i cers oe ar, a RG ot rans x rete i eis} eet by ats sire ne if é poe Fe = iia) terse reye Peielarsscra: tare, any; Eee sah reth a te FSS rr ereis SI; Yeoh tet aL sire §, Pht r By ets) ia es ers Ue aie7e Sects sc aurea he Te tale (aoa iss Say ca nee: Sad as are eee, ht *e sais a be Cr RE it, Presets ei beet fa ie aah os ne Sac sane fit) Thy a ie iy ; at nou ts ei ‘ ayer spies peaked eeeeecpatht bs 3 eet ere eerste cater ay yah a cars hota oe oes) % Fy irae 89. Neh pera renee ay Ra Cornell University Library Elementary botany Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http:/Awww.archive.org/details/cu31924000422794 (19082 f82 440.67) “(uit adud 39s) VLATOAMN SVD.A.) ELEMENTARY BOTANY BY GEORGE FRANCIS ATKINSON, PuH.B. Professor of Botany in Cornell University THIRD EDITION, REVISED oy ty 7 \1 \ifee 1 cy NEW YORK HENRY HOLT AND COMPANY 1908 Copyright, 1898, 1905 BY HENRY HOLT AND COMPANY ROBERT PRUMMOND COMPANY, PRINTERS, NEW YORK PREFACE. THE present book is the result of a revision and elaboration of the author’s “Elementary Botany,” New York, 1898. The general plan of the parts on physiology and general morphology remains unchanged. A number of the chapters in the physio- logical part are practically untouched, while others are thoroughly revised and considerable new matter is added, especially on the subjects of nutrition and digestion. The principal chapters on general morphology are unchanged or only slightly modified, the greatest change being in a revision of the subject of the morphology of fertilization in the gymnosperms and angiosperms in order to bring this subject abreast of the discoveries of the past few years. One of the greatest modifications has been in the addition of chapters on the classification of the algae and fungi with studies of additional examples for the benefit of those schools where the time allowed for the first year’s course makes desirable the examination of a broader range of representative plants. The classification is also carried out with greater definite- ness, so that the regular sequence of classes, orders, and families is given at the close of each of the subkingdoms. Thus all the classes, all the orders (except a few in the alge), and many of the families, are given for the alge, fungi, mosses, liverworts, pteridophytes, gymnosperms, and angiosperms. But by far the greatest improvement has been in the complete reorganization, rewriting, and elaboration of the part dealing with ecology, which has been made possible by studies of the past few years, so that the subject can be presented in a more logical and coherent form. As a result the subject-matter of ili lv PREFACE. the book falls naturally into three parts, which may be passed in review as follows: Part I. Physiology. This deals with the life processes of plants, as absorption, transpiration, conduction, photosynthesis, nutrition, assimilation, digestion, respiration, growth, and _ irritability. Since protoplasm is fundamental to all the life work of the plant, this subject is dealt with first, and the student is led through the study of, and experimentation with, the simpler as well as some of the higher plants, to a general understanding of protoplasm and the special way in which it enables the plant to carry on its work and to adjust itself to the conditions of its existence. This study also serves the purpose of familiarizing the pupil with some of the lower and unfamiliar plants. Some teachers will prefer to begin the study with general morphology and classification, thus studying first the represen- tatives of the great groups of plants, and others will prefer to dwell first on the ecological aspects of vegetation. This can be done in the use of this book by beginning with Part II or with Part III. But the author believes that morphology can best be com- prehended after a general study of life processes and functions of the different parts of plants, including in this study some of the lower forms of plant life where some of these processes can more readily be observed. The pupil is then prepared for a more intelligent consideration of general and comparative morphology and relationships. Even more important is a first study of physiology before taking up the subject of ecology. The great value to be derived from a study of plants in their relation to environment lies in the ability to interpret the dif- ferent states, conditions, behavior, and associations of the plant, and for this physiology is indispensable. It is true that a con- siderable measure of success can be obtained by a good teacher in beginning with either subject, but the writer believes that measure of success would be greater if the subjects were taken up in the order presented here. Part II. Morphology and lije history of representative plants, PREFACE, Vv This includes a rather careful study of representative examples among the alge, fungi, liverworts, mosses, ferns and_ their allies, gymnosperms and angiosperms, with especial emphasis on the form of plant parts, and a comparison of them in the different groups, with a comparative study of development, reproduction, and fertilization, rounding out the work with a study of life histories and noting progression and retrogression of certain organs and phases in proceeding from the lower to the higher plants. Thus, in the alge a first critical study is made of four examples which illustrate in a marked way progressive stages of the plant body, sexual organs, and reproduction. Addi- tional examples are then studied for the purpose of acquiring a knowledge of variations from these types and to give a broader basis for the brief consideration of general relationships and classification. A similar plan is followed in the other great groups. The processes of fertilization and reproduction can be most easily observed in the lower plants like the alge and fungi, and this is an additional argument in favor of giving emphasis to these forms of plant life as well as the advantage of proceeding logic- ally from simpler to more complex forms. Having also learned some of these plants in our study of physiology, we are following another recognized rule of pedagogy, 1.e., proceeding from known objects to unknown structures and processes. Through the study of the organs of reproduction of the lower plants and by general comparative morphology we have come to an under- standing of the morphology of the parts of the flower, and of the true sexual organs of the seed plants, and no student can hope to properly interpret the significance of the flower, or the sexual organs of the seed plants who neglects a careful study of the general morphology of the lower plants. Part III. Plant members in relation to environment. This part deals with the organization of the plant body as a whole in its relation to environment, the organization of plant tissues with a discussion of the principal tissues and a descriptive synopsis of the same. . This is followed by a complete study from a biological vi PREFACE. standpoint of the different members of the plant, their special function and their special relations to environment. The stem, root, leaf, flower, etc., are carefully examined and their ecological relations pointed out. This together with the study of physiology and representatives in the groups of plants forrns a thorough basis for pure plant ecology, or the special study of vegetation in its relation to environment. There is a study of the factors of environment or ecological factors, which in general are grouped under the physical, climatic, and biotic factors. This is followed by an analysis of vegeta- tion forms and structures, plant formations and societies. Then in order are treated briefly forest societies, prairie societies, desert societies, arctic and alpine societies, aquatic societies, and the special societies of sandy, rocky, and marshy places. Acknowledgments. The author wishes to express his grate- fulness to all those who have given aid in the preparation of this work, or of the earlier editions of Elementary Botany; to his associates, Dr. E. J. Durand, Dr. K. M. Wiegand, and Professor W. W. Rowlee, of the botanical department, and to Professor B. M. Duggar of the University of Missouri, Professor J. C. Arthur of Purdue University, and Professor W. F. Ganong of Smith College, for reading one or more portions of the text; as well as to all those who have contributed illustrations. Illustrations. The large majority of the illustrations are new (or are the same as those used in earlier editions of the author’s Elementary Botany) and were made with special reference to the method of treatment followed in the text. Many of the photographs were made by the author. Others were contributed by Professor Rowlee of Cornell University; Mr. John Gifford of New Jersey; Professor B. M. Duggar, University of Missouri; Professor C. Ik. Bessey, University of Nebraska; Dr. M. B. Howe, New York Botanical Garden; Mr. Gifford Pinchot, Chief of the Bureau of Forestry; Mr. B. T. Galloway, Chief of the Bureau of Plant Industry; Professor ‘Tuomey of Yale University; and Mr. I. TH. Harriman, who through Dr. C. H. Merriam of the National Museum allowed the use of several of his copy- PREFACE. vii righted photographs from Alaska. To those who have con- tributed drawings the author is indebted as follows: to Professor Margaret C. Ferguson, Wellesley College; Professor Bertha Stoneman of Huguenot College, South Africa; Mr. H. Hassel- bring of Chicago; Dr. K. Miyake, formerly of Cornell University and now of Doshisha College, Japan; and Professors Ikeno and Hirase of the Tokio Imperial University. The author is also indebted to Ginn & Co., Boston, for the privilege to use from his ‘‘First Studies of Plant Life” the following figures: 28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103, 422-426, 429, 430, 438-440, 443, 444, 448, 449, 452, 472-475. A few others are acknowledged in the text. CoRNELL UNIVERsITy, April, 1905. TABLE: OF ‘GONTENTS, PART I. PHYSIOLOGY. CHAPTER I. PROTOPLASM, 19: shee/sete esses er sdetaeiorhy aeucaiae ache wield eebate eiaoeters CHAPTER II. ABSORPTION, DIFFUSION, OSMOSE........... isisle peannaaeee ewuie sees CHAPTER III. HOW: PLANTS! OBPAIN (WATERS ck case csidarduiels ne ew nee ea iccewe CHAPTER IV. TRANSPIRATION, OR THE LOSS OF WATER BY PLANTS. ....ceeeeeee CHAPTER V. PaTH OF MOVEMENT OF WATER IN PLANTS. ......eece00 oaateiestets CHAPTER VI. MBemaANIest USES OF WATER. o 4.0 oesask ber edesewew ine’ nendaua ee CHAPTER VII. SrarcH AND SUGAR FORMATION. 2 .c.nccicessn ease eewes meee nce es Ehee Wrases Cancermieds £5.00 vaneen ance bac ews we oeaeR Nem eee ox, Where Starch ais? POrmed 5 24sec esc aveerstnarmnenerndrena eaves serena 6 3. Chlorophyll and the Formation of Starch. ...........0.0000- CHAPTER VIII. STARCH AND SUGAR CONCLUDED; ANALYSIS OF PLANT SUBSTANCE.... c. “Translocation of Starcho< 4. 2.2 wes ccsie ec cuwnsveenesae es 2, Sugar; and Digestion of Starch. . -: sc.caesseereeveeadagu cen 3. Rough Analysis of Plant Substance. ........sssseceecceerees 22 35 48 x TABLE OF CONTENTS. CHAPTER IX. PAGE How PrANts (OBTAIN: THEIR: HOOD; ) Tirsciran tooo area se ew ae Ae 81 i: Sources: of Plant: Moods s ¢ Get va swteedeas eed aaceceate dpe 81 2, Parasites:and Saprophytess. an pit cinwada seis scan aieeoa seas 6 83 3. How Fungi Obtain. their Food... cccescevcrsaaeestaecaases 86 4 PIV COLL Za) nxn ta tahateisu ne eemiestee hoe ule Weer ucnme eee ne eee gI G-- Nitrogen-gatherers. 2 c cicists-< cowuye eaemors ssbaeure aes Wee oer 92 Ou TAGHENS 6.27 eeSccaeacaraat «aah Sous acereucro em alaratwis Siore:dlavatalerstelae simi oe 93 CHAPTER X. How PLANgs: OBTAIN THEIR FOOD; Tie sedc eds aeukelsaes ces angeues 97 Seedlings, 97. Digestion, 107. Assimilation... .........++.44. 109 CHAPTER XI. (RESPIRATION: .ja.gisep ses os504h-ouee ey as oe +25 easel eawme eee es aeons IIo CHAPTER XII. GROWDE ca ba Aik oere siti eet siuctsunncit he sia wire Vet me a eee ee veeee 118 CHAPTER NIII. TRRITABILITY. 4 oie2se sted sasieee.n vine ncn soe wes OE Saige ai he eee es os otras 125 PART II. MORPHOLOGY AND LIFE HISTORY OF REPRESENTATIVE PLANTS. CHAPTER NIV. SPIROCGYRA scsi s sowed wk ean eAuine pine nawem eau ote w melee vepaie gO VAUGHERIAS asic e's ecscisisic bet aan slesteersa w aeeceeearee ss cocvcveccesecs 142 CHAPTER XVI. CEDOGONIUM, . ccc cee ee sete tereenseceeeens see eeeccecececee 147 CHAPTER XVII. COLEOCHAETE. 0:6 e6 ca sneieaec sect sae i bea seesaweces secccescceee 153 CHAPTER XVIII. CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALGH.......... 158 CHAPTER XIX., Funot: Mucor AND SAPROLEGNIA.......+% ii slele giclee ced ev wewelse 177 TABLE OF CONTENTS. xi CHAPTER XX. PAGE Funct ContInuepD (‘‘ Rusts” Uredince)....... ...000005 ROOT 187 CHAPTER XXI. THE: HIGHER RUNGE: se-ceruo2e ah ha ncne digas t-e6 eile asciels ssielee eisiels 195 CHAPTER XXII. CLASSIFICATION OF THE FUNGI.............cceecevces Giblele rele wins. 213 CHAPTER XXIII. LIVERWORTS . (Hepaticss) eas; 282s 4aiteneg isos 4 tisreaasce seed ae ae ea’s 222 Ricela, 222,,.. Marchantia.s..: 4 ses. vee ecu vA vada ewsadeeees es 226 CHAPTER XXIV, LIVER WORTS; CONTINUED si ic). d.c.cueeieraieneinieis ine envious, oo b5dc fale nas Bae 231 Sporogonium of Marchantia. .. 2.1... cece eee e cece eee eeeee 231 Leaf yestemmied Liver wOrisss sakes G ao coma tetas encase es 236 The Horned Liverworts: i144 sccc0 eee vee eee esceteeweee ease 240 Classification: of the Liverwortsis..5 c.s) ee casinmeovewere coos 242 CHAPTER XXV. MOSSES. (MUsGl)s(vaddakatapamema bares ahaa a Beineeero eae sarees 243 Classification: of Mossesi inci natin o hsb oy ccs ei oes ee casein 4 248 CHAPTER XXVI. TERNS ies sree cietara) fe eat ase sciece ayn etaernisteveicie wtiereralayale ace a eieie Seser ser CHAPTER XXVII FERNS CONTINUED. os occ cee ce ceeenetteete rset eeeerces Sewanee sd 262 Gametophyte of Ferns... ..-.-seeeeeee eee e ence eee eeeeecees - 262 Sporophyte. .....0.seeeecee cere eee eeeeeeees Sptevergrass eeecccee 268 CHAPTER XXVIII. DIMORPHISM OF FERNS.......0-0sscccecescssecnccccccsccs secees 273 CHAPTER XXIX. HORSETATESI oe ewe sis cuttme tins hk uenu eae an Ataman eels Sas earone 280 CHAPTER XXX. CLUB-MOSSES........ Sete radia aan eA PV he hls ar aVensve SyovarcroneaUeaeer 284 CHAPTER XXXI. QUILLWORTS (Isoetes).. 66. e eee een t nena een e cnet ee eees 289 xi TABLE OF CONTENTS. CHAPTER XXXII. PAGE COMPARISON OF FERNS AND THEIR RELATIVES. .........0..0e00005 292 Classification, of the Pteridophytes:... 2... s2ccac. aq nedeaio3 bes 205 CHAPTER XXXIII. GYNMOSPURMS! ¢oc5 sere cei aceael aye pean ad aeeab Les soe saieoeoenes 207 CHAPTER XXXIV. BURIBER STUDIES: ON GYMNOSPERMS. 2....006 0 sient oe eee gieaceiere bes BI CHAPTER XXXV. MorpPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA... ... 318 CHAPTER XXXVI. GAMETOPHYTE AND SPOROPHYTE OF ANGIOSPERMS. ... 2.00.00 ee00e 325 CHAPTER XXXVII. MorpHoiocy OF THE NUCLEUS AND SIGNIFICANCE OF GAMETOPHYTE AND SEORORA NIRS <3) ox ue ng Ces QON te Ras Sue Oe PEN OH UO 340 PART TI. PLANT MEMBERS IN RELATION TO ENVIRONMENT. CHAPTER XXXVIII. THE ORGANIZATION OF THE PUANT 0 ccc 5 cece n Heine ae eee geal 349 I.. Organization: of Plant, Mem berss... 1... cs08aes sees sancns 349 Il.. Organization of Plant Tissues... 0... ena ee enw nan 356 CHAPTER NXXIX. ‘THe: DIFFERENT: (EVPES: OR STEMS. cccdceas as ween sn pews s Seu weas 365 I. Erect Stems. sng. 22.24 mne sinned cat Rees pis SEES Saree a fe i 365 Il. Creeping, Climbing, and Floating Stems.................. 309 II. Specialized Shoots and Shoots for Storage of Food. ...... eu 8 IV. Annual Growth and Winter Protection of Shoots and Buds... 3 CHAPTER XL. BORTAGH: ERAVIES fends Gisn kee em Gone e Re B5nh eGR EAS Ta care eR ag 383 I. General Form and Arrangement of Leaves. ............... 383 Il.. Protective Modifications-of Leaves... osc en0c0 204844 eewaews 302 II. Pratestive Positions: a.4 scaucco foes eho deee et edesdeR ees 395 IV. Relationof Leaves'to Light.) eco. c0¢beacees besaee teases 307 We wilse@ailt Patkeninee sate. ce aanereanee 3 Sethe cians huaperaraceenai ah ote ieee . 404 TABLE OF CONTENTS. xiil CHAPTER XLI. PAGE SHE ROOTie cnoenin samen hanwed Ome eiae gale Sake ence eae ane 410 Ty HUM Gti Ons OL ROCs Ac snare ee ceee soe oietotoes ah lea cacioe em eee 410 TigsdC Inds OL RGotse tense secs ken eee ta PA hea 415 CHAPTER XLII. ELE: SP VORAT-6S MOOD cra: smenterons satis meee nO ro Aare 419 She. Parts orth BLOWERS 6 a< s2a)ese aoe tered a ee 419 dG Beeps Sab axe oaray god al Fohsidek asia een aC eR a pe eR mee ak Oped dh Mae RN mart ar 421 III. Arrangement of Flowers, or Mode of Inflorescence........ 426 CHAPTER XLIII POLLINATION! S :hcoardans nawen a sinh senecita ge mete ajavaieweieie score seer 433 CHAPTER XLIV. PEE PROUD Laaskatesaieynarseian di neue Nelda a8 erapheniten eee sle Wee an eea ee 450 Te -Partsof the Pruity..ystnaeea shea acs vine des evar oe Relays 450 IL. Indehiscent- Fruits... asus tavnn gaa xced aon see eeeeesaug oe 451 TTT. Dehiscent Bruits c.scnatvua Seana eed AEM ee nee eee eae 452 Mo sPleshiycand ley saUits:, oi < de eroataarscayer rings seme ietard wraceioalals 454 V... Reinforced,,or Accessory; Fruits: «0 sc sissy sa susie vis wie ee avarsts 455 VIL CFruits:6f Gymnospeninss ta sees teen does ce Seavsaacn ae 45 Wit... “Eruit?? of Pers, Mosses, eto. sc scsncatisveveewed be585 457 CHAPTER XLV. DEED: DISPERSAL, 56.e0. cca tepe seus peina antes tees § disuncars;eeve nsw oinse 458 CHAPTER XLVI. VEGETATION IN RELATION TO ENVIRONMENT .....cecccsssaccccces 464 CHAPTER XLVII. GLASSIFIGATION ‘OF ANGIOSPERMS,, 02 ese. bdccnaGurncleies avcayaaes 487 ELS TORE behav ated aecthana ei menace usuy sce oh aac ea fa a fave nat ora tataicsafey anticre Met) sfohete ene airale 503 PART L PHYSIOLOGY. CHAPTER I. PROTOPLASM.