Ag are CORNELL UNIVERSITY. THE Koswell P. Flower Library THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF THE N. Y. STATE VETERINARY COLLEGE. 1897 pos University Library wii lin ‘al morphology. il Cornell University 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://www.archive.org/details/cu31924001011448 EXPERIMENTAL MORPHOLOGY Mtoe 189 EXPERIMENTAL MORPHOLOGY BY CHARLES BENEDICT DAVENPORT, Pu.D. INSTRUCTOR IN ZOOLOGY IN HARVARD UNIVERSITY PART SECOND EFFECT OF CHEMICAL AND PHYSICAL AGENTS UPON GROWTH Nef Work THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Lrp. 1899 All rights reserved Fo: Rea CopPyRiGuHT, 1899, By THE MACMILLAN COMPANY. Nortoood J3regs 1 §. Cushing & Co. — Berwick & Smith Norwood Mass. U.S.A PREFACE TO PART II DEVELOPMENT consists of growth and differentiation, accom- panied in the larger organisms by nuclear- and cell-division. The present Part deals with growth. The importance of the study of growth cannot be over- estimated, and it is a cause for wonder that the treatment of the subject has been so much neglected by text-books. Indeed, it is a surprising fact that it has not been thoroughly and sys- tematically investigated. For, in last analysis, the maintenance of the human race depends upon that property which protoplasm among all substances alone displays of increasing itself for an indefinite time and to an indefinite amount. And the possibil- ity of increasing the human race beyond limits that are not far off depends upon a better knowledge of the conditions of growth. The reader has only to consider that the world’s supply of 2500 million bushels of wheat, 2000 million bushels of maize, 90 million tons of potatoes, and its untold millions of tons of beef, pork, and fish are reproduced each year by growth. The mineral matters of the soil are being washed out into the sea and are largely lost, but the capacity of growth under appropriate conditions is never lost; it redoubles as the amount of the growing substance is increased. The only thing, then, which limits growth is the limitations in the conditions of growth. What are these conditions? This is the important question to which attention has been directed in this Part. Aside from this practical interest, the study of growth is important as bearing on the question of the dependence of vital activities, and especially development, upon external conditions, xa xb PREFACE and the possibility of the control of development by appropri- ately altering those conditions. Growth phenomena show them- selves, indeed, particularly susceptible to this control, and are consequently especially valuable for experimental study. In the preparation of the Second Part, I have been put again under heavy obligations to my friend and colleague, Dr. G. H. PARKER, who has read most of the manuscript and made important suggestions. I am also indebted to Dr. H. E. Saw- YER for reading Chapter XI in the manuscript, and to my wife for much painstaking work on the manuscript and proofs and for compiling the index. Cc. B. D. CAMBRIDGE, Mass., Dee. 11, 1898. CONTENTS CHAPTER X Intrropuction: On NormMat GrowtH CHAPTER XI Errect oF CHEMICAL AGENTS UPON GROWTH § 1. Effect of Chemical Agents upon the Rate of Growth 1. The Materials of which Organisms are composed a. Analysis of the Entire Organism b. Detailed Account of the Various Elements siwad as Food Oxygen, 304; Hydrogen, 306; Carbon, 306; Nitro- gen, 307; Phosphorus, 313; Arsenic, Antimony, and Bismuth, 314; Sulphur, 314; Chlorine, 316; Bromine, 316; Iodine, 317; Fluorine, 317; Lith- ium, 318; Sodium, 318; Potassium, 318; Rubidium and Cesium, 320; Strontium, 321; Manganese, 321; Tron, 321; Magnesium, 323; Silicon, 324; Copper, 824. 2. The Organic Food used by Organisms in Growth . a. Fungi . . F bd. Green Plants c. Animals . Ameeba, 328; Ariphibts, 329; Masiineads 330. 3. Growth as a Response to Stimuli : a. Acceleration of Growth by Chemical Stimulants : b. The Election of Organic Food § 2. Effect of Chemical saat upon the Direction of Cravih = Chem. tropism : 1. Chemotropism in ili ‘Tentacles of Tnsectivorans Plante 2. Chemotropism of Roots . 3. Chemotropism of Pollen-tubes 4. Chemotropism of Hyphe 5. eles of ae aaa Ties § in Spirogyra Literature : xv PAGE 281 293 294 296 304 324 324 326 327 331 331 333 335 335 336 337 340 342 343 XV1 CONTENTS CHAPTER XIi Tue Errect oF WATER UPON GROWTH § 1. Effect of Water upon the Rate and Quantity of Growth § 2. Effect of Water on the Direction of Growth — Hydrotropism Roots . : 3 : : 2. Rhizoids of Hignes Cryptogams 3. Stems : 4. Pollen-tubes 5. Hyphe of ee Literature : a CHAPTER XIII EFFECT OF THE DENSITY OF THE MEDIUM UPON GROWTH § 1. Effect of Density upon the Rate of Growth Literature : ‘ CHAPTER XIV Errect or Morar AGENTS UPON GROWTH § 1. Effect of Molar oe upon the Rate of Growth . 1. Contact ‘ i ‘ 2. Rough Movements . 3. Deformation 4. Local Removal of aissite: § 2. Effect of Contact upon the Direction of Growth — ‘Thiemets apaih 1. Twining Stems 2. Tendrils . 