated axis forming a ca/tim, or ament. The ament is characteristic of several other families also. The willows are dicecious, the male and female catkins being borne 262 PLANT FAMILIES: CUPULIFERA. 263 on different plants. The catkins appear like great masses of either stamens or pistils. But if we dissect off several of the flowers from the axis, we find that there are many flowers, each one subtended by a small bract. In the male or ‘‘sterile’’ cat- kins the flower consists of two to eight stamens, while in the female or ‘‘ fertile’’ catkins the flower consists of a single pistil. The poplars and willows make up the willow family. 510. Lesson V. The oak family (cupulifere).—A small branch of the red oak (Quercus rubra) is illustrated in fig. 342. . Fig. 342. Spray of oak leaves and flowers. Below at right is staminate flower, at left pistillate flower. This is one of the rarer oaks, and is difficult for the beginner to distinguish from the scarlet oak. The white oak is perhaps in 264 DICOTYLEDONS. some localities a more convenient species to study. But for the general description here the red oak will serve the purpose. Just as the leaves are expand- ing in the spring, the deli- cate sprays of pendulous male catkins form beauti- ful objects. The petals are wanting in the flower, andthe sepals forma united Branch of the butter- 4 nut. Cluster of female g flowers at the top, show- ing the two styles of each pistil, catkins below. calyx, with several lobes, that is, the parts of the calyx are coherent. In the male flowers the calyx is bell-shaped and deeply lobed. The pendent stamens, variable in number, just reach below its margin. The pistillate or female flowers are not borne in catkins, but stand on short stalks, either singly or a few in a cluster. ‘The calyx here is urn-shaped with short lobes. The ovary consists of three united (coherent) carpels, and there are three stigmas. Only one seed is developed in the ovary, and the fruit is an acorn. The numerous scales at the base of the ovary form a scaly involucre, the cup. 5il. The beech, chestnut, and oak are members of the oak family. 512. The following additional families among the ament bearers are represented in this country: the birch family (birch, alder), the hazelnut family (hazelnut, hornbeam, etc. ), walnut family (hickory, walnut), and the sweet-gale family (myrica). CHAPTER XL. DICOTYLEDONS CONTINUED. Topic V: Dicotyledons with distinct petals and hypogynous flowers. URTICIFLORA. 513. The nettle family (urticacee).—The nettle family receives its name from the members of one genus in which the stinging nettles are found (urtica). The dicecious nettle (U. dioica) has opposite, petioled leaves, which are ovate, with a heart-shaped base. The margins of the leaves are Urtica, diagram of male flower. Fig. 344. The dicecious nettle ( Urtica dioica), showing leaves, flower clusters, and Fig. 346. below staminate flower at the right Urtica, diagram of and pistillate flower at left. female flower. deeply serrate, and the lower surface is downy. The stems and petioles of the leaves are armed with stinging hairs. 514. The greenish flowers are borne in dense clusters in the form of branched racemes which arise from the axils of the leaves. The staminate 265 266 DICOTYLEDONS. flowers have four small sepals and four stamens. The fertile flowers (pistil- late) have also four sepals. The pistil has a two-loculed ovary; one of the locules is the smaller, and later disappears, so that the fruit is a one-seeded achene. The parts of the flower are in twos, since the four sepals are in two pairs. 515. Lesson VI. The elm family (ulmacee).—'The elm tree belongs to this family. The leaves of our American elm (Ulmus americana) are ovate, pointed, deeply serrate, and with an ob- lique base as shown in fig. 347. The narrow stipules which are Fig. 347. Spray of leaves and flowers of the American elm; at the left above is section of flower, next is winged seed (a samara). present when the leaves first come from the bud soon fall away. The flowers are in lateral clusters, which arise from the axils of the leaves, and appear in the spring before the leaves. They hang by long pedicels, and the petals are absent. The calyx is bell-shaped, and 4-9-cleft on the margin. The stamens vary also in number in about the same proportion.