* 1. In the study of plant life and growth, it will be found convenient first to inquire into the nature of the substance which we call the living material of plants. For plant growth, as well as some of the other processes of plant life, are at bottom dependent on this living matter. This living matter is called in general profoplasm. 2. In most cases protoplasm cannot be seen without the help of a microscope, and it will be necessary for us here to em- ploy one if we wish to see protoplasm, and to satisfy ourselves by examination that the substance we are dealing with zs protoplasm. 3. We shall find it convenient first to examine protoplasm in some of the simpler plants ; plants which from their minute size and simple structure are so transparent that when examined with the microscope the interior can be seen. For our first study let us take a plant known as spirogyra, though there are a number of others which would serve the pur- pose quite as well, and may quite as easily be obtained for study. 2 PHYSIOLOGY. Protoplasm in spirogyra. 4. The plant spirogyra.—This plant is found in the water of pools, ditches, ponds, or in streams of slow-running water. It is green in color, and occurs in loose mats, usually floating near the surface. The name ‘“‘ pond-scum’’ is sometimes given to this plant, along with others which are more or less closely related. It is an a/ga, and belongs to a group of plants known as alg@. If we lift a portion of it from the water, we see that the mat is made up of a great tangle of green silky threads. Each one of these threads is a plant, so that the number con- tained in one of these floating mats is very great. Let us place a bit of this thread tangle on a glass slip, and examine with the microscope and we will see certain things about the plant which are peculiar to it, and which enable us to dis- tinguish it from other minute green water plants. We shall also wish to learn what these peculiar parts of the plant are, in order to demonstrate the protoplasm in the plant.* 5. Chlorophyll bands in spirogyra.—We first observe the presence of bands; green in color, the edges of which are usually very irregularly notched. These bands course along in a spiral manner near the surface of the thread. There may be one or several of these spirals, according to the species which we happen to select for study. This green coloring matter of the band is chlorophyll, and this substance, which also occurs in the higher green plants, will be considered in a later chapter. At quite regular intervals in the chlorophyll band are small starch grains, grouped in a rounded mass enclosing a minute body, the pyrenoid, which is peculiar to many alge. 6. The spirogyra thread consists of cylindrical cells end to end.—Another thing which attracts our attention, as we examine a thread of spirogyra under the microscope, is that the thread is * Tf spirogyra is forming fruit some of the threads will be lying parallel in pairs, and connected with short tubes. In some of the cells there will be found rounded or oval bodies known as zygospores. These may be seen in fig. 86, and will be described in another part of the book. PROTOPLASM. 3 made up of cylindrical segments or compartments placed end to end. tween the ends. We can see a distinct separating line be- Hach one of these segments or compartments of the thread is a ced/, and the boundary wall is inthe form of a cylinder with closed ends. 7. Protoplasm.—Having distinguished these parts of the plant we can look for the protoplasm. It occurs within the cells. It is colorless (i.e., hyaline) and consequently requires close observa- tion. Near the center of the cell can be seen a rather dense granular body of an elliptical or irregular form, with its long diameter transverse to the axis of the cell in some species; or trian- gular, or quadrate in others. This is the zucleus. Around the nucleus is a granular layer from which delicate threads of a shiny granular substance radiate in a starlike manner, and terminate in the A granular layer of the same substance lines the inside of the cell wall, and can be seen through This chlorophyll band at one of the pyrenoids. the microscope if it is properly focussed. granular substance in the cell is procoplasm. 8. Cell-sap in spirogyra.—The greater part of the interior space of the cell, that between the radiating strands of protoplasm, is occupied by a watery fluid, the ‘‘ cell-sap.’’ 9. Reaction of protoplasm to certain reagents. —We can employ certain tests to demonstrate that this granular substance which we have seen is protoplasm, for it has been found, by repeated experiments with a great many kinds of plants, that protoplasm gives a definite reaction in re- sponse to treatment with certain substances called reagents. Let us mount a few threads of the Thread of spiro- gyra, showing long cells, chlorophyll band, nucieus, strands of proto- plasm, and_ the granular wall layer of protoplasm spirogyra in a drop of a solution of iodine, and observe the 4 PHYSIOLOG Y. results with the aid of the microscope. The iodine gives a yellowish-brown color to the protoplasm, and it can be more distinctly seen. The nucleus is also much more prominent since it colors deeply, and we can perceive within the nucleus one small rounded body, sometimes more, the zucleolus. The iodine here kills and stains the protoplasm. The proto- plasm, however, in a living condition will resist for a time some other reagents, as we shall see if we attempt to stain it with a one per cent aqueous solu- tion of a dye known as eos77. Let us mount a few living threads in such a solution of eosin, and after Fig. 2. Fig. 3. a time wash off Cell of spirogyra before treat- Cell of spirogyra after treatment pas ment with iodine. with alcohol and iodine. the stain. The protoplasm remains uncolored. Now let us place these threads for a short time, two or three minutes, in strong alcohol, which kills the protoplasm. Then mount them in the eosin solution. The protoplasm now takes the eosin stain. After the proto- plasm has been killed we note that the nucleus is no longer elliptical or angular in outline, but is rounded. The strands of protoplasm are no longer in tension as they were when alive. 10. Let us now take some fresh living threads and mount them in water. Place a small drop of dilute glycerine on the slip at one side of the cover glass, and with a bit of filter paper at the other side draw out the water. The glycerine will flow under the cover glass and come in contact with the spirogyra threads. Glycerine absorbs water promptly. Being in contact with the threads it draws water out of the cell cavity, thus caus- PROTOPLASM. 5 ing the layer of protoplasm which lines the inside of the cell wall to collapse, and separate from the wall, drawing the chlorophyll band inward toward the center also. The wall layer of proto- plasm can now be more distinctly seen and its gran- ular character ob- served. We have thus employed three tests to demon- strate that this sub- stance with which we are dealing shows the reac- tions which we . Fig. 4. Fig. 5. know by ex = ie ye o by cxpstl Cell of spirogyra before Cells of spirogyra after treatment ence to be given treatment with glycerine. with glycerine. by protoplasm. We therefore conclude that this colorless and partly granular, slimy substance in the spirogyra cell is proto- plasm, and that when we have performed these experiments, and noted carefully the results, we have seen protoplasm. 11, Earlier use of the term protoplasm.—FEarly students of the living matter in the cell considered it to be alike in substance, but differing in density; so the term protoplasm was applied to all of this living matter. The nucleus was looked upon as simply a denser portion of the protoplasm, and the nucleolus as a still denser portion. Now it is believed that the nucleus is a distinct substance, and a permanent organ of the cell, The remaining por- tion of the protoplasm is now usually spoken of as the cytoplasm. In spirogyra then the cytoplasm in each cell consists of a layer which lines the inside of the cell wall, a nuclear layer, which surrounds the nucleus, and radiating strands which connect the nucleus and wall layers, thus suspending the nucleus near the center of the cell. But it seems best in this elementary study to use the term protoplasm in its general sense. 6 PHYSIOLOGY. Protoplasm in mucor. 12. Let us now examine in a similar way another of the simple plants with the special object in view of demonstrating the protoplasm. For this purpose we may take one of the plants belonging to the group of /ung?. These plants possess no chlorophyll, One of several species of mucor, a common mould, is readily obtainable, and very suitable for this study.* 13. Mycelium of mucor.—A few days after sowing in some gelatinous culture medium we find slender, hyaline threads, which are very much branched, and, radiating from a central point, form circular colonies, if the plant has not been too thickly sown, as shown in fig. 6. These threads of the fungus form the szce- fium. From these characters of the plant, which we can readily see without the aid of a microscope, we note how different it is from spirogyra. To examine for protoplasm let us lift carefully a thin block of gelatine containing the mucor threads, and mount it in water on a glass slip. Under the microscope we see only a small portion of the branched threads. In addition to the absence of chlo- rophyll, which we have already noted, we see that the myce- lium is not divided at short intervals into cells, but appears like a delicate tube with branches, which become successively smaller toward the ends. 14. Appearance of the protoplasm.—Within the tube-like thread now note the protoplasm. It has the same general ap- pearance as that which we noted in spirogyra. It is slimy, or semi-fluid, partly hyaline, and partly granular, the granules con- sisting of minute particles (the mcrosomes). While in mucor the protoplasm has the same general appearance as in spirogyra, its arrangement is very different. In the first place it is plainly * The most suitable preparations of mucor for study are made by growing the plant in a nutrient substance which largely consists of gelatine, or, better, agar-agar, a gelatinous preparation of certain seaweeds. This, after the plant is sown in it, should be poured into sterilized shallow glass plates, called Petrie dishes, PROTOPLASM. 7 continuous throughout the tube. We do not see the prominent radiations of strands around a large nucleus, but still the proto- Fig 6. Colonies of mucor. plasm does not fill the interior of the threads. Here and there are rounded clear spaces termed vacuoles, which are filled with the watery fluid, cell-sap. The nuclei in mucor are very mi- nute, and cannot be seen except after careful treatment with special reagents. 15 Movement of the protoplasm in mucor.—While exam- ining the protoplasm in mucor we are likely to note streaming movements. Often a current is seen flowing slowly down one side of the thread, and another flowing back on the other side, or it may all stream along in the same direction. 16. Test for protoplasm.— Now let us treat the threads with a solution of iodine. ‘The yellowish-brown color appears which is characteristic of protoplasm when subject to this reagent. 8 PHYSIOLOGY. If we attempt to stain the living protoplasm with a one per cent aqueous solution of eosin it resists it for a time, but if we first kill the protoplasm with strong alcohol, it reacts quickly to the application of the eosin. If we treat the living threads with glycerine the protoplasm is contracted away from the wall, as we found to be the case with spirogyra. While the color, Fig. 7. Thread of mucor, showing protoplasm and vacuoles. form and structure of the plant mucor is different from spiro. gyra, and the arrangement of the protoplasm within the plant is also quite different, the reactions when treated by certain re- agents are the same. We are justified then in concluding that the two plants possess in common a substance which we call protoplasm. Protoplasm in nitella. 17. One of the most interesting plants for the study of one remarkable peculiarity of protoplasm is Avz/ed/a. This plant belongs to a small group known as stoneworts. They possess chlorophyll, and, while they are still quite simple as compared with the higher plants, they are much higher in the scale than spirogyra or mucor. ; 18. Form of nitella —A common species of nitella is Av/ella flexilis. It grows in quiet pools of water, The plant consists of a main axis: in the form of a cylinder. At quite regular intervals are whorls of several smaller thread-like outgrowths, which, because of their position, are termed ‘ leaves,”’ though they are not true leaves. These are branched in a characteristic fash- ion at the tip. The main axis also branches, these branches arising in the axil of a whorl, usually singly. The portions of the axis where the whorls arise are the wodes. Each node is made up of a number of small cells definitely arranged. ‘The portion of the axis between two adjacent whorls is an inter- PROTOPLASM. 9 node. These internodes are peculiar. They consist of but a single “cell,” and are cylindrical, with closed ends. They are sometimes 5-10 cm. long. 19. Internode of nitella.—For the study of an internode of nitella, a small one, near the end, or the ends of one of the ‘‘ leaves’’ is best suited, since it is more transparent. A small portion of the plant should be placed SS \ on the glass slip in water with the sa cover glass over a tuft of the branches SS WV near the growing end. Examined with emg \ ra the microscope the green chlorophyll bodies, which \ \i/ form oval or oblong discs, are seen to be very numer- ; \\ \| 3 ous. They lie quite closely side by side and form in B. | perfect rows along the inner surface of the wall. One peculiar feature of the arrangement of the chlorophyll | f bodies is that there are two lines, extending from one J end of the internode to the other on opposite sides, where the chlorophyll bodies are wanting. ‘These are \ 1) known as neutral lines. They run parallel with the 1 y axis of the internode, or in a more or less spiral manner as shown in fig. 9. 20. Cyclosis in nitella.—The chlorophyll bodies WN 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 f side of the neutral line, we see that the movement is Fig. 8. in the opposite direction. If we examine this move- : : Portion of plant nitella. 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 an uninterrupted rotation, or cyclos’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- plasm 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. fe) 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- Riess, 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 this section we notice that the cells are 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 always lie at the middle of the cell, but often is near one side. If we now apply an alcohol solution of iodine the characteristic yellowish-brown color appears. So we conclude here also that this substance is identical with the living matter in the other very different 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. See note at close of this chapter. 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 Aye SES ay ee ss pra e 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 difh- 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 PHY SIOLOG ¥Y. 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-fuid, 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, Note. In some plants, like elodea for example, it has been found that the streaming of the protoplasm is often induced by some injury or stimu- lus, while in the normal condition the protoplasm docs not move. CHAPTER II. 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 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 zzward 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. Spirogyra from salt solution into water. Fig. a. Spirogyra before placing in salt solu- . tion. Spirogyra in 5% salt solution. Fig. 12. 31. 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. ure from within Fig. 15. After treatment with salt solution. upon the proto- plasmic mem- 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. fully shown in the case of threads Sa a which are recently broken. The cell wall is therefore elastic; 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 surges 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 hmp, and readily bend by pres- Fig. 17. Fig. 18 Fig. 19 Before treatment with salt After treatment with salt From salt solution 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. Bisco: Rigid condition of fresh beet Limp condition after lying in Rigid again after lying ag section. salt solution. ‘ y iniabere: foe oe Figs. 20-22.—Turgor and osmosis in slices of beet withdraws some of the water fram the cell-sap, the cells thus losing their turgidity and the tissues becoming limp or flaccid from the loss of water. ABSORPTION, DIFFUSION, OSMOSE. 7. 83. 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. 84. 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. 13 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. 35. 