3. Roots 4. Cryptogains 5. Animals 6. The Accumulation of Gontaet: stinnlus aad Aestienatinstion to it 7. Explanation of Hiern opism § 3. Effect of Wounding upon the Direction of Gomi — Hema: tropism : ¥ : - 1. False ‘ign nwptie 2. True Traumatropism § 4. Effect of Flowing Water upon the Piscean. of Growth Thee. tropism é e é Summary of the Chapter Literature PAGE 350 355 356 357 358 358 358 360 362 369 370 370 370 372 3875 376 376 377 380 381 382 382 383 384 384 384 387 388 389 CONTENTS CHAPTER XV EFrrect oF GRAVITY UPON GROWTH § 1. Effect of Gravity upon the Rate of Growth § 2. The Effect of Gravity upon the Direction of Growth — ectroptann 1. False Geotropism 2. True Geotropism u. Roots b. Stems c. Rhizoma . d. Cryptogams e. Animals . jf. After-effect in Géotn cules Summary i Literature CHAPTER XVI Errect oF ELECTRICITY UPON GROWTH § 1. Effect of Electricity upon the Rate of Growth § 2. Effect of Electricity upon the Direction of Growth— Blecite. Be Ce Or 5. tropism False and ‘Tous Blentidtrs opism Electrotropism in Phanerogams Electrotropism in Other Organisms Magnetropism . Explanation of fileewatne opism and Simmaty Literature CHAPTER XVII Errect or Ligut upon GRowTH § 1. Effect of Light on the Rate of Growth . 1. 9 3. 4. Retarding Effect of Light Accelerating Effect of Light . The Effective Rays . u. The Effective Rays in the Reta aation of Gr ea by Ge b. The Effective Raysin the Acceleration of Growth by Light The Cause of the Effect of Light on the Rate of Growth § 2. Effect of Light upon the Dirertion. of Growth — Phototropism 1. 2. Plants Animals a. Serpulidz b. Hydroids . Xvii PAGE 391 391 392 392 392 397 398 398 398 401 402 403 405 409 409 409 411 412 413 413 414 416 416 423 427 427 432 436 437 437 442 442 443 XViil CONTENTS 3. General Considerations a. Persistence of Stimulation b. Acclimatization to Light c. Mechanics of Phototropism Literature CHAPTER XVIII Errect oF Heat on GrRowTH § 1. Effect of Heat on the Rate of Growth 1. Plants ; ; : 2. Animals . : : ‘ 38. Some General Pleasaebn sroeitipensjiun Heat Hitedis. a. Latent Period . b. Sudden Change of ‘Temperature c. Cause of Acceleration of Growth by Heat § 2. Effect of Heat on the Direction of Growth — Thermotropism 1. Effect of Radiant Heat . : é : ; 2. Conducted Heat 3. Causes of Thermotropism Summary of the ii ae Literature : CHAPTER XIX Errect or ComMpLex AGENTS UPON GROWTH, AND GENERAL CONCLUSIONS . The Coéperation of Geotropism and ceca te . Effect of Extent of Medium on Size Dr Ur wr woe External Agents 1. Modification of Rate of Gacath 2. Modification of Direction of Growth — ‘Tropismn 3. Adaptation in Tropisms . : i : 4. Critical Points in Tropism Literature List or TABLES IN Parts I anv II . InpEx TO Parts I anp II . . General Considerations relating to the Action upon Gr omits of PAGE 444 444 444 444 445 450 450 457 460 460 460 461 463 463 464 466 467 407 470 473 478 478 480 484 484 486 489 493 Part II THE EFFECT OF CHEMICAL AND PHYSICAL AGENTS UPON GROWTH ——0t9400—_. CHAPTER X INTRODUCTION: ON NORMAL GROWTH ORGANIC growth is increase in volume.* It is not develop- ment; it is not differentiation; it is not increase in mass, although the latter may often serve as a convenient measure of growth. In analyzing the processes of growth in organisms we must recognize at the outset that organisms are composed of living matter and formed substance, and that growth may therefore result from the increase in volume of either of these. The living matter, in turn, is composed of two principal substances : | the plasma and the enchylema or cell sap; so growth may be. due to the increase of either of these substances, — may result either from assimilation, or more strictly from the excess of * Growth has been variously defined. Thus Huxtey has called growth ‘‘increase in size,’? which is essentially the same as my definition. Sacus (°87, p. 404) defines growth as an increase in volume intimately bound up with change of form (‘‘eine mit Gestaltveranderung innig verkniipfte Volumen- zunahme’’); and he illustrates the definition by the example of the growth of a sprout from its beginning to its full development. In this case two phenom- ena are distinguishable: first, increase in volume, and, second, the filling out of the details of form. As Sacus says, these phenomena taken together are gen- erally denominated ‘‘development’’; and it seems decidedly advantageous to retain this word with its usual signification, and to distinguish the two compo- nent processes by the terms growth and differentiation. Prerrer’s (’81, p. 46) definition differs still more widely from the one pro- posed above. He defines growth as change in form in the protoplasmic body (‘‘die gestaltliche Aenderung im Protoplasmakorper’’) ; and he goes on to say that increments of volume and mass are not proper criteria of growth. Prrerrer illustrates this statement by the following example: A plant stem or a cell mem- 281 282 INTRODUCTION [Cu. X. the constructive over the excretory processes of the plasma, or from the taking in of water.