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 does not escape, or if it does it escapes slowly and after a consider- able time. 86. The coloring matter escapes from dead protoplasm.—lIf, 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. [ere 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 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 plasmolysis 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 apt to be the case by the strong diffusion current and the consequent Root hair of corn strong pressure from Fig. 26. before and after Seedling of mak showing root treatment with 5% without. The membrane pear arta ae 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 goot 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. An artificial cell to illustrate turgor.—Fill a small wide-mouthed vial with a very strong sugar solution. Over the mouth tie firmly a piece of bladder membrane. Be certain that as the membrane is tied over the open end of the vial, the sugar solution fills it in order to keep out air- Fic. 28. Puncturing a make-believe cell after it has been lying in water. Fic. 290. Same as Fig. after needle is removed. bubbles. Sink the vial in a vessel of fresh water and leave it there for twenty- four hours. Remove the vial and note that the membrane is arched out- ward. Thrust a sharp needle through the membrane when it is arched outward, and quickly pull it out. The liquid spurts out because of the inside pressure. 42. 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 ABSORPTION, DIFFUSION, OSMOSE. 21 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. 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 difh- 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 ificreased, 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 osmosts. 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 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. HOW PLANTS OBTAIN WATER. In connection with the study of the means of absorption from the soil or water by 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, cedogonium, and vau- cheria; expanded masses of cells as are found in the thalloid 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 farther in the higher land plants. 45. Absorption by Algz and Fungi.—In the simpler forms of plant life, as in spirogyra and many of the alge and fungi, the plant body is not dif- ferentiated into parts.* In many other cases the only differentiation is between the growing part and the fruiting part. In the alge 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 flat- tened, as in the sea-wrack, or ulva, it is a frond. The Latin word for frond is thallus, and this name is applied to the plant body of all the lower plants, the alge and fungi. The alge and fungi together are sometimes called the thallophytes, or thallus plants. The word thallus is also some- times applied to the flattened body of the liverworts. In the foliose liver- worts 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. In nearly all of the algz the plant body is submerged in water. In these * See Chapter 38 for organization of members of the plant body. 22 HOW PLANTS OBTAIN WATER. 23 cases absorption takes place through all portions of the surface in contact with the water, as in spirogyra, vaucheria, and all of the larger seaweeds. Comparatively few of the alge grow on the surfaces of rocks or trees. In these examples it is likely that at times only portions of the plant body serve in the process of absorption of water from the substratum. A few of the alge are parasitic, living in the tissues of higher plants, where they are surrounded by the water or liquids within the host. Absorption takes place in the same way in many of the fungi. The aquatic fungi are im- mersed in water. In other forms, like mucor, a portion of the mycelium is within the substratum, and being bathed by the water or watery solu- tions absorbs the same, while the fruiting portion and the aerial mycelium obtain their water and food solutions from the mycelium in the substratum. In higher fungi, like the mushrooms, the mycelium within the ground or decaying wood absorbs the water necessary for the fruiting portion; while in the case of the parasitic fungi the mycelium lies in the water or liquid within the host. 46. Absorption by liverworts.—In many of the plants termed liverworts the vegetative part of the plant is a thin, flattened, more or less elongated green body know as a thallus. Riccia.—One of these, belonging to the genus riccia, is shown in fig. 30. Its shape is somewhat like that of a minute ribbon which is forked at intervals in a dichot- omous manner, the character- istic 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 pur- pose in the processes of absorp- tion. Another species of riccia Fig. 30. (R. crystallina) is shown in fig. Thallus of Riccia lutescens, 252. This plant is quite circular in outline and occurs on muddy flats. Some species float on the water. 47. Marchantia.—One of the larger and coarser liverworts is figured at 31. This is a very common liverwort, growing in very damp and muddy places and also along the margins of streams, on the mud or upon the surfaces of rocks which are 24 PHYSIOLOGY. bathed with the water. This is known as Marchantia poly- morpha. 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 similar to the root hairs of the seedlings which we have been studying, and they serve the purpose of absorption. Since, how- ever, there are no roots on the marchantia plant, these hair-like 4, fj Fig. 31. Marchantia plant with cupules and gemma; rhizoids below. outgrowths are usually termed here rhizoids. 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 irreg ular 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 curv- ing up over the growing end, thus serving to protect the delicate tissues at the growing point. HOW PLANTS OBTAIN WATER. 25 48. Frullania.—In fig. 32 is shown another liverwort, which ‘ differs greatly in form from the ones we have just been studying in that there is a well-defined axis with lateral leaf-like outgrowths. Such liver- worts 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- - 5 Fig. 34. oi oe Fig. 32. Fig. 33. ner side, = he, is Portion of plant of Portion of same showing forked rhizoids 7 Frullania, a foliose more highly magni- under row of liverwort. fied, showing over- leaves and lobes t hrou g h lapping leaves. of lateral leaves. a which much of the water is absorbed. 49. Absorption by the mosses.—Among the mosses, which are usually common in moist and shaded f 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. 36, we note that it consists of a slender Fig. 35. Foliose liverwort (bazzania) showing dichotomous branching and overlapping leaves. axis with thin flat, green, leaf-like expansions. Examining with 26 PHYSIOLOGY. the microscope the lower end of the axis, which is attached to the substratum, there are seen numerous brown-colored threads more or less branched. 50. Absorption by the higher aquatic plants. the water plants which are entirely submerged in water are the Examples of water-crowfoots, some of the pond- weeds, elodea or water-weeds, the tape- grass, vallisneria, etc. In these plants all parts of the body being submerged, they absorb water with which they are in contact. In other aquatic plants, like the water-lilies, some of the pond- weeds, the duck-meats, etc., are only partially submerged in the water; the upper surface of the leaf or of the leaf- like expansion being exposed to the air, while the under surface lies in close contact with the water, and the stems and the petioles of the leaves are also immersed in water. In these plants absorption takes place through those } parts in contact with the water. 51. Absorption by the duck-meats. —These plants are very curious ex- amples of the higher plants. Lemna.—One of these is illustrated in fig. 37. This is the common duckweed, Lemma trisulca, It is very peculiar in form and in its mode of growth. Each one of the lateral leaf-like expansions extends outwards by the Fig. 36. elongation of the basal part, which becomes Female plant (gametophyte) = Po, of a moss (mnium), showing long and slender. Next, two new lateral ex- thizoids below, and the tuft of leaves above, which protect the archegonia. from near the base, and thus the plant con- pansions are formed on these by prolification tinues to extend. The plant occurs in ponds and ditches and is sometimes very common and abundant. It floats on the surface of the water. While the flattened part of the plant resembles a leaf, it is really the stem, no leaves being present. This expanded green body is usually termed a HOW PLANTS OBTAIN WATER. 27 ‘frond.”” A single rootlet grows out from the under side and is destitute Fig. 37. Fronds of the duckweed (Lemna trisculca). of root hairs. Absorption of water therefore takes place through this rootlet and through the under side of the ‘‘ frond.” 52. Spirodela poly- rhiza.—This is a very curious plant, closely re- lated to the lemna and sometimes placed in the same genus. It occurs in similar situations, and Fig. 38. is very readily grown.in Spirodela polyrhiza. aquaria. It reminds one of a little insect as seen in fig. 38. There are several rootlets on the under side of the frond. Absorption of water takes place here in the same way as in lemna. 53. Absorption in wolffia.—Perhaps the most curious of these modified water plants is the little wolffia, which contains the smallest specimens of the flowering plants. Two species of this genus are shown in figs. 39-41. The plant body is reduced to nothing but a rounded or oval green body, which represents the stem. No leaves or roots are present. The plants multiply by ‘“‘prolification,” the new fronds growing out from a depression on the under side of one end. Absorption takes place through the surface in contact with the water. 54. Absorption by land plants.—Water cultures.—In connec- tion with our inquiry as to how land plants obtain their water, it 28 PHYSIOLOGY. will be convenient to prepare some water cultures to illustrate this and which can also be used later in our study of nutrition (Chapter IX). Fig. 30. Fig. 4o. Fig. 41. Young frond of wolffia Young frond of wolffia Another species ot growing out of older one, separating trom older one. wolffia, the two fronds still connected. 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 deter- mine what ones are necessary constituents of plant food. While the proportion of the mineral elements which enter into the com- position of plant food may vary considerably within certain limits, the concentration of the solutions should not exceed cer- tain limits. A very useful solution is one recommended by Sachs, and is as follows: 55. Formula for water cultures; Wateiiec scar testes trainee te eenaur ee so cee NS 1000 cc. Potassium Mtrale. jacintascies europa entrain sy 0.5 gr. Sodiuni, chlond és: suiesaevenieceswia agama: ous GCaleiimsulpnatenwcotsads ceemaes eee ex oes Oagcs* MacHesitim Sulphate: nies cei caress teeta On Calcium phosphate. . .. um The calcium phosphate is only partly soluble. The solution which is not in use should be kept ina dark cool place to prevent the growth of minute alge. 56. Several different plants are useful for experiments in water cultures, as peas, corn, beans, buckwheat, etc. The sceds of these plants may be germinated, after soaking them for several hours in warm water, by placing HOW PLANTS OBTAIN WATER. 29 them hetween 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 secds should be planted in good soil and kept under the same temperature conditions, for control. When the 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 compari- sons 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. 57. 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 isa 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. 42. cultures they should be wrapped with black Culture cylinder to show position of 2 corn seedling | Hansen). paper or cloth to exclude the light from the liquid, otherwise numerous minute alge are apt to grow and interfere with the experiment. Or the jars may be sunk in pots of earth to serve the same purpose. If crockery jars are used they will not need covering. 58. For some time all the plants grow equally well, until the nutriment stored in the seed is exhausted. The numbers 1, 3 and 4, in soil and nutri- 30 PHYSIOLOGY. 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. 59. 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. 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. 60. How food solutions are carried into the plant. —We can Fig. 43- Section of corn root, showing root hairs formed from elongated epidermal cells. see how water and food solutions are carried into the plant, HOW PLANTS OBTAIN WATER. 31 and we must next turn our attention to the way in which these 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. 43. 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. 61. In the absorption of the watery solutions of plant food by the root 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 solntions along, and would form one of the causes of root pressure, 62. 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 32 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 Fig. 44. 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. 68. 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- Aber. 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. 64. 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 wilting. ‘The soil if examined will appear quite dry te the sense of touch, Let us weigh some of this soil, then dry it by artificial HOW PLANTS OBTAIN WATER. 33 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 with- draw all the moisture from the soil. 65. “ Root pressure” or exudation pressure.—It is a very com- mon thing to note, when certain shrubs or vines are pruned in the spring, the exudation of a watery fluid from the cut surfaces. In the case of the grape vine this has been known to continue for a number of days, and in some cases the amount of liquid, called ‘*sap,’’ which escapes is considerable. In many cases it is directly traceable to the activity of the roots, or root hairs, in ” the absorption of water from the soil. For this reason the term root pressure has been used to denote the force exerted in sup- plying the water from the soil. But there are some who object to the use of this term ‘‘root pressure.’’ The principal objec- tion is that the pressure which brings about the phenomenon known as ‘‘bleeding’’ by plants is not present in the roots alone. This pressure exists under certain conditions in all parts of the plant. The term exudation pressure has been proposed in lieu of root pressure. It should be remembered that the movement of water in the plant is started by the pressure which exists in the root. If the term ‘‘root pressure’’ is used, it should be borne clearly in mind that it does not express the phenomenon exactly in all cases. Root pressure may be measured.—It is possible to measure not only the amount of water which the roots will raise in a given time, but also to measure the force exerted by the roots during root pressure. It has been found that root pressure in the case of the nettle is sufficient to hold a column of water about 4.5 meters (15 ft.) high (Vines), while the root pressure of the vine (Hales, 1721) will hold a column of water about 10 meters (36.5 ft.) high, and the birch (Betula lutea) (Clark, 1873) has a root pressure sufficient to hold a column of water about 25 meters (84.7 ft.) high. 66. Experiment to demonstrate root pressure.—By a very simple method this lifting of water by root pressure is shown. During the summer season 34 PH YVSTOLOG ¥, plants in the open may be used if it is preferred, but plants grown in pots are also very serviceable, and one may use a potted begonia or balsam, the latter being especially useful. The plants are usually convenient to obtain from the greenhouses, to illustrate this phenomenon. The stem is cut off rather close to the soil and a long glass tube is attached to the cut end of the stem, still connected with the roots, by the use of rubber tubing, as shown infigure 45, and a very small quantity of water may be poured in to moisten the cut end of the stem. In a few minutes the water begins to rise in the glass tube. In some cases it rises quite rapidly, so that the column of water can readily be seen to extend higher and higher up in the tube when observed at quite short intervals. (To measure the force of root pressure is rather difficult for elementary work. To measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book for advanced work.) 67. In either case where the experiment is continued for several days it is noticed that the Fig. 45. column of water or of mercury rises and falls at Experiment to 4: : . : show root pressure different times during the same day, that is, the (Detmer). column stands at varying heights; or in other words the root presssure varies during the day. With some plants it has been found that the pressure is greatest at certain times of the day, or at certain seasons of the year. Such variation of root pressure exhibits what is termed a periodicity, and in the case of some plants there is a daily periodicity; while in others there is in addition an annual periodicity. With the grape vine the root pressure is greatest in the forenoon, and decreases from 12-6 p.M., while with the sunflower it is greatest before to A.M., when it begins to decrease. Temperature of the soil is one of the most important external conditions affect- ing the activity of root pressure. CHAPTER IV. TRANSPIRATION, OR THE LOSS OF WATER BY PLANTS. 68. We should now inquire if all the water which is taken up in excess of that which actually suffices for turgidity is used in the elaboration of new materials of construction. We notice when a leaf or shoot is cut away from a plant, unless it is kept in quite a moist condition, or in a damp, cool place, that it becomes flac- cid, and droops. It wilts, as we say. The leaves and shoot lose their turgidity. This fact suggests that there has been a loss of water from the shoot or leaf. It can be readily seen that this loss is not in the form of drops of water which issue from the cut end of the shoot or petiole. What then becomes of the water in the cut leaf or shoot? Fig. 46. To show loss of water from leaves, the leaves just covered. 69. Loss of water from excised leaves.—Let us take a handful of fresh, green, rather succulent leaves, which are free from 35 30 PHYSIOLOGY. water on the surface, and place them under a glass bell jar, which is tightly closed below but which contains no water. Now place this in a brightly lighted window, or in sunlight. In the course of fifteen to thirty minutes we notice that a thin film of moisture is accumulating on the inner surface of the glass jar. After an hour or more the moisture has accumulated so that it appears in the form of small drops of condensed water. We should set up at the same time a bell jar in exactly the same way but which contains no leaves. In this jar there is no condensed moisture on the inner surface. We thus are justified in concluding that Fig. 47. After a few hours drops of water have accumulated on the inside of the jar covering the leaves. the moisture in the former jar comes from the leaves. Since there is no visible water on the surfaces of the leaves, or at the cut ends, before it may have condensed there, we infer that the water escapes from the leaves in the form of water vapor, and that this water vapor, when it comes in contact with the surface of the cold glass, condenses and forms the moisture film, and later the drops of water. The leaves of these cut shoots there- fore lose water in the form of water vapor, and thus a loss of turgidity results. 70. Loss of water from growing plants.—Suppose we now take a small and actively growing plant in a pot, and cover the pot and the soil with a sheet of rubber cloth or flexible oilcloth TRANSPIRATION. 37 which fits tightly around the stem of the plant so that the mois- ture from the soil or from the surface of the pot cannot escape. Then place a bell jar over the plant, and set in a brightly lighted place, at a temperature suitable for growth. In the course of a few minutes on a dry day a moisture film forms on the inner surface of the glass, just as it did in the case of the glass jar con- taining the cut shoots and leaves. Later the moisture has con- densed so that it is in the form of drops. If we have the same leaf surface here as we had with the cut shoots, we shall prob- ably find that a larger amount of water accumulates on the surface of the jar from the plant that is still attached to its roots. 71. Water escapes from the surfaces of living leaves in the form of water vapor.—This living plant then has lost water, which also escapes in the form of water vapor. Since here there are no cut places on the shoots or leaves, we infer that the loss of water vapor takes place from the surfaces of the leaves and from the shoots. It is also to be noted that, while this plant is losing water from the surfaces of the leaves, it does not wilt or lose its turgidity. The roots by their activity and pressure supply water to take the place of that which is given off in the form of water vapor. This loss of water in the form of water vapor by plants is transpiration. 72. A test for the escape of water vapor from plants.—Make a solution of cobalt chloride in water. Saturate several pieces of filter paper with it. Allow them to dry. The water solution of cobalt chloride is red. The paper is also red when it is moist, but when it is thoroughly dry it is blue. It is very sensitive to moisture and the moisture of the air is often sufficient to redden it. Before using dry the paper in an oven or over a flame. 73. Take two bell jars, as shown in fig. 49. Under one place a potted plant, the pot and earth being covered by oiled paper. Or cover the plant with a fruit jar. To a stake in the pot pin a piece of the dried cobalt paper, and at the same time pin to a 38 PHYSIOLOG ¥. stake, in another jar covering no plant, another piece of cobalt paper. They should both be put under the jars at the same time. In a few moments the paper in the jar with the plant will begin to redden. In a short while, ten or fifteen minutes, prob- ably, it will be entirely red, while the paper under the other jar will remain blue, or be only slightly reddened. ‘The water vapor passing off from the living plant comes in contact with the sensi- Fig. 48. Fig. go. Fig. 48.—Water vapor is given off by the leaves when attached to the living plant It condenses into drops of water on the cool surface of the glass covering the plant Fig. 49.—A good way to show that the water passes off from the leaves in the form of water vapor. tive cobalt chloride in the paper and reddens it before there is sufficient vapor present to condense as a film of moisture on the surface of the jar. 74, Experiment to compare loss of water in a dry and a humid atmosphere.—We should now compare the escape of water from the leaves of a plant covered by a bell jar, as in the last experiment, with that which takes place when the plant is TRANSPIRATION. 39 exposed in a normal way in the air of the room or in the open. To do this we should select two plants of the same kind growing in pots, and of approximately the same leafsurface. The potted plants are placed one each on the arms ofa scale. One of the plants is covered in this position with a bell jar. With weights placed on the pan of the other arm the two sides are balanced. In the course of an hour, if the air of the room is dry, moisture has probably accumulated on the inner surface of the glass jar which is used to cover one of the plants. This indicates that there has here been a loss of water. But there is no escape of water vapor into the surrounding air so that the weight on this arm is practically the same as at the beginning of the experiment. We see, however, that the other arm of the balance has risen. We infer that this is the result of the loss of water vapor from the plant onthatarm. Now let us remove the bell jar from the other plant, and with a cloth wipe off all the moisture from the inner surface, and replace the jar over the plant. We note that the end of the scale which holds this plant is still lower than the other end. 75. The loss of water is greater in a dry thanin a humid atmosphere.—This teaches us that while water vapor escaped from the plant under the bell jar, the air in this receiver soon became saturated with the moisture, and thus the farther escape of moisture from the leaves was checked. It also teaches us an- other very important fact, viz., that plants lose water more rapidly through their leaves in a dry air than in a humid or moist atmos- phere. We can now understand why it is that during the very hot and dry part of certain days plants often wilt, while at night- fall, when the atmosphere is more humid, they revive. They lose more water through their leaves during the dry part of the day, other things being equal, than at other times. 76. How transpiration takes place.—Since the water of transpiration passes off in the form of water vapor we are led to inquire if this process is simply evaporation of water through the surface of the leaves, or whether it is controlled to any appreci- able extent by any condition of the living plant. An experiment 40 PHVSIOLOGY. which is instructive in this respect we shall find in a comparison between the transpiration of water from the leaves of a cut shoot, allowed to lie unprotected in a dry room, and a similar cut shoot the leaves of which have been killed. 77. Almost any plant will answer for the experiment. For this purpose I have used the following method. Small branches of the locust (Robinia pseudacacia), of sweet clover (Melilotus alba), and of a heliopsis were selected. One set of the shoots was immersed for a moment in hot water near the boiling point to kill them. The other set was immersed for the same length of time in cold water, so that the surfaces of the leaves might be well wetted, and thus the two sets of leaves at the beginning of the experiment would be similar, so far as the amount of water on their surfaces is con- cerned. All the shoots were then spread out on a table in a dry room, the leaves of the killed shoots being separated where they are inclined to cling together. In a short while all the water has evaporated from the surface of the living leaves, while the leaves of the dead shoots are still wet on the sur- face. In six hours the leaves of the dead shoots from which the surface water had now evaporated were beginning to dry up, while the leaves of the living plants were only becoming flaccid. In twenty-four hours the leaves of the dead shoots were crisp and brittle, while those of the living shoots were only wilted. In twenty-four hours more the leaves of the sweet clover and of the heliopsis were still soft and flexible, showing that they still contained more water than the killed shoots which had been crisp for more than a day. 78. It must be then that during what is termed transpiration the living plant is capable of holding back the water to some extent, which in a dead plant would escape more rapidly by evaporation. It is also known that a body of water with a surface equal to that of a given leaf surface of a plant loses more water by evaporation during the same length of time than the plant loses by transpiration. 79. Structure of a leaf.—We are now led to inquire why it is that a living leaf loses water less rapidly than dead ones, and why less water escapes from a given leaf surface than from an equal surface of water. To understand this it will be necessary to examine the minute structure of a leaf. For this purpose we may select the leaf of an ivy, though many other leaves will answer equally well. From a portion of the leaf we should make very thin cross sections with a razor or other sharp instrument. These sections should be perpendicular to the surface of the leaf TRANSPIRATION. 4I and should be then mounted in water for microscopic examina- tion.* 80. Epidermis of the leaf.—In this section we see that the green part of the leaf is bordered on what are its upper and lower surfaces by a row of cells which : possess no green color. The walls of the cells of each row have nearly par- allel sides, and the cross walls are per- pendicular. These cells form a single layer over both surfaces of the leaf and are termed the ef:dermis. Their walls are quite stout and the outer walls are cuttcularized. 81. Soft tissue of the leaf.—The cells which contain the green chloro- eae: ee? . ZA as Fig. 50. phyll bodies are arranged in two dif. Sechai traich we latches ferent ways. Those on the upper side gommunauon bitwsen sonateand of the leaf are usually long and pris- leaf: stoma closed. matic in form and lhe closely parallel to each other. Because of this arrangement of these cells they are termed the fadzsade cells, and form what is called the palisade layer. The other green cells, lying below, vary greatly in size in different plants and to some extent also in the same plant. Here we notice that they are Fig. 51 : Fig. 52. Stoma open. Stoma closed. elongated, or oval, or Figs. 34, 35-—Section through stomata of ivy leaf. somewhat irregular in form. The most striking peculiarity, however, in their arrange- ment is that they are not usually packed closely together, but each cell touches the other adjacent cells only at certain points. This arrangement of these cells forms quite largespaces between them, the intercellular spaces. If we should examine such a section of a leaf before it is mounted in water we would see that the inter- * Demonstrations may be made with prepared sections of leaves. 42 PHYSIOLOGY. cellular spaces are not filled with water or cell-sap, but are filled with air or some gas. Within the cells, on the other hand, we find the cell-sap and the protoplasm. 82. Stomata.—If we examine carefully the row of epidermal cells on the under surface of the leaf, we find here and there a peculiar arrangement of cells shown at figs. 51,52. This opening Se through the Gre epidermal layer is a stoma. The ~ cells which immediately surround the “~< openings are the guard Fig. 53. = Portion of epidermis of ivy, showing irregular epidermal cells, stoma cells. ‘Ease steer form of the guard cells can be better seen if we tear a leaf in such a way as to strip off a short piece of the lower epidermis, and mount this in water. The guard cells are nearly crescent shaped, and the stoma is elliptical in outline. The epidermal cells are very irregular in outline in this view. We should also note that while the epidermal cells contain no chlorophyll, the guard cells do. 82a. In the ivy leaf the guard cells are quite plain, but in most plants the form as seen in cross-section is irregular in outline, as shown in fig. 53a, which is from a section of a wintergreen leaf. This leaf is interesting because it shows the characteristic struc- ture of leaves of many plants growing in soil where absorption of water by the roots is difficult owing to the cold water, acids, or salts in the water or soil, or in dry soil (see Chapters 47, 54, 55)- The cuticle over the upper epidermis is quite thick. This lessens the loss of water by the leaf. The compact palisades of cells are in two to three cell layers, also reducing the loss of water. 83. The living protoplasm retards the evaporation of water from the leaf.—If we now take into consideration a few facts which we have learned TRANSPIRATION. 43 in a previous chapter, with reference to the physical properties of the living cell, we shall be able to give a partial explanation of the comparative slow- ness with which the water escapes from the leaves. The inner surfaces of the cell walls are lined with the membrane of protoplasm, and within this is the cell-sap. These cells have become turgid by the absorption of the FIO IO Ie Be eas ed0Ger Fig. 53a. Cross-section of leaf of wintergreen. Cu. cuticle; Epid., epidermis; v.d., vascular duct; Jnt.c. sp., intercellular space; L. ep., lower epidermis; St., stoma. water which has passed up to them from the roots. While the protoplas- mic membrane of the cells does not readily permit the water to filter through, yet it is saturated with water, and the elastic cell wall with which it is in contact is also saturated. From the cell wall the water evaporates into the intercellular spaces. But the water is given up slowly through the proto- plasmic membrane, so that the water vapor cannot be given off as rapidly from the cell walls as it could if the protoplasm were dead. The living protoplasmic membrane then which is only slowly permeable to the water of the cell-sap is here a very important factor in checking the too rapid loss of water from the leaves. 44 PH YSIOLOG ¥. By an examination of our leaf section we sce that the intercellular spaces are all connected, and that the stomata, where they occur, open also inte intercellular spaces. There is here an opportunity for the water vapor in the intercellular spaces to escape when the stomata are open 84. Action of the stomata.—The guard cells serve an important func- tion in regulating transpiration. During normal transpiration the guard cells are turgid and their peculiar form then causes them to arch away from each other, allowing the escape of water vapor. When the air hecomes too dry transpiration is in excess of absorption by the roots. The guard cells lose some of their water, and collapse so that their inner faces meet in a straight line and close the stoma. Thus the rapid transpiration is checked. Some evaporation of water vapor, however, takes place through the epidermal cells, and if the air remains too dry, the leaves eventually become flaccid and droop. During the day the effect of sunlight is to increase certain sugars or salts in the guard cells so that they readily be- come turgid and open the stomates, but at night the cell-sap is less con- centrated and the stomates are usually closed. Light therefore favors transpiration, while in darkness transpiration is checked. 85. Compare transpiration from the two surfaces of the leaf.—This can be done by using the cobalt chloride paper. This paper can be kept from year to year and used repeatedly. It is thus a very simple matter to make these experiments. Provide two pieces of glass (discarded glass nega- tives, cleaned, are excellent), two pieces of cobalt chloride paper, and some geranium leaves entirely free from surface water. Dry the paper until it is blue. Place one piece of the paper on a glass plate; place the geranium leaf with the under side on the paper. On the upper side of the leaf now place the other cobalt paper, and next the second piece of glass. On the pile place a light weight to keep the parts well in contact. In fifteen or twenty minutes open and examine. The paper next the under side of the geranium leaf is red where it lies under the leaf. The paper on the upper side is only slightly reddened. The greater loss of water, then, is through the under side of the geranium leaf. This is true of a great many leaves, but it is not true of all. 86. Negative pressure.