* Of the three factors involved in growth— increase of formed substance, of plasma, and of enchylema— the part played by the last seems to me to have been underestimated. Plant physiol- ogists have been in the best position to acquire the facts. brane can be permanently elongated by extension beyond the limits of elasticity without the volume necessarily increasing;—and he apparently means to include such an artificial deformation in his definition of growth. ‘And,’ he continues, ‘‘ under certain circumstances a diminution of volume of a plant seg- ment can indeed occur as a result of growth, when, for example, the elasticity of the wall is increased by growth and water is pressed from the cell until equi- librium is restored.’” It may be doubted, however, if Prerrer would say that. in this case the cell, as a whole, had grown ; but if he would, then his definition is a wide departure from ordinary usage. Also, Vines (’86, p. 291) offers a definition, which is intermediate between that of Sacus and thatof Prerrer. ‘By growth,’’ he says, ‘‘ we mean per- manent change of form, accompanied usually by increase in bulk.’? But then he goes on to say, ‘Nor does this increase even of the organized structures of an organ, that is of the protoplasm and the cell wall, necessarily imply that it is growing. Thus, an increase of the cell wall may take place without any appre- ciable enlargement of the cell, as, for instance, when a cell wall thickens.’? But since the thickening is a ‘‘ permanent change of form,”’ it should be consid- ered by the author a growth process were not increase in size of the cell after all, in the author’s mind, the most important criterion of its growth. Finally, Frank (’92, p. 855) finds no other criterion for growth than an increase in vol- ume (dependent, however, upon the increase of a particular substance). Thus, with these different plant physiologists, we see the word growth bearing the ideas of increase of volume and differentiation, then of differentiation alone, and, finally, of increase of volume alone. * Various analyses of the process of growth have been made by different authors. Let us look at a few of these opinions. Says Huxxey (°77, p. 2), ‘growth is the result of a process of molecular intussusception.” According to N. J. C. Mituer (’80, p. 100), ‘* all phenomena of growth depend, in last analy- sis, upon this, that the molecule of the solid substance is introduced into the region of growth.” Frank (92, p. 355) understands by growth that increase of volume which consists of the apposition or intussusception of new solid mole- cules of similar matter (‘‘ welche auf der An- oder Hinlagerung neuer fester Molekule gleichartigen Stoffes beruhen’’). According to Verworn (795, p. 475), growth is due to the excess of assimilation over disassimilation. These defi- nitions include what I regard as only half the process of growth. On the other hand, Drisscn (94, p. 37) distinguishes two kinds of cell growth: (1) passive growth, due to imbibition of water, and (2) active growth, resulting from assimilation. This classification agrees with the one I have pro- posed, but I think the term passive growth very inapt, since the imbibition of water is as truly an active process as any other vital activity. Int.] ON NORMAL GROWTH 283 They have recognized in the tip of the plant three growth regions. At the extreme tip of the stem (or radicle) is the region of rapid cell division but comparatively slow growth ; next below is the 15 wm. zone exhibiting the Grand Period of 10 growth; and_ still 7 below is the zone of ra histological differ- ms J entiation (Fig. 75). eZ In the first zone a] growth of plasma 1 % 3 4 o 6 7 8 y 10 DAYS is occurring ; in the Fic. 75. — Curve of daily growth in length of a disc, second zone growth originally 1 mm. long, and taken immediately behind " the vegetation point of a radicle of Phaseolus. It of the enchylema 1s comes to occupy in successive days the three zones chiefly taking place; referred to in the text. From Sacus, Lectures on Plant Physiology. in the third zone there is growth of formed substance. The immense preponderance of the growth of the second period (at 7 days) is an index to the preponderat- ing influence in growth of the imbibition of water. XN. Le . A 0.2 at pbsessssenaee = 05 lO 1s 20 25 30 35 40 45 50 55 60 65 7.0 <= I Fic. 76.