—This is not only indicated by the drooping of the leaves, but may be determined in another way. If the shoot of such a plant be cut underneath mercury, or underneath a strong solution of eosin, it will be found that some of the mercury or eosin, as the case may be, will be forcibly drawn up into the stem toward the roots. This is seen on quickly splitting the cut end of the stem. When plants in the open cannot be obtained in this condition, one may take a plant like a balsam plant from the greenhouse, or some other potted plant, knock it out of the pot, free the roots from the soil and allow to partly wilt. The stem may then be held under the eosin solution and cut. : TRANSPIRATION. 45 87. Lifting power of transpiration.— Not only does transpiration go on quite independently of root pressure, as we have discovered from other experiments, but transpiration is capable of exerting a lifting power on the water in the plant. This may Place the cut end of a leafy shoot in one end of a U tube and fit it water-tight. Partly fill this arm of the U tube with water, and add mercury to the other arm until it be demonstrated in the following w: stands at a level in the two arms as in fig. 54. Ina short time we note that the mercury is rising in the tube. 88. Root pressure may exceed transpiration.—If we cover small actively growing plants, such as the pea, corn, wheat, bean, etc., with a bell jar, and place them in the sunlight where the temperature is suitable for growth, in a few hours, if conditions are favorable, we shall see that there are drops of water standing out Fig. 54. : ; Experiment to have exuded through the ordinary stomata, or in show lifting power of on the margins of the leaves. These drops of water other cases what are called water stomata, through Pegs oh the influence of root pressure. The plant being covered by the glass jar, the air soon becomes saturated with moisture and transpiration is checked. Root pressure still goes on, however, and the result is shown in the exuding drops. Root pressure is here in excess of transpiration. This phenomenon is often to be observed during the sum- mer season in the case of low-growing plants. During the bright warm day transpiration b Ly . equals, or may be in excess of, Fig ss. root pressure, and the leaves Estimation of the amount of are consequently flaccid. As transpiration The tubes are _- htfall a h . filled with water, and as the Mightta comes on the air water transpires from the leaf becomes more moist, and the surface its movementin the tube os y : from a to 6 can be measured. Conditions of light are such (After Mangin.) also that transpiration is les- sened. Root pressure, however, is still active because the soil is still warm. In these cases drops of water may be seen exuding from the margins of the leaves due to the excess of root pressure over transpiration. Were it not for this provision for the escape of the excess of water raised by root pres- sure, serious injury by lesions, as a result of the great pressure, might result. The plant is thus to some extent a self-regulatory piece of apparatus so far as root pressure and transpiration are concerned. 89. Injuries caused by excessive root pressure. —Some varieties of toma- toes when grown in poorly lighted and poorly ventilated greenhouses suffer 46 PHYSIOLOGY. serious injury through lesions of the tissues. This is brought about by the cells at certain parts becoming charged so full with water through the activity of root pressure and lessened transpiration, assisted also probably by an accumulation of certain acids in the cell-sap which cannot be got rid of by transpiration. Under these conditions some of the cells here swell out, forming extensive cushions, and the cell walls become so weak- ened that they burst. It is possible to imitate the excess of root pressure in the case of some plants by connecting the stems with a system of water pressure, when very quickly the drops of water will begin to exude from the margins of the leaves. 90. It should be stated that in reality there is no difference between transpiration and evaporation, if we bear in mind that evaporation takes place more slowly from living plants than from dead ones, or from an equal surface of water. 91. The escape of water vapor is not the only function of the stomata. The exchange of gases takes place through them as we shall later see. A large number of experiments show that normally the stomata are open when the leaves are turgid. But when plants lose excessive quantities of water on dry and hot days, so that the leaves become flaccid, the : guard cells automatically close the Fig. 56. stomata to check the escape of water The roots are lifting more water into the plant than can be given off in the form of water vapor, so it is pressed out in the epidermis of many plants, drops. From‘ First Studies Plant Life. vapor. Some water escapes through though the cuticularized mem- brane of the epidermis largely prevents evaporation. In arid regions plants are usually provided with an epidermis of several layers of cells to more securely prevent evaporation there. In such cases the guard cells are often protected by being sunk deeply in the epidermal layer. 92. Demonstration of stomates and intercellular air spaces.—A good demonstration of the presence of stomates in leaves, as well as the presence and intercommunication of the intercellular spaces, can be made by blow- ing into the cut end of the petiole of the leaf of a calla lily, the lamina being TRANSPIRATION. 47 immersed in water. The air is forced out through the stomata and rises as bubbles to the surface of the water. At the close of the experiment some of the air bubbles will still be in contact with the leaf surface at the opening of the stomata. The pressure of the water gradually forces this back into the leaf. Other plants will answer for the experiment, but some are more suitable than others. 92a. Number of stomata.—The larger number of stomata are on the under side of the leaf. (In leaves which float on the surface of the water all of the stomata are on the upper side of the leaf, as in the water lily.) It has been estimated by investigation that in general there are 40-300 stomata to the square millimeter of surface, In some plants this number is exceeded, as in the olive, where there are 625. In an entire leaf of Brassica rapa there are about 11,000,000 stomata, and in an entire leaf of the sunflower there are about 13,000,000 stomata. 92b. Amount of water transpired by plants.—The amount of water transpired by plants is very great. According to careful estimates a sun- flower 6 feet high transpires on the average about one quart per day; an acre of cabbages 2,000,000 quarts in four months; an oak tree with 700,000 leaves transpires about 180 gallons of water per day, According to von Hih- nel, a beech tree 110 years old transpired about 2250 gallons of water in one summer, A hectare of such trees (about 400 on 2} acres) would at the same rate transpire about 900,000 gallons, or about 30,000 barrels in one summer, CHAPTER V. ’ATH OF MOVEMENT OF WATER IN PLANTS. 93. In our study of root pressure and transpiration we have seen that large quantities of water or solutions move upward through the stems of plants. We are now led to inqnire through what part of the stems the liquid passes in this upward movement, or in other words, what is the path of the ‘‘sap’’ as it rises in the stem. This we can readily see by the following trial. 94. Place the cut ends of leafy shoots in a solution of some of the red dyes.—We may cut off leafy shoots of various plants and insert the cut ends in a vessel of water to which have been added a few crystals of the dye known as fuchsin to make a deep red color (other red dyes may be used, but this one is especially good). If the study is made during the summer, the ‘* touch- me-not’’ (impatiens) will be found a very useful plant, or the garden-balsam, which may also be had in the winter from con- servatories. Almost any plant will do, however, but we should also select one like the corn plant (zea mays) if in the summer, or the petioles of a plant like caladium, which can be obtained from the conservatory. If seedlings of the castor-oil bean are at hand we may cut off some shoots which are 8-10 inches high, and place them in the solution also. 95. These solutions color the tracts in the stem and leaves through which they flow.—After a few hours in the case of the impatiens, or the more tender plants, we can see through the stem that certain tracts are colored red by the solution, and after 12 to 24 hours there may be seen a red coloration of the 458 PATH OF MOVEMENT. 49 leaves of some of the plants used. After the shoots have been standing in the solution for a few hours, if we cut them at various places we will note that there are several points in the section where the tissues are colored red. In the impatiens perhaps from four to five, in the sunflower a larger number. In these plants the colored areas on a cross section of the stem are situated in a concentric ring which separates more or less com- pletely an outer ring of the stem from the central portion. If we now split portions of the stem lengthwise we see that these colored areas continue throughout the length of the stem, in some cases even up to the leaves and into them. 96. If we cut across the stem of a corn plant which has been in the solution, we see that instead of the colored areas being in a concentric ring they are irregularly scattered, and on splitting Fig 57. Broken corn stalk, showing fibro-vascular bundles the stem we see here also that these colored areas extend for lony distances through the stem. If we take a corn stem which is mature, or an old and dead one, cut around through the outer hard tissues, and then break the stem at this point, from the softer tissue long strings of tissue will pull out as shown in fig. 57. These strings of denser tissue correspond to the areas which are colored by the dye. They are in the form of minute bundles, and are called vascular buniles. 50 PHYSIOLOGY. 97. We thus see that instead of the liquids passing through the entire stem they are confined to definite courses. Now that we have discovered the path of the upward movement of water in the stem, we are curious to see what the structure of these definite portions of the stem is. 98. Structure of the fibro-vascular bundles.—We should now make quite thin cross sections, either free hand and mount in water for microscopic examination, or they may be made with a microtome and mounted in Canada balsam, and in this condition will answer for future study. To illustrate the structure of the bundle in one type we may take the stem of the castor-oil bean. On examining these cross sections we see that there are groups of cells which are denser than the ground tissue. These groups correspond to the colored areas in the former experiments, and are the vascular bundles Fig. 58. Xylem portion of bundle. Cambium portion of bundle. Bast portion of bundle Section of vascular bundle of sunflower stem. cut across. These groups are somewhat oval in outline, with the pointed end directed toward the center of the stem. If we look at the section as a whole we see that there is a narrow continuous ring* of small cells * This ring and the bundles separate the stem into two regions, an outer one composed of large cells with thin walls, known as the cortical cells, or collectively the cortex. The inner portion, corresponding to what is called the pith, is made up of the same kind of cells and is called the med//a, or pith. When the cells of the cortex, as well as of the pith, remain thin walled the tissue is called parenchyma. Parenchyma belongs to the group ot tissues called fundamental. PATH OF MOVEMENT. 51 situated at the same distance from the center of the stem as the middle part of the bundles, and that it divides the bundles into two groups of cells. 99. Woody portion of the bundle.—In that portion of the bundle on the inside of the ring, i.e., toward the ‘ pith,” we note large, circular, or angu- lar cavities. The walls of these cells are quite thick and woody. They are therefore called wood cells, and because they are continuous with cells above and below them in the stem in such a way that long tubes are formed, they are called woody vessels. Mixed in with these are smaller cells, some of which also have thick walls and are wood cells. Some of these cells may have thin walls. This is the case with all when they are young, and they are then classed with the fundamental tissue or soft tissue (parenchyma). This part of the bundle, since it contains woody vessels and fibres, is the wood portion of the bundle, or technically the xylem. 100. Bast portion of the bundle.—If our section is through a part of the stem which is not too young, the tissues of the outer part of the bundle will show either one or several groups of cells which have white and shiny walls, that are thickened as much or more than those of the wood vessels. These cells are das? cells, and for this reason this part of the bundle is the éas/ por- tion, or the pAloem. Intermingled with these, cells may often be found which have thin walls, unless the bundle is very old. Nearer the center of the bundle and still within the bast portion are cells with thin walls, angular and irregularly arranged. This is the softer portion of the bast, and some of these cells are what are called szeve tubes, which can be better seen and studied in a longitudinal section of the stem. 101. Cambium region of the bundle.—Extending across the center of the bundle are several rows of small cells, the smallest of the bundle, and we can see that they are more regularly arranged, usually in quite regular rows, like bricks piled upon one another. These cells have thinner walls than any others of the bundle, and they usually take a deeper stain when treated with a solution of some of the dyes. This is because they are younger, and are therefore richer in protoplasmic contents. This zone of young cells across the bundle is the camdzum. Its cells grow and divide, and thus increase the size of the bundle. By this increase in the number of the cells of the cambium layer, the outermost cells on either side are continually passing over into the phloem, on the one hand, and into the wood portion of the bundle, on the other hand. 102. Longitudinal section of the bundle.—If we make thin longisections of the vascular bundle of the castor-oil seedling (or other dicotyledon) so that we have thin ones running through a bundle radially, as shown in fig. 59, we can see the structure of these parts of the bundle in side view. We see here that the form of the cells is very diflerent from what is presented in a cross section of the same. The walls of the various ducts have peculiar markings on them. These markings are caused by the walls being thicker in some 52 PHYSIOLOGY. places than in others, and this thickening takes place so regularly in some instances as to form regular spiral thickenings. Others have the thickenings AN Fig. 50. Longitudinal section of vascular bundle of sunflower stem; spiral, scalariform and pitted vessels at left; next are wood fibers with oblique cross walls; in middle are cambium cells with straight cross walls, next two sieve tubes, then phloem or bast cells. in the form of the rounds of a ladder, while still others have pitted walls or the thickenings are in the form of rings. 103. Vessels or ducts.—One way in which the cells in side view differ greatly from an end view, in a cross section in the bundle, is that they are much longer in the direction of the axis of the stem. The cells have become elongated greatly. If we search for the place where two of these large cells with spiral, or ladder-like, markings meet end to end, we see that the wall which formerly separated the cells has nearly or quite disappeared. In other words the two cells have now an open communication at the ends. This is so for long distances in the stem, so that long columns of these large cells form tubes or vessels through which the water rises in the stems of plants. 104. In the bast portion of the bundle we detect the cells of the bast fibers by their thick walls. They are very much elongated and the ends taper out to thin points so that they overlap. In this way they serve to strengthen tie stem. 105. Sieve tubes.—Lying near the bast cells, usually toward the cambium, are elongated cells standing end to end, with delicate markings on their cross walls which appear like finely punctured plates or sieves. The protoplasm in such cells is usually quite distinct, and sometimes contracted away from the side walls, but attached to the cross walls, and this aids in the detection of the sieve tubes (fg. 59.) The granular appearance which these plates pre- sent is caused by minute perforations through the wall so that there is a com- munication between the cells. The tubes thus formed are therefore called sieve tubes and they extend for long distances through the tube so that there PATH OF MOVEMENT. 53 is communication throughout the entire length of the stem. (The function of the sieve tubes is supposed to be that for the downward transportation of sub- stances elaborated in the leaves.) 106. If we section in like manner the stem of the sunflower we shall see simi- lar bundles, but the number is greater than eight. In the garden balsam the number is from four to six in an ordinary stem 3-47 diameter. Here we can see quite well the origin of the vascular bundle. Between the larger bundles we can see especially in free-hand sections of stems through which a colored solution has been lifted by transpiration, as in our former experi- ments, small yroups of the minute cells in the cambial ring which are colored. These groups of cells which form strands running through the stem are fvo- cambium strands. The cells divide and increase just like the cambium cells, and the older ones thrown off on either side change, those toward the center of the stem to wood vessels and fibers, and those on the outer side to bast cells and sieve tubes. 107. Fibrovascular bundles in the Indian corn.—We should now make a thin transection of a portion of the center of the stem of Indian corn, in order to compare the structure of the bundle with that of the plants which we have just examined. In fig. 60 is repre- sented a fibrovascular bundle of the stem of the Indian corn. The large cells are those of the spiral and reticulated and annular vessels. This is the woody por- tion of the bundle or xylem, Opposite this is the bast portion or phloem, marked by the lighter colored tissue at 7 The larger of these cells are the sieve tubes, and intermingled with them are smaller cells with thin walls. Surrounding the entire bundle are small cells with thick walls. These are elongated and the taper- Fig. 60. ing ends overlap. They are thus slender Transection of fibrovascular bundle of and long and form fibers. In such a Indian corn. a, toward periphery of stem; g, large pitted vessels; s, spiral e f z i has passed vessel; 7, annular vessel: Z, air cavity bandle allah the cemiin RS formed by breaking apart of the cells ; 7, over into permanent tissue and is said to coft bast, a form of sieve tissue; /, thin- b losed walled parenchyma. (Sachs.) e closed. 108. Rise of water in the vessels.—During the movement of the water or nutrient solutions upward in the stem the vessels of the wood portion of the bundle in certain plants are nearly or quite filled, if root pressure is active and transpiration is not very rapid. If, however, on dry days transpiration is in excess of root pressure, as often happens, the vessels are not filled with the water, but are partly filled with certain gases because the air or other 54 PHYSIOLOGY. gases in the plant become rarefied as a result of the excessive loss of water. There are then successive rows of air or gas bubbles in the vessels separated by films of water which also line the walls of the vessels. The condition of the vessel is much like that of a glass tube through which one might pass the “¢froth ’’ which is formed on the surface of soapy water. This forms a chain of bubbles in the vessels. This chain has been called Jamin’s chain because of the discoverer. 109, Why water or food solutions can be raised by the plant to the height attained by some trees has never been satisfactorily explained. There are several theories propounded which cannot be discussed here. It is probably a very complex process. Root pressure and transpiration both play a part, or at least can be shown, as we have seen, to be capable of lifting water toa considerable height. In addition to this, the walls of the vessels absorb water by diffusion, and in the other elements of the bundle capillarity comes also into play, as well as osmosis. See Organization of Tissues, Chapter 38. 110. Flow of sap in the spring.—The cause of the bleeding of trees and the flow of sap in the spring is little understood. One of the remarkable cases is the flow of sap in maple trees. It begins in early spring and ceases as the buds are opening, and seems to be initiated by alternation of high and low temperatures of day and night. It has been found that the pres- sures inside of the tree at this time are enormously increased during the day, when the temperature rises after a cold night. This has led to the belief that the pressure is caused by the expansion of the gases in the vas- cular ducts. The warming up of the twigs and branches of the tree would take place rapidly during the day, while the interior of the trunk would be only slightly affected. The pressures then would cause the sap to flow downward during the day, and at night the branches becoming cool, sap would flow back again from the roots and trunk Recent experiments by Jones e¢ a/. show that while some of the pressure is due to the expansion of gas in the tree by the rise of temperature, this cannot account for the enormous pressures which are often present, for ex- ample, when after a rise in the temperature of 2° C. there was an increase of 20 lbs. pressure. Then again, after the cessation of the flow in late spring there are often as great differences between night and day temperatures. It therefore seems reasonable to conclude that the expansion of gases by a rise in tem- perature is not the direct cause. Activities of the cells —It has been suggested by some that the rise in temperature exercises an influence on the protoplasts, or living cells, so that they are stimulated to a special activity resulting in an exudation pres- sure from the individual cells, which is known to take place. With the fall of PATH OF MOVEMENTS. 55 temperature at night this activity would cease and there might result a lessened pressure in the cells. Since the specific activities of cells are known to vary in different plants, and in the same plant at different seasons, some support is gained for this theory, though it is generally believed that the activities of the living cells in the stems are not necessary for the upward flow of water. It must be admitted, however, that at present we know very little about this interesting problem. CHAPTER VI. MECHANICAL USES OF WATER. 111. 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. 112. Restoration of turgidity in shoots.—If we cut off a iiving 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. ‘Phe end may be freshly cut again, placed ina vessel of water, covered with a bell jar and kept ina room where the temperature is suitable for the growth of the plant. The shoot will usually become turgid again from the water which is absorbed through the cut end of the stem and is carried into the leaves where the individual cells become turgid, and the leaves are again expanded. Such shoots, and the excised leaves also, may often be made turgid again by simply immersing them in water, as one of the experiments with the salt solution would teach. Fig. 61. Restoration of turgidity 113. Turgidity may be restored more certainly and (Sachs). _ ; quickly in a partially wilted shoot in another wav. The cut end of the shoot may be inserted in a U tube as shown in fig. 61, the end of the tube around the stem of the plant being made air-tight. The arm 50 TURGESCENCE. 57 of the tube in which the stem is inserted is filled with water and the water is allowed to partly fill the other arm. Into this other arm is then poured mercury. The greater weight of the mercury causes such pressure upon the water that it is pushed into the stem, where it passes up through the vessels in the stems and leaves, and is brought more quickly and surely to the cells which contain the protoplasm and cell-sap, so that turgidity is more quickly and certainly attained. 114. Tissue tensions.—Besides the turgescence of the cells of the leaves and shoots there are certain tissue tensions without which certain tender and succulent shoots, etc., would be limp, and would droop. ‘There are a number of plants usually accessi- ble, some at one season and some at others, which may be used to illustrate tissue tension. 115. Longitudinal tissue tension.—For this in early summer one may use the young and succulent shoots of the elder (sambucus); or the petioles of rhubarb during the summer and early autumn; or the petioles of richardia. Petioles of cala- dium are excellent for this purpose, and these may be had at almost any season of the year from the greenhouses, and are thus especially advantageous for work during late autumn or winter. The tension is so strong that a portion of such a petiole 10-15cm long is ample to demonstrate it. As we grasp the lower end of the petiole of a caladium, or rhubarb leaf, we observe how rigid it is, and how well it supports the heavy expanded lamina of the leaf. 116. The ends of a portion of such a petiole or other object which may be used are cut off squarely. With a knife a strip from 2-3mm in thickness is removed from one side the full length of the object. This strip we now find is shorter than the larger part from which it was removed. The outer tissue then exerts a tension upon the petiole which tends to shorten it. Let us remove another strip lying next this one, and another, and so on until the outer tissues remain only upon one side. The object will now bend toward that side. Now remove this strip and compare the length of the strips re- moved with the central portion, We find that they are much 58 PHYSIOLOGY. shorter now. In other words there is also a tension in the tissue of the central portion of the petiole, the direction of which is opposite to that of the superficial tissue. The parts of the petiole now are not rigid, and they easily bend. These two longitudi- nal tissue tensions acting in opposition to each other therefore give rigidity to the succulent shoot. It is only when the indi- vidual cells of such shoots or petioles are turgid that these tissue tensions in succulent shoots manifest themselves or are promi- nent. 117. To demonstrate the efficiency of this tension in giving support, let us take a long petiole of caladium or of rhubarb. Hold it by one end in a hori- zontal position. It is firm and rigid, and does not droop, or but little. Re- move all of the outer portion of the tissues, as described above, leaving only the central portion. Now attempt to hold it in a horizontal position by one end. It is flabby and droops downward because the longitudinal tension is removed. 118. Longitudinal tension in dandelion stems.—Take long and fresh dandelion stems. Split _-# them. Note that they coil. The longitudinal tension is very great. Place some of these strips in fresh water. They coil up into close curls because by the ab- sorption of water by the cells the turgescence of the individual cells is increased, and this increases the tension in the stem. Now place them in salt water (a 5 per cent solution). Why do they uncoil ? 119. To imitate the coiling of a tendril.—Cut out a narrow strip from a long dandelion stem. Fig. 62. ; g Strip from dandelion stem made to Fasten to a piece of soft wood, imitate a plant tendril. with the ends close together, as shown in fig. 62. Now place it in fresh water and watch it coil. Part of it coils one way and part another way, just as a ten- MECHANICAL USES OF WATER. 59 dril does after the free end has caught hold of some place for support. 120. Transverse tissue tension.—To illustrate this one may take a willow shoot 3—5cm in diameter and saw off sections about zcm long. Cut through the bark on one side and peel it off in a single strip. Now attempt to replace it. The bark will not quite cover the wood again, since the ends will not meet. It must then have been held in transverse tension by the woody part of the shoot. CHAPTER VII. STARCH AND SUGAR FORMATION 1. The Gases Concerned. 1°91, Gas given off by green plants in the sunlight.—Let us take some green alga, like spirogyra, which is in a fresh con- dition, and place one lot in a beaker or tall glass vessel of water and set this in the direct sunlight or in a well lighted place. At the same time cover a similar vessel of spiregyra with black cloth so that it will be in the dark, or at least in very weak light. 122. In ashort time we note that in the first vessel small bubbles of gas are accumulating on the surface of the threads of the spirogyra, and now and then some free themselves and rise to the surface of the water. Where there is quite a tangle of the threads the gas is apt to become caught and held back in larger bubbles, which on agitation of the vessel are freed. Fig. 63. If we now examine the second vessel Oxygen gas given off by spirogyra we see that there are no bubbles, or only a very few of them We are led to believe then that sunlight has had something to do with the setting free of this gas from the plant. 123. We may now take another alga like vaucheria and _per- form the experiment in the same way, or to save time the two may be set up at once. In fact if we take any of the green 60 STARCH FORMATION: THE GASES. 61 algze and treat them as described above gas will be given off ina similar manner. 124. We may now take one of the higher green plants, an aquatic plant like elodea, callitriche, ete. Place the plant in p the water with the cut end of the stem uppermost, but still immersed, the plant being weighted down by a glass rod or other suitable object. If we place the vessel of water containing these leafy stems in the bright sunlight, in a short time bub- bles of gas will pass off quite rapidly from the cut end of the stem. If in the same vessel we place another stem, from which the leaves have been cut, the number of bubbles of gas given off will be very few. This indicates that Fig. 64. Bubbles of oxygen gas given off from elodea in F is is a a eee large part of the gas is furnished by the (Oels.) leaves. 125, Another vessel fitted up in the same way should be placed in the dark or shaded by covering with a box or black cloth. It will be seen here, as in the case of spirogyra, that very few or no bubbles of gas will be set free. Sunlight here also is necessary for the rapid escape of the gas. 126. We may easily compare the rapidity with which light of varying intensity effects the setting free of this gas. After cutting the end of the stem let us plunge the cut surface several times in melted paraffine, or spread over the cut surface a coat of varnish. Then prick with a needle a small hole through the paraffine or varnish. Immerse the plant in water and place in sunlight as before. The gas now comes from the puncture through the coating of the cut end, and the number of bubbles given off during a given period can be ascertained by counting. If we duplicate this experi- ment by placing one plant in weak light or diffused sunlight, and another in the shade, we can easily compare the rapidity of the escape of the gas under the different conditions, which represent varying intensities of light. We see then that not only is sunlight necessary for the setting free of this gas, but that in diffused light or in the shade the activity of the plant in this respect is less than in direct sunlight. 127. What this gas is.—If we take quite a quantity of the plants of elodea and place them under an inverted funnel which is immersed in water, the gas will be given off in quite large quantities and will rise into the narrow exitot the funnel. 62 PHYSIOLOGY. The funnel should be one with a short tube, or the vessel one which is quite deep so that a small test tube which is filled with water may in this condition be inverted over the i opening of the funnel tube. With this arrange- ment of the experiment the gas will rise in the inverted test tube, slowly displace a portion of the water, and become collected in a sufficient quantity to afford us a test. When a consider- able quantity has accumulated in the test tube, we may close the end of the tube in the water with the thumb, lift it from the water and invert. Pes Nee mee The gas will rise against the thumb. A dry ae Cee ee soft pine splinter should be then lighted, and (Detmer.) after it has burned a short time, extinguish the flame by blowing upon it, when the still burning end of the splinter should be brought to the mouth of the tube as the thumb is quickly moved to one side. ‘The glowing of the splinter shows that the gas is OXVEEN, 128. It is better to allow the apparatus to stand several days in the sunlight in order to catch a full tube of the gas. Or on a sunny day carbon y dioxide gas can be led into the water in the jar from a generator, such an one as is used for the evolution of CO,. The CO, can be produced by the action of hydrochloric acid on bits of marble. The CO, should not be run below the fun- nel. The test-tube should be fastened so that the light oxygen gas will not raise it off the fun- nel. With the tube full of gas the ¢ c Fig. 66. Ready to see what the gas is. test for oxygen can be made by lifting the tube with one hand and STARCH FORMATION.—THE GASES. 63 quickly thrusting the glowing end of the splinter in with the other hand. If properly handled, the splinter will flame again. If it is neces- sary to keep the appa- ratus standing for more 2 Fig. 67. than one day it is well The splinter lights again in the presence of . oxygen gas. to add fresh water in the place of most of the water in the jar. Do not use leaves of land plants in this experiment, since the bubbles which rise when these leaves are placed in water are not evidence that this process is taking place. 129. Oxygen given off by green land plants also.