— Curve representing the intensity of growth of roots of Pisum sativum, ———; Vicia sativa, -------- ; and Lens esculenta, —-—-—-— , the time being assumed to be constant. The length of the abscissex in the direction from left to right corresponds to the distance, in millimeters, of the marked spaces on the root from the root apex. The ordinates correspond to the amount of growth, in milli- meters, of the corresponding piece of the root after 20 hours. From CIESIELSKI (’72.) That which occurs with one and the same piece of the stem on successive days takes place simultaneously at the different zones of the growing organ. Thus in the radicle (Fig. 76) 284 INTRODUCTION [Cu. X. we find during a period of 20 hours little growth occurring at the root tip, a maximum of growth at 8 or 4 millimeters from the tip, and further up less growth, until a zone of almost no growth is reached. An analysis of the substance of the stem at different levels below the tip reveals the same thing —a sudden increase in the amount of water ; from 738% at the | es i tip to 88% at the | first internode (ID), . A reaching a maxi- il ‘mum at 938% in the\ Fa second _ internode | #08 CII), then falling ; a oe oY x slightly (92.7) to Fic. 77.— Curve showing the percentage of water in suc- the fifth internode cessive internodes of hothouse plants of Heterocen- jf tron roseum Hook. et Arm., about 4 decimeters high. (VI, Fig. TT) . The The ordinates indicate the percentage of water at experiments and ob- each internode from the terminal bud (I) to the fifth a (VI). (From Kraus, °79.) servations upon which these conclu- sions rest thus agree in assigning the chief role to water in the ' growth of plants. While the fact that water constitutes a large proportion of the growing animal was made known by the classical researches of BAUDRIMONT and Martin Sarnt-ANGE (51), the impor- tance of the part which it plays in the growth of animals seems first to have been appreciated by Lorp (92, p. 42), who showed how in the withdrawal of water by plasmolytic meth- ods growth was interfered with. Later I made a series of determinations of the relative part played by water and dry substance in the growth of an animal (tadpole). Eggs and embryos at various ages were weighed after removal of super- ficial water. Then they were kept in a desiccator from which air had been pumped and which contained a layer of sulphuric acid to absorb moisture. After repeated weighings a condition was found in which the drying mass lost no more water (con- stant weight). The total diminution in weight indicated the mass or volume of free water contained in the organism at the beginning of the experiment. Numerous weighings were’ Int.] ON NORMAL GROWTH 285 made during two seasons upon Amblystoma, toads, and frogs. All series showed the same thing; the most complete series is that given in the following table : — TABLE XXII Emepryros or Frogs. 1895* WEIGHT oF Dry ieee Days AFTER AVERAGE " Suusrance, WEIGHT OF %o oF Hatcuinc. |WeEiGuT, in Me. In Me. Water in Me.| Water. May 2 1 1.83 80 1.03 56 “3 2 2.00 83 1.17 59 re 0 5 3.43 -80 2.63 17 i 8 7 5.05 54 4.51 89 “10 9 10.40 72 9.68 93 “15 14 23,62 1.16 22.36 96 June 10 41 101.0 9.9 91.1 90 July 23 84 1989.9 247.9 1742.0 88 These results are graphically represented in Fig. 78. The curve and table show that, exactly as in plants, there is a 1007 90% 4 pe | 80% 70% 60% ] Jo% Days, 10 20 30 Ev) so 60 70 60 90 Fic. 78.— Graphic representation of last column of Table, showing percentage of water in frog embryos from 1 to 84 days after hatching. Compare with Fig. 77. period of slow growth accompanied by abundant cell division —the earliest stages of the egg. Then follows, after the first * Compare with the less complete table of Bauprimont and Martin Sarnt- Ance, 751, p. 582. 286 INTRODUCTION (Cu. X few hours, a period of rapid growth due almost exclusively to imbibed water, during which the percentage of water rises from 56 to 96; lastly comes the period of histological differen- tiation and deposition of formed substance, during which the amount of dry substance increases enormously, so that the per- centage of water falls to 88 and below. But the growth is due chiefly to imbibed water. The foregoing facts thus unite in sustaining the conclusion that at the period of most rapid growth of organisms growth is effected by water more than by assimilation. In later development the proportion of water slowly falls. This fact is well brought out in the following tables : — TABLE XXIII SHOWING THE PERCENTAGE OF WATER IN CHICK EMBRYOS AT VARIOUS STAGES up To HaTcHING, FROM Ports, °79 Hours or Broopine. ABSOLUTE WEIGHT IN GRAM. % Water. 48 0.06 83 54 0.20 90 58 0.33 88 91 1.20 83 96 1.80 68 124 2.03 69 264 6.72 59 TABLE XXIV SHOWING THE PERCENTAGE OF WATER IN THE HuMAN EmBrro aT VARIOUS Staces up To Birru, FROM FEnLING, '77 AGE IN WEEKES. ABSOLUTE WEIGHT IN GRAM. % Water. 