—If we should extend our experiments to land plants we should find that oxygen is given off by them under these conditions of light. Land plants, however, will not do this when they are immersed in water, but it is necessary to set up rather complicated apparatus and to make analyses of the gases at the beginning and at the close of the experiments. This has been done, however, in a sufh- ciently large number of cases so that we know that all green plants in the sunlight, if temperature and other conditions are favorable, give off oxygen. 130. Absorption of carbon dioxide —We have next to inquire where the oxygen comes from which is given off by green plants when exposed to the sunlight, and also to learn something more of the conditions necessary for the process. We know that water which has been for some time exposed to the air and soil, and has been agitated, like running water of streams, or the water of springs, has mixed with it a considerable quantity of oxygen and carbon dioxide. If we bail spring water or hydrant water which comes from a stream containing oxygen and carbon dioxide, for about 20 minutes, these gases are driven off. We should set this aside where it will not be agitated, until it has cooled sufficiently to receive plants without injury. Let us now place some spirogyra or vaucheria, and elodea, or other green water plant, in this boiled water and set the vessel in the bright sunlight under the same conditions which were employed in the experiments for the evolution of oxygen. No oxygen is given off. 64 PHYSIOLOGY. Can it be that this is because the oxygen was driven from the water in boiling? We shall see. Let us take the vessel containing the water, or some other boiled water, and agitate it so that the air will be thoroughly mixed with it. In this way oxygen is again mixed with the water. Now place the plant again in the water, set in the sunlight, and in several minutes observe the result. No oxygen or but little is given off. There must be then some other requisite for the evolution of the oxygen 132. The gases are interchanged in the plants.—We will now introduce carbon dioxide again in the water. This can be done by leading CO, from a gas generator into the water. Broken bits of marble are placed in the generator, acted upon by hydro- chloric acid, and the gas is led over by glass tubing. Now if we place the plant in the water and set the vessel in the sunlight, in a few minutes the oxygen is given off rapidly. 133. A chemical change of the gas takes place within the plant cell.—This leads us to believe then that CO, is in some way necessary for the plant in this process. Since oxygen is given off while carbon dioxide, a different gas, is necessary, it would seem that a chemical change takes place in the gases within the plant. Since the process takes place in such simple plants as spirogyra as well as in the more bulky and_ higher plants, it appears that the changes go on within the cell, in fact within the protoplasm. 134. Gases as well as water can diffuse through the proto- plasmic membrane.—Carbon dioxide then is absorbed by the plant while oxygen is given off. We see therefore that gases as well as water can diffuse through the protoplasmic membrane of plants under certain conditions. 2. Where Starch is Formed. We have found by these simple experiments that some chemical change takes place within the protoplasm of the green cells of plants during the absorption of carbon dioxide and the giving off of oxygen. We should examine some of the green parts of those plants used in the experiments, or if they are not STARCH: PHOTOSYNTHESIS. 65 at hand we should set up others in order to make this examina- tion. 135. Starch formed as a result of this process.—We may take spirogyra which has been standing in water in the bright sun- light for several hours. A few of the threads should be placed in alcohol for a short time to kill the protoplasm. From the alcohol we transfer the threads to a solution of iodine in potas- sium iodide. We find that at certain points in the chlorophyll band a bluish tinge, or color, is imparted to the ring or sphere which surrounds the pyrenoid. In our first study of the spirogyra cell we noted this sphere as being composed of numerous small grains of starch which surround the pyrenoid. 136. Iodine used as a test for starch.—This color reaction which we have obtained in treating the threads with iodine is the well-known reaction, or test, for starch. We have demon- strated then that starch is present in spirogyra threads which have stood in the sunlight with free access to carbon dioxide. If we examine in the same way some threads which have stood in the dark for a few days we obtain no reaction for starch, or at best only a slight reaction. This gives us some evidence that a chemical change does take place during this process (absorption of CO, and giving off of oxygen), and that starch is a product of that chemical change. 137. Schimper’s method of testing for the presence of starch. —Another convenient and quick method of testing for the pres- ence of starch is what is known as Schimper’s method. A strong solution of chloral hydrate is made by taking 8 grams of chloral hydrate for every 5cc of water. To this solution is added a little of an alcoholic tincture of iodine. The threads of spi- rogyra may be placed directly in this solution, and in a few moments mounted in water on the glass slip and examined with the microscope. The reaction is strong and easily seen. We should also examine the leaves of elodea, or one of the higher green plants which has been for some time in the sunlight. We may use here Schimper’s method by placing the leaves directly in the solution of chloral hydrate and iodine. 66 PHYSIOLOGY. The leaves are made transparent by the chloral hydrate so that the starch reaction from the iodine is easily detected. The following is a convenient and safe method of extract- ing chlorophyll from leaves. Fill a large pan, preferably a dishpan, half full of hot water. This may be kept hot by a small flame. On the water float an evaporating dish partly ‘filled with alcohol. The leaves should be first immersed in the hot water for several minutes, then placed in the alcohol, which will quickly remove the chlorophyll. Now immerse the leaves in the iodine solution. 138. Green parts of plants form starch when exposed to light. have examined, starch is present in the green cells of those which Thus we find that in the case of all the green plants we Fig. 68. Fig. 60. Leaf of coleus showing green and white Similar leaf treated with iodine, the starch areas, before treatment with iodine. reaction only showing where the leaf Was preen. have been standing for some time in the sunlight where the proc- ess of the absorption of CO, and the giving off of oxygen can go on, and that in the case of plants grown in the dark, or in STARCH AND SUGAR: CHLOROPHYLL. 67 leaves of plants which have stood for some time in the dark, starch is absent. We reason from this that starch is the product of the chemical change which takes place in the green cells under these conditions. The CO, which is absorbed by the plant mixes with the water (H,O) in the cell and immediately forms carbonic acid. The chlorophyll in the leaf absorbs radi- ant energy from the sun which splits up the carbonic acid, and its elements then are put together into a more complex com- pound, starch. This process of putting together the elements of an organic compound is a synthesis, or a synthetic assimila- tion, since it is done by the living plant. It is therefore a syn- thetic assimilation of carbon dioxide. Since the sunlight sup- plies the energy it is also called photosynthesis, or photosynthetic assimilation. We can also say carbon dioxide assimilation, or CO, assimilation (see paragraph on assimilation at close of Chapter 10). 139. Starch is formed only in the green parts of variegated leaves.—If we test for starch in variegated leaves like the leaf of a coleus plant, we shall have an interesting demonstration of the fact that the green parts of plants only form starch. We may take a leaf which is partly green and partly white, from a plant which has been standing for some time in bright light. Fig. 68 is from a photograph of such a leaf. We should first boil it in -alcohol to remove the green color. Now immerse it in the potassium iodide of iodine solution for a short time The parts which were formerly green are now dark blue or nearly black, showing the presence of starch in those portions of the leaf, while the white part of the leaf is still uncolored. This is well shown in fig. 69, which is from a photograph of another coleus leaf treated with the iodine solution. 3. Chlorophyll and the Formation of Starch. 140. In our experiments thus far 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. 68 PHYS/OLOGY. 141. 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 photosyn- thesis 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. 142. Photosynthesis cannot take place in etiolated plants.— Moreover photosynthesis is usually confined to the green plants, and if by any means one of the ordinary green plants loses its green color this process cannot take place in that plant, even when brought into the sunlight, until the green color has ap- peared 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 on a green color, and then we find that carbon dioxide assimila- tion begins. 148. 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/orophyi/, 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. 144. Form of the chlorophyll bodies.—Chlorophyll bodies vary in form in some different plants, especially in some of the STARCH AND SUGAR: CHLOROPAYLL. 69 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 algz, illustrated in fig. 144, the chlorophyll bodies Fig. 69a. 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. 138, the chlorophyll bodies are oval in outline. These two plants, cedogonium and 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. 145. 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 70 PHYSIOLOGY. 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. 146, Chlorophyll absorbs energy from sunlight for pho‘osynthesis. —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 A7netic energy, acts on the molecules of CHO, , separating them into molecules of C, H, and O. (When the CO, from the air enters the plant cell it immediately unites with some of the water, forming carbonic acid = CII,O,.) After a series of complicated chemical changes starch is formed by the union cf carbon, oxygen, and hydrogen. In this process of the reduction of the CH,O, and the formation of starch there is a surplus of oxygen, which accounts for the giving off of oxygen during the process. 147, Rays of light concerne1 in photosynthesis, —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 Lands 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 transformed into potential energy. That is, the molecule of CH,O, is broken up, and then by a different combination of certain elements starch is formed, * 148. Starch grains formed in the chloroplasts.—During photosynthesis the starch formed is deposited generally in small grains within the green chloro- plast 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 chloro- plasts from starch which was formed in some other part of the plant, but * In the formation of starch during photosynthesis the separated mole- cules feom the carbon dioxide and water unite in such a way that carbon, hydrogen, and oxygen are united into a molecule of starch. ‘This result is usually represented by the following equation: CO,+H,0=CH,O+0,,. Then by polymerization 6(CH,O) = C,H,.0, = grape sugar. Then C,H,.0O, — H,O = C,H,.O, = starch. It is believed, however, that the process is much more complicated than this, that several different com- pounds are formed before starch finally appears, and that the formula for starch is much higher numerically than is represented by CyHy O,- STARCH AND SUGAR; CHLOROPAYLL. 71 which has passed in solution. Thus the functions of the chloroplast are twofold, that of photosynthesis and the formation of starch grains. 149. 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 /eucoplasts, and those possessing other colors, as red and yellow, in floral leaves. the root of the carrot, etc., are called chromoplasts. 150. Photosynthesis in other than green plants.—-While carbohydrates are usually only formed by green plants, there are some exceptions. Ap- parent exceptions are found in the blue-green alge, like oscillatoria, nostoc, or in the 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 energetica'ly are not the red. 151. Influence of light on the movement of chlorophyll bodies.—In fern prothallia.—If 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 hori- zontal 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 Fig. 70. Fig. 71. : Cell exposed to weak diffused light Same cell exposed to strong light, showing chlorophyll bodies along the showing chlorophyll bodies have horizontal walls. moved to perpendicular walls. Figs. 70, 71.—Cell of prothallium of fern. arranged along the surfaces of the perpendicular walls, and instead of hay- ing 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. 72 PHYSIOLOGY. 70, 71.) The same phenomenon has been observed in many plants. Light then has an influence on chlorophyll bodies, to some extent determining their position. In weak light they are arranged so that the flattened sur- faces are exposed to the incidence of the rays of light, so that the chloro- phyll will 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 elodea. The chlorophyll bodies in clodea 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 VIL STARCH AND SUGAR CONCLUDED. ANALYSIS OF PLANT SUBSTANCE. 1. Translocation of Starch. 152. Translocation of starch.—It has been found that Icaves of many plants grown in the sunlight contain starch when examined after being in the sunlight for several hours. But when the plants are left in the dark for a day or two the leaves contain no starch, or a much smaller amount. This suggests that starch after it has been formed may be transferred from the leaves, or from those areas of the leaves where it has been formed. To test this let us perform an experiment which is often made. We may take a plant such as a garden tropzolum or a clover plant, or other land plant in which it is easy to test for the presence of starch. Pin a piece of circular cork, which is smaller than the area of the leaf, on either side of the leaf, as in fig. 72, but allow i \ free circulation of air between Fig. 72. Fig. 73. 2 Leaf of tropzolum Leaf of tropzolum treated the cork and the under side of with portion covered with iodine after removal of with corks to pre- cork, to show that starch is the leaf. Place the plant vent the formation removed from the leaf dur- where it will bein the sunlight. of starch. (After ing the night. Detmer.) On the afternoon of the fol- lowing day, if the sun has been shining, test the entire leaf for starch. The part covered by the cork will not give the reaction for starch, as shown by the absence of the bluish color, while the other parts of the leaf will show it. The starch which was in that part of the leaf the day before was dissolved and removed during the night, and then during the following day, the parts being covered from the light, no starch was formed in them. 73 74 PHYSIOLOGY. 153. Starch in other parts of plants than the leaves.—We may use the iodine test to search for starch in other parts of plants than the leaves. If we cut a potato tuber, scrape some of the cut surface into a pulp, and apply the iodine test, we obtain a beautiful and distinct reaction showing the presence of starch. Now we have learned that starch is only formed in the parts containing chlorophyll. We have also learned that the starch which has been formed in the leaves disappears from the leaf or is transferred from the leaf. We judge therefore that the starch which we have found in the tuber of the potato was formed first in the green leaves of the plant, as a result of photosynthesis. From the leaves it is transferred in solution to the underground stems, and stored in the tubers. The starch is stored here by the plant to provide food for the growth of new plants from the tubers, which are thus much more vigorous than the plants would be if grown from the seed. 154. Form of starch grains.—Where starch is stored asa reserve material it occurs in grains which usually have certain characters peculiar to the species of plant in which they are found. They vary in size in many different plants, and to some extent in form also. If we scrape some of the cut surface of the potato tuber into a pulp and mount a small quantity in water. or make a thin section for microscopic examination, we find large starch grains of a beautiful structure. The grains are oval in form and more or less irregular in outline. But the striking peculiarity is the presence of what seem to be alternating dark and light lines in the starch grain. We note that the lines form irregular rings, which are smaller and smaller until we come to the small central spot termed the ‘+ hilum ”’ of the starch grain. It is supposed that these apparent lines in the starch grain are caused by the starch substance being deposited in alternating dense and dilute layers, the dilute layers containing more water than the dense ones; others think that the successive layers from the hilum outward are regularly of diminishing density, and that this gives the appearance of alter nating lines. The starch formed by plants is one of the organic substances which are manufactured by plants, and it (or glucose) is the basis for the formation of other organic substances in the plant. Without such organic substances green plants cannot make any appreciable increase of plant substance, though 4 considerable increase in size of the plant may take place. Note.