6 0.975 97.5 17 36.5 91.8 22 100.0 92.0 24 242.0 89.9 26 569.0 86.4 30 924.0 83.7 35 928.0 82.9 39 1640.0 74.2 Int.] ON NORMAL GROWTH 287 These results indicate that during later development growth is largely effected by excessive assimilation or by storing up formed substance. From another standpoint we can recognize two kinds of growth: one a transitory growth, after which the enlarged organ may return again to its former size, and the other a per- manent or developmental growth, which is a persisting enlarge- ment, and plays an important part in development. As an example of transitory growth may be cited the case of the Sen- sitive Plant, whose leaflets when touched turn upwards as a result of the growth of cells on the convex side; but this enlargement is only temporary—it is transitory growth. This phenomenon is indeed usually not included in the idea of growth ; yet it is well-nigh impossible to draw a sharp line of distinction between it and permanent growth. For example, when a tendril of the Passion Flower is touched it may curve as a result of growth of the cells on the convex side, and this curvature may later become obliterated, as in the case of the Sensitive Plant; but the longer the contact is continued the more the cells enlarge, and the more their walls become perma- nently modified. Thus the condition of temporary growth shades insensibly into that of permanent growth. So far as possible we shall consider in this book only developmental growth. Still another classification may be made of the phenomena of growth. We.may distinguish between diffused and localized growth. In diffused growth the entire individual or many of its parts are involved. In localized growth the process is con- fined toa limited region. Thus in the early development of the frog diffused growth occurs, while in the formation of the appendages we have an example of localized growth. Since localized growth is an important factor in differentiation, many of the data concerning this phenomenon will be first considered in the Part dealing with Differentiation. Normal growth may or may not be accompanied by cell-divi- sion. - But usually cell-division occurs sooner or later in the growing mass. The act of cell-division seems to retard the process of growth. This conclusion follows from some experi- ments of WARD (’95, p. 3800) on the growth of bacteria, which 288 INTRODUCTION [Cu. X are summarized in the curve, Fig. 79. This shows how the growth in length of the bacterial rods is delayed at intervals MOMENT WHEN 4TH] SEPTUM Was CLEARLY VISIBLE, GROWTH AT MAXM. | MOMENT| WHEN 8D SEPTUM | AS VISISLE, GROWTH “ MAXM, 70-03 y res MOMENT WHEN 2D SEPTUM AS FIRST VISIBLE,| (an GROWTH AT MAXM, 60 LL £4. MOMENT WHEN 1ST SEPTUM nn “86 WAS DISTINCTLY VISIBLE, 56-22 GROWTH AT MAXM.! v Es + Be 50°76 |_ 5 3 a 43-48 t PERIOD OF MINM: GROWTH, ne 730-84 & 47H CELL DIVISION. at 36-2 30 32:56 34°38 THIRD PERIOD OF MINM, GROWTH, Be — 29-12 WHEN 8D DIVISION 27-30 } TOOK PLACE. 20 | # 2 2 a] E: : 5 S Ss 2 mea Ala a 3 3 12-40 12-50 Be aa g 12-47 bs =} i=} a a Boat og a SECOND PERIOD OF MINM>GROWTH,S3 PERIOD OF MINM, GROWTH, WHE RIEDIGELLCOIVISION, oe & WHEN FIRST CELL DIVISION OCCURRED. OCCURRED. Fic. 79. — Curve of growth of a bit of a filament of Bacillus ramosus, 27.30 & long at the beginning and 70.88 » at the end of the period of observation. The curve shows certain periods of diminished growth (indicated by the arrows below the curve), which correspond to cell-division. From Warp (’95, p. 300). by the nuclear divisions and the accompanying formation of transverse septa.* 4 The course of. aT normal growth may va now be studied in 20 MM. * Attention may here be called to aphenomenon which has_ repeatedly been observed when a single growing mammal has been weighed at an regular intervals. This is a sort of alternation of periods of unusually rapid growth with periods of diminished growth, the interval being a day or two. There is an irregu- 20 40 60 80 io = larity in the length of Fic. 80. — Curve of length of shell of Lymnza stagnalis these periods. See Sarnt- at intervals from hatching up to 85 days. From Lovur, ’93; compare also Semper, Animal Life, p. 163. Minor, 91, Table XIV. Int] ON NORMAL GROWTH 289 the case of certain selected, typical organisms. This may be most quickly done by the use of curves whose abscisse represent time intervals and whose ordinates represent size or weight. Figures 80, 81, and 82 are such curves. In all cases excepting that of guinea pig (in which the curve represents the growth of only a comparatively late developmental period, namely, from birth onward) the curves exhibit one characteristic shape. The absolute increments are not, however, shown directly by these curves. To obtain them one must transform the curves into others in which the successive ordinates shall “ — represent the absolute incre- ment of weight over the last preceding. Underthese * Y circumstances the absolute HI increments rapidly reach a maximum from which they decline to zero.* \ Why does the growth de- \ cline to zero? Thetheory , 0% has been suggested + that / 6% 4% KILOGRAMS ~ there is a “certain impulse . . . A given at the time of im- Wve pregnation which gradually : aps Fic. 81.—The continuous line (a) represents fades Out so that from the weights in fractions of a kilogramme the beginning of the new attained by guinea pigs from birth until growth there occurs a 12 months old. The broken line (b) rep- she ; F resents the daily percentage increments diminution in the rate of (%’s at the right) of the same guinea pigs growth.” The facts of up to7 months. After Minot (’Y1). * Another method of representing curves of growth has been proposed by Professor Minor (’91, p. 148), who argues that for a given period the rate of growth should be expressed as the fraction of weight added during that period ; for, he says, ‘‘the increase in weight depends on two factors: first, upon the amount of body substance, or, in other words, of growing material present at a given time ; second, upon the rapidity with which that amount increases itself.’ Such a curve of percentage daily increments is given for the guinea pig in Fig. 81. Since, however, the greater part of the ‘‘ body substance”? at its period of greatest growth is not ‘‘ growing material,’’ as assumed, but water, the peculiar value of the curve of percentage increments is doubtful. + By Minor, ’91, p. 151. bug INTRODUCTION 290 (Cu. X growth in the tip of the plant do not, however, support this theory, for the protoplasm at this point may go on growing for centuries, as we see in the case of trees. Some of the protoplasm at the tip is, how- ever, constantly falling back a to form part of the stalk: aye this part soon ceases to grow, v : undergoing histological dif- _ / ferentiation. The reason why the animal ceases at length to grow is the same as the reason why the differ- 60 MM. 50 mY 7 entiated tissue below the tip / . we of the epicotyl ceases to grow er ae : ‘ sw —not because there is a nec- Fic. 82.—Curves of growth of Phaseolus essary limit to growth force multiflorus (continuous line) and Vicia faba (broken line). The ordinates rep- resent actual lengths attained on the respective days by a bit of stem origi- nally 1mm. long. After Sacus, Lect- ures on Plant Physiology. at a certain distance from impregnation, but because it is in the nature of the species that the individual should cease to grow at this point. The indefinite growth of this part, the limited growth of that, are as much group characters as any structural quality. To recapitulate briefly : Growth is increase in size, and may result from increment of either the formed substance through secretion, the plasma through assimilation, or the enchylema through imbibition. This increment may be either transitory or permanent; the latter class chiefly concerns us_ here. Growth may be either diffused throughout the entire organism, or local, forming a factor of differentiation. In normal growth the increase is at first slow, then rapidly increases to a maxi- mum, and, finally, in most animals, diminishes to zero. This final cessation is a special quality of certain organisms, to be explained like structural qualities, on special grounds. oOo me ao Int.] ON NORMAL GROWTH 291 0 1 2 3 4 5 6 7 8 ae LA a VA A VY oan a Fa WA VA Lt ta / / | Fi —“ = Fic. 83.— Curve of growth of man. The ordinates represent weight in kilogrammes. The prenatal part of the curve is constructed from the data of FEHLING (’77) ; the postnatal part from QuETELET (’71) for the male. The curve of the first twelve months of postnatal life is adapted from Gatton (’84). LITERATURE Bauprimont, A., and G. T. Martin Sarnt-ANGE, ’51. Recherches anato- miques et physiologiques sur le développement du foetus et en parti- culier sur l’évolution embryonnaire des oiseaux et des batrachiens. Mém. presentés par divers savants a ]’Acad. des Sci. de l’Inst. Nat. de France. XI, 469-692. 18 pls. or A 292 INTRODUCTION [Cu. X L Driescu, H. ’94. Analytische Theorie der organischen Entwicklung. Leip- zig. Engelmann, 185 pp. 1894. Feu ine, H. 77. Beitrige zur Physiologie der placentaren Stoffverkehrs. Arch. f. Gyniikologie. XI, 523-557. Frank, A. B.’92. Lehrbuch der Botanik nach dem gegenwartigen Stand der Wissenschaft bearbeitet. I.Band. Leipzig. 1892. Gatton, F.’84. Life History Album. 172 pp. London. 1884. Huxuey, T. H.’77. A Manual of the Anatomy of Invertebrated Animals. 698 pp. London. 1877. Kraus, G. "79. Ueber die Wasservertheilung in der Pflanze. Festschr. z. Feier des Hundertjahrigen Bestehens d. Naturf. Ges. in Halle. pp. 187-257. Loss, J.’92. Untersuchungen zur physiologischen Morphologie der Thiere. II. Organbildung und Wachsthum. 82 pp.2 Taf. Wirzburg. 1892..2:)+ 7! Minor, C. S. 91. Senescence and Rejuvenation. Jour. of Physiol. XII, 97-153. Plates 2-4. Miu.ter, N. J. C. ’80. Handbuch der allgemeinen Botanik. I. Theil. Heidelberg. 1880. Prerrer, W.’81. Pflanzenphysiologie. Engelmann. Leipzig. 2 Bde. 383 +474 pp. ee Potr, R. 79. Untersuchungen iiber die chemischen Veriinderungen im Hiihnerei wihrend der Bebriitung. Landwirth. Versuchs-Stat. XXIII, 203-247. QUETELET, A. ’71. Anthropométrie ou mesure des différentes facultés de Vhomme. 479 pp. 2 pls. Bruxelles and Paris. 1871. 4 Sacus, J. ’87. Vorlesungen iiber Pflanzenphysiologie. Leipzig. Engel- mann. 884 pp. 1887. Sarnt-Loup, R.’93. Sur la vitesse de croissance chez les Souris. Bull. Soc. Zool. de France. XVIII, 242-245. ~ VeErwory, M. ’95. Allgemeine Physiologie. 584 pp. Jena: Fischer. 1895. Vinss, 8. H.’86. Lectures on the Physiology of Plants. Cambridge [Eng.] Univ. Press. 