—The organic compounds resulting from photosynthesis, since they are formed by the union of carbon, hydrogen, and oxygen in such a way that the hydrogen and oxveen are usually present in the same propor- STARCH: TRANSLOCATION. 75 tion as in water, are called carbohydrates. The most common carbo- hydrates are sugars (cane sugar, C,,H,,O,,, for example, in beet roots, sugar cane, sugar maple, etc.), starch, and cellulose. 155. Vaucheria.—The result of carbon dioxide assimilation in the threads of Vaucheria is not clearly understood. Starch is absent or diffi- cult to find in all except a few species, while oil globules are present in most species. These oil globules are spherical, colorless, globose and highly refringent. Often small ones are seen lying against chlorophyll bodies. Oil is a hydrocarbon (containing C, H, and O, but the H and O are in different proportions from what they are in H,O) and until recently it was supposed that this oil in Vaucheria was the direct result of photo- synthesis. But the oil does not disappear when the plant is kept for a long time in the dark, which seems to show that it is not the direct prod- uct of carbon dioxide assimilation, and indicates that it comes either from a temporary starch body or from glucose. Schimper found glucose in sev- eral species of Vaucheria, and Waltz says that some starch is present in Vaucheria sericea, while in V. tuberosa starch is abundant and replaces the oil. To test for oil bodies in Vaucheria treat the threads with weak osmic acid, or allow them to stand for twenty-four hours in Fleming’s solution (which contains osmic acid). Mount some threads and examine with microscope. The oil globules are stained black. 2. Sugar, and Digestion of Starch.* 156. The sugar produced as the result of photosynthesis may be stored as sugar or changed to starch. In general sugar is more common in the green parts of monocotyledonous plants, while starch is most frequent in dicotyledons. Plant sugars are of three general kinds: cane sugar or sucrose, abundant in the sugar cane, sugar beet, sugar maple, etc.; glucose or fruit sugar, found in the fruit of a majority of plants, and abundant in some, as in apples, pears, grapes, etc. (in many fruits and other parts of plants both glucose and cane sugar are present); and maltose, as in malted barley. 157a. Test for sugars.—Make a weak solution of pure commercial grape sugar (glucose) and also one of pure granulated cane sugar. Partly fill two test tubes with Fehling’s solution.t To one add some of the grape- sugar solution and to the other add some of the cane-sugar solution. After these tubes have stood in a warm place a few hours, it will be found that a bright orange-brown or cinnabar-colored precipitate of copper and cuprous oxide has formed in the tube containing grape sugar, while the other solu- tion is unchanged. Grape sugar or glucose therefore reduces Fehling’s solution, while cane sugar as such has no effect upon it. 157b. Test for cane sugar.—Place a small quantity of pure granulated cane sugar in a test tube and add about 15 cc. of distilled water. To * Paragraphs 156-160 were prepared by Dr. E. J. Durand. * See page 712 for formula for Fehling’s solution. 76 PHYSIOLOGY. this add 1 to 2 cc. of cobaltous nitrate solution (5 grams cobalt nitrate in 100 cc. distilled water. Keep in a stoppered bottle), then add a small quantity of a strong sodium hydrate solution (50 grams caustic soda, in sticks, to roo cc. distilled water. Keep ina bottle). A beautiful violet color appears. Test glucose or grape sugar in the same way and a blue color appears, which gradually changes to green. 157c. Cane sugar (sucrose) can be changed to glucose or invert sugar in the following way: To a weak solution of pure granulated cane sugar in a small beaker add a few drops of strong hydrochloric acid, rest on gauze wire, and boil for a minute or two over a flame. This inverts the cane sugar to glucose (equal parts of dextrose and levulose). To test for the invert sugar the acid must be neutralized. Add sodium carbonate until on adding no effervescence takes place. Now add the Fehling’s solution and boil; the red precipitate appears, showing that it reduces Fehling’s solution. 158a. Tests for sugar in plant tissue.—Scrape out a little of the tissue from the inside of a ripe apple or pear, place it with a little water in a test tube, and add a few drops of Fehling’s solution. After standing half an hour the characteristic precipitate of copper and cuprous oxide appears, showing that grape sugar is present in quantity. Make thin sections of the apple and mount in a drop of Fehling’s solution on a slide. After an hour examine with the microscope. The granules of cuprous oxide are present in the cells of the tissue in great abundance. 158). Prepare another tube with some of the pulp in 15 cc. of water; add 2 cc. of cobaltous nitrate solution, and then some of the strong sodium hydrate solution, as in paragraph 157). Cane sugar as well as grape sugar is present in these fruits. 158c. Cut up several leaves of a vigorous young Indian corn seedling in a small beaker and add 25 or 30 cc. distilled water. Boil for one or two minutes. Filter. In another small beaker boil Fehling’s solution, and if it is free from sediment (if not, filter) add a portion of the filtered corn-leaf solution and boil for two minutes. Hold the beaker toward the light and look on the bottom for the red precipitate. Filter. The red precipitate shows the presence of glucose (or invert sugar). Take the remaining portion of the corn-leaf decoction in a test tube and test for canc sugar by adding cobaltous nitrate and sodium hydrate as in paragraph 157). If the violet color does not appear at once, do not agitate it, but allow it to stand for a while. The violet color appears at the bottom of the tube, showing the presence of cane sugar, while the reaction for glucose may appear in the upper portion of the solution. For comparison take similar corn leaves, remove the chlorophyll with alcohol, and test with iodine. No starch reaction appears. The carbohydrate in corn leaves is therefore sugar and not starch. If now the grain of corn be examined the cells will be found to be full of starch grains, which give the beautiful blue reaction SUGAR: DIGESTION OF STARCH. 77 with iodine. This experiment shows that sugar is formed in the leaves of the Indian corn plant, but is changed to starch when stored in the seed. 158d. Take several leaves of bean seedlings; test for glucose and cane Sugar as in 158c. Both are present. Test a leaf for starch. It is present. 158e. Select a branch of sugar maple during autumn, winter, or spring, about 1 cm. in diameter. From a portion scrape off all the bark so as to remove all the color. Cut off some shavings of the white woody portion and boil in a small beaker for one or two minutes. Filter and test for the presence of both glucose and cane sugar as in paragraphs 158¢ and 1570. Both are present (at least in several tests made in Decemb-r, 1906). The bark is to be removed, since the coloring matter in it also reduces Fehling’s solution 158/. Scrape some pulp from the inside of a sugar beet. Mix in dis- tilled water in two test tubes. Test one for glucose and the other for cane sugar. Cane sugar is present. 159. How starch is changed to sugar. —We have seen that in many plants the carbohydrate formed as the result of carbon dioxide assimilation is stored as starch. This substance being insoluble in water must be changed to sugar, which is soluble before it can be used as food or transported to other parts of the plant. This is accomplished through the action of cer- tain enzymes, principally diastase. This substance has the power of act- ing upon starch under proper conditions of temperature and moisture, causing it to take up the elements of water, and so to become sugar. This process takes place commonly in the leaves where starch is formed, but especially in seeds, tubers (during the sprouting, etc.), and other parts which the plant uses as storehouses for starch food. It is probable that the same conditions of temperature and moisture which favor germination or active growth are also favorable to the production of diastase. 160. Experiments to show the action of diastase.—(a) Place a bit of starch half as large as a pea in a test tube, and cover with a weak solution * (about } per cent) of commercial taka diastase. After it has stood in a warm place for five or ten minutes test with Fehling’s solution. The pre- cipitate of cuprous oxide appears showing that some of tke starch has been changed to sugar. By using measured quantities, and by testing with iodine at frequent intervals, it can be determined just how long it takes a given quantity of diastase to change a known quantity of starch. In this connection one should first test a portion of the same starch with Fehling’s solution to show that no sugar is present. (b) Repeat the above experiment using a little tissue from a potato, and some from a corn seed. (c) Take 25 germinating barley seeds in which the radicle is just appear- * This solution of taka diastase should be made up cold. If it is heated to 60° C. or over it is destroyed. 73 PHYSIOLOGY. ing. Grind up thoroughly in a mortar with about three parts of water. After this has stood for ten or fifteen minutes, filter. Vill a test tube onc- third full of water, add a piece of starch half the size of a pea or less, and boil the mixture to make starch-paste. Add the barley extract. Put in a warm place and test from time to time with iodine. The first samples so treated will be blue, later ones violet, brown, and finally colorless, showing that the starch has all disappeared. This is due to the action of the dias- tase which was present in the germinating seeds, and which was dissolved out and added to the starch mixture. The office of this diastase is to change the starch in the seeds to sugar. Germinating wheat is sweet, and it is a matter of common observation that bread made from sprouted wheat is sweet. (d) Put a little starch-paste in a test tube and cover it with saliva from the mouth. After ten or fifteen minutes test with Fehling’s solution. A strong reaction appears showing how quickly and effectively saliva acts in converting starch to sugar. Successive tests with iodine will show the gradual disappearance of the starch. 161. These experiments have shown us that diastase from three different sources can act upon starch converting it into sugar. The active principle in the saliva is an animal diastase (ptyalin), which is necessary as one step in the digestion of starch food in animals. The taka diastase is derived from a fungus (Furotium oryze) which feeds on the starch in rice grains converting it into sugar which the fungus absorbs for food. The ma/t dias- tase and /eaf diastase are formed by the seed plants. That in seeds con- verts the starch to sugar which is absorbed by the embryo for food. ‘That in the leaf converts the starch into sugar so that it can be transported to other parts of the plant to be used in building new tissue, or to be stored again in the form of starch (example, the potato, in seeds, etc.). The starch is formed in the leaf during the daylight. The light renders the leaf diastase inactive. But at night the leaf diastase becomes active and converts the starch made during the day. Starch is not soluble in water, while the sugar is, and the sugar in solution is thus easily transported throughout the plant. In those green plants which do not form starch in their leaves (sugar beet, corn, and many monocotyledons), grape sugar and fruit sugar are formed in the green parts as the result of photosynthesis. In some, like the corn, the grape sugar formed in the leaves is transported to other parts of the plant, and some of it is stored up in the seed as starch. In others like the sugar beet the glucose and fruit sugar formed in the feaves flow to other parts of the plant, and much of it is stored up as cane sugar in the beet root. The process of photosynthesis probably proceeds s up to the formation of the grape sugar and in the same way in all cz fruit sugar in the leaves. In the beet, corn, etc., the process stops here, while in the bean, clover, and most dicotyledons the process is carried one step farther in the leaf and starch is formed. ANALYSIS OF PLANT SUBSTANCE. 79 3. Rough Analysis of Plant Substance. 162. Some simple experiments to indicate the nature of plant substance. — After these building-up processes of the plant, it is instructive to perform some simple experiments which indicate roughly the nature of the plant substance, and serve to show how it can be separated into other substances, some of them being reduced to the form in which they existed when the plant took them as food. For exact experiments and results it would be necessary to make chemical analyses. 163. The water in the plant.—-Take fresh leaves or Jeafy shoots or other fresh plant parts. Weigh. Permit them to remain in a dry room until they are what we call ‘‘dry.””, Now weigh. The plants have lost weight, and from what we have learned in studies of transpiration this loss in weight we know to result from the loss of water from the plant. 164. The dry plant material contains water.—Take air-dry leaves, shav- ings, or other dry parts of plants. Place them in a test tube. With a holder rest the tube in a nearly horizontal position, with the bottom of the tube in the flame of a Bunsen burner. Very soon, before the plant parts begin to ‘‘burn,”’ note that moisture is accumulating on the inner surface of the test tube. This is water driven off which could not escape by drying in air, without the addition of artificial heat, and is called ‘‘hygroscopic water.” 165. Water formed on burning the dry plant material.—Light a soft-pine or bass-wood splinter. Hold a thistle tube in one hand with the bulb down- ward and above the flame of the splinter. Carbon will be deposited over the inner surface of the bulb. After a time hold the tube toward the win- dow and look through it above the carbon. Drops of water have accumu- lated on the inside of the tube. This water is formed by the rearrangement of some of the hydrogen and oxygen, which is set free by the burning of the plant material, where they were combined with carbon, as in the cellu- lose, and with other elements. 166. Formation of charcoal by burning.—Take dried leaves, and shav- ings from some soft wood. Place in a porcelain crucible, and cover about 3 cm. deep with dry fine earth. Place the crucible in the flame of a Bun- sen burner and let it remain for about fifteen minutes. Remove and empty the contents. If the flame was hot the plant material will be reduced to a good quality of charcoal. The charcoal consists largely of carbon. 167. The ash of the plant.—Place in the porcelain crucible dried leaves and shavings as before. Do not cover with earth. Place the crucible in the flame of the Bunsen burner, and for a moment place on the porcelain cover; then remove the cover, and note the moisture on the under surface from the escaping water. Permit the plant material to burn; it may even flame for atime. In the course of fifteen minutes it is reduced to a whitish 80 PHYSIOLOGY. powder, much smaller in bulk than the charcoal in the former experiment. This is the ash of the plant. 168. What has become of the carbon t—In this experiment the air was not excluded from the plant material, so that oxygen combined with carbon as the water was freed, and formed carbon dioxide, passing off into the air in this form. This it will be remembered is the form in which the plant took the carbon-food in through the leaves. Here the carbon dioxide met the water coming from the soil, and the two united to form, ultimately, starch, cellulose, and other compounds of carbon; while with the addition of nitrogen, sulphur, etc., coming also from the soil, still other plant sub- stances were formed. 169. The carbohydrates are classed among the non-nitrogenous sub- stances. Other non-nitrogenous plant substances are the organic acids like oxalic acid (H,C,O,), malic acid (H,C,H,O,), etc.; the fats and fixed oils, which occur in the seeds and fruits of many plants. Of the nitrogenous substances the proteids have a very complex chemical formula and contain carbon, hydrogen, oxygen, nitrogen, sulphur, etc. (example, a/euron, or proteid grains, found in seeds). ‘The proteids are the source of nitrogenous food for the seedling during germination. Of the amides, asparagin (C,H;N,O,) is an example of a nitrogenous substance; and of the alkaloids, nicotin (C,,H,,N,) 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 80 per cent, and many water-plants and fungi as much as 95 per cent of their weight.’’ When heated to roo® C. the water is driven off. The dry matter remaining is made up partly of organic compounds, exam- ples of which are given above, and inorganic compounds. By burning this dry residue the organic substances are mostly changed into volatile prod- ucts, principally carbonic acid, water, and nitrogen. The inorganic sub- stances 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 percentage 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. | ‘ it ahs | oe é j so v ou Bs v G ; | 88] eb | Ba] z : 3 a v es l[eok | aS | & G od Le} & OD: FA one) os) ae a a o | 6 aa ae Oo | og 3 Tel