710 pp. 1886. Warp, H. M.’95. (See Chapter XVII, Literature.) CHAPTER XI EFFECT OF CHEMICAL AGENTS UPON, GROWTH WE shall consider this subject under two heads: (1) Effect upon the rate of growth, and (2) Effect upon the direction of growth. § 1. Errect or CHEMICAL AGENTS UPON THE RATE OF GROWTH Organic growth, occurring in a material composed of water, plasma, and formed substance, consists in the increment of each of these components. The means and results of varying the quantity of water in the organism will be discussed in the next chapter ; here we are to consider the results of assimilation, including the production of formed substance. The scope of our work may be more precisely defined as the answer to the question, What réle do the various chemical substances (exclud- ing water) play in the metabolic changes involved in growth ? There are two réles played by chemical substances in the body; and, accordingly, we may distinguish two kinds of chemical agents having diverse effects upon growth. These agents — foods, in the widest sense of the word — must supply the material—the atoms— from which the molecules of the plasma, or of its formed substance, are made up; and, sec- ondly, they must supply energy for metabolism. Foods, then, yield to the organisms matter and motion; they are hylogenic (plastic) and thermogenic (respiratory). These two offices of chemical agents in growth are only in certain cases exerted by distinct kinds of food. In the case of animals, sodium chloride and iron compounds are examples of wholly plastic foods, while the free oxygen taken into the body is chiefly thermogenic. In the case of the free oxygen, how- ever, it is quite probable that it is sometimes used in the con- struction of the molecule of active albumen which, according 293 294 EFFECT OF CHEMICAL AGENTS (Cu. XI to Lorw, constitutes the essential living substance. For exam- ple, oxygen performs this office in LoEw’s (96, p. 39) hypoth- esis of the formation of albumen in plants from the nitroge- nous products which result from the action of an enzyme upon the reserve proteids, z.e. leucine. Thus leucine formaldehyd C,H,,NO, +70 =2C0, +H,0 +4CH,0 + NH,. formaldehyd asparagin 4CH,O + 2NH,+ 0, = C,H,N,0,+ 3 H,0. Now since, as LoEw makes probable, asparagin is a stage in the production of albumen, the free oxygen molecule may be essential to the synthesis of the living substance. The facts indicate that the plastic and thermogenic functions of foods are inextricably intermingled —that both are exhib- ited in the mutations of the living substance as well as in the respiratory processes. Thus, on the one hand, assimilation is accompanied not only by endothermic (energy-storing) but also by exothermic (energy-releasing) processes ; while, on the other hand, the partial oxidation of the food proteids may be a necessary step towards assimilation. It is because the net result is the storing or the release of energy that we may speak of any complex of processes as enthodermic or exothermic, and certain foods as plastic or thermogenic. The source of energy in organisms is not, however, solely food. Energy may likewise be derived directly from energy in the environment. This source is of greatest importance in the case of chlorophyllaceous organisms, but it is probably not of importance for them alone. For the heat and light of the environment aid, as we have seen (pp. 166-171, 222-225), various metabolic processes in all kinds of protoplasm. 1. The Materials of which Organisms are Composed.—To determine the sorts of materials which plastic food must supply to the body, it will be instructive to consider the proportional composition of the body out of water and dry substance, both organic and inorganic. Such data, gathered from various animals and plants, are given in the following table : — § 1] UPON THE RATE OF GROWTH 295. TABLE XXV ANIMALS & : a A ay pa) 8.1 Bel 2 #] 3 8] ge] 3 é na SPEOIES. SE 20 oF Leg eee a az | Avrsoriry. =e) 2 8] KE) 2 a] es 3 8 B 3 2 s 6 Fi 3 S$ Al 4 Sponges, average ....] 79.4] 11.0 9.7 54.1 45.9 | Kruxensere, ’80 Meduse : Rhizostoma cuvieri. . .| 95.4 1.6 3.0 34.8 65.2 “ce Actiniaria: Anthea cereus...... 87.6 | 10.7 1.6 87.0 18.0 oe Actinia mesembryanth, | 83.0] 15.4 1.7 90.0 10.0 es Sagartia troglodytes ..| 76.8} 20.9 2.3 81.1 18.9 “ Cerianthus membran. .| 87.7] 11.6 1.7 87.2 12.8 “ Aleyonium palmatum .| 84.3; 10.8 4.9 68.8 31.2 ‘ Asteroidea : Astercanthion glacialis.| 82.3} 14.1 3.6 79.6 20.4 6“ Annelida: Lumbricus complanatus | 87.8 9.7 2.4 80.2 19.8 “ Crustacea : Oniscus murarius. ...| 68.1} 21.2 10.6 66.6 b34 BrEzoxp, °57 Squilla mantis ..... 72.0| 22.1 5.9 78.9 21.1 | Kruxeynene, ’80 Astacus fluviatilus ...| 74.1] 16.8 9.1 64.9 35.1 BEzoxp, °57 Mollusca: Doris tuberculata . . 88.4 9.0 2.6 77.6 22.4 | Kruxenzere, ’80 Doriopsis limbata. . . .| 86.5] 12.4 11 91.9 8.1 6 Arion empiricorum . 86.8) 10.1 3.1 76.5 23.5 BEzoup, '57 Limax maximus 82.1} 16.4 1.5 91.6 8.4 “ Ostrea virginiana. . 88.3] 10.8 0.9 92.3 7.7 (without shell) Tunicata: Botryllus. . 93.6 3.1 3.3 48.4 51.6 | Kruxensere, ’80 Vertebrata: Cyprinus auratus... .|77.8] 17.6 4.6 79.1 20.9 Bezoxp, '57 Triton igneus ...... 80.2} 16.1 3.7 81.1 18.9 ee Triton cristatus..... 79.6 | 17.0 3.4 82.9 17.1 Hie Bombinator igneus .. .| 77.3] 19.4 3.3 85.2 14.8 “ Bufo cinereus...... 79.2) 14.8 6.0 71.1 28.9 te Rana esculenta 82.7 | 14.2 3.0 82.2 17.8 “6 Angius fragilis ..... 55.0] 32.1 12.9 71.5 28.5 ‘“s Lacerta viridis...... 71.4] 23.2 5.4 81.3 18.7 “ Sparrow ......... 67.0] 27.8 5.2 84.3 15.7 “ BAG lacs. Sanat deo: FO es 67.5 | 27.4 5.0 85.2 14.8 7 Mouse) foe ete seas 70.8 | 25.7 8.5 88.0 12.0 “ TOL ig. gee Hee ere ae 65.7 | 29.6 4,7 86.3 18.7. | Vouxmann, "74 296 EFFECT OF CHEMICAL AGENTS [Cu. XI PLANTS Oats, in blossom ... .| 77.0 6.4 16.6 27.8 72.2 Wotrr, '65 Wheat, in blossom . . .| 69.0 9.3 21.7 30.0 70.0 se Pea vines, green ....| 81.5 4.8 13.7 26.0 74.0 o% a. Analysis of the Entire Organism.— We are now ready to consider the atomic composition of the dry substance of organ- isms. VOLKMANN (’74) has contributed data on this subject in the case of man. Thus the dry substance gives :— H N ASH Cc ce) 529% 185% 77% TAG 134% In the case of a plant (stems and leaves of dry clover) we have, according to JOHNSON : — Cc REMAINING ASH 10) H N 58 P AT4% 87.8% 5.0% 21% 0.12% 0.30% 2.0% These two determinations, fairly typical of the higher plants and the higher animals respectively, run nearly parallel. The greatest difference is shown by the nitrogen, which is more than three times as abundant in animals as in plants. Oxygen, on the other hand, is more abundant in plants. The ash, in turn, must be further analyzed. The following table gives the percentage composition of the ash of various organisms : — TABLE XXVI ANIMAL, NeEw-sBorn Dog. MENHADEN (FIsH). Oar Piant. AUTHORITY. Buneg, ’89. Cook, ’68, p. 498. AveNnDT (VINES, ’86, p. 129). CaO 29.5 40.0 12.1 P2O5 39.4 35.8 8.8 K,0 11.4 7.1 45.9 Cl 8.4 3.1 6.1 Na2.O 10.6 4.7 2.82 MgO 1.82 3.1 4.12 Fe203 0.72 — 0.54 SiO, — 6.1 17.2 SOs —_ — 2.86 § 1] UPON THE RATE OF GROWTH 297 It would be valuable to know the relative number of atoms of each of the metalloids and metals named in the preceding table. This may be determined in the following way: Find the proportion by weight of each metallic radical (excluding the oxygen) in the entire ash and divide this percentage by the molecular weight of the metal. The varying weights of the elements are thus eliminated, and a set of numbers which indi- cate relative abundance of atoms is obtained. We multiply these small fractions by 1000 for convenience. The results are as follows :— TABLE XXVII New-norn Doe. MENHADEN (FisH). Oat Prant. Ca 528 715 216 P 555 506 124 K 243 151 974 Cl 24 174 173 Na 343 150 60 Mg 45 17 114 Fe 9 _ 6 Si _ 101 287 iS) — — 86 These examples may suffice to show how diverse is the com- position of different organisms and how diverse therefore must be their requirements in the way of food to build up the adult body. The examples serve also to indicate what are the important elements for organisms. They appear to be the same for animals and plants, and are: — *Carbon *Calcium Sodium *Sulphur *Oxygen *Potassium Chlorine Silicon *Hydrogen *Phosphorus *Magnesium *Iron *Nitrogen While this list does not pretend to exhaust the elements found in organisms, it contains those which are usually present. In the organism the atoms just named are, of course, found in combination. The carbon, oxygen, hydrogen, and nitrogen are contained in the organic matter of the organism — the * Those elements which are starred (*) are essential to all organisms. 298 EFFECT OF CHEMICAL AGENTS [Cu. XI greater part of the entire dry matter. The relations of the remaining elements are largely obscure. Some of them form inorganic acids in the body, such as hydrochloric and sulphuric acids. Others form inorganic compounds deposited in the body as supporting or protective substances, such as the calcic phos- phate and calcic carbonate of bone and spicules and the silicic oxide of plants. But there can be little doubt that a large and highly important part of these elements is built up into organic molecules and in this position plays a weighty and varied part in metabolism and growth. As examples of the way in which the metals and metalloids occur in the organic molecule I may cite a few cases in which the molecular structure has been deter- mined more or less satisfactorily. Thus we have sulphur in albu- men, C7.H1.N4g50..3 iron in hematin, C,,H,,N,FeO,; phos- phorus in lecithin, C,,H,,NPO,, and nuclein, CygHygNyP30o, magnesium in chlorophyllan, and various halogens in the urates of sodium, calcium, and lithium. In discussing as we shall immediately the importance of each of these elements for the formation of the body we shall find additional facts con- cerning the importance of the metallic atoms in the organic molecules. There is good reason for believing that the pecul- iar properties of hemoglobin depend upon its iron and that the characteristic properties of nuclein depend largely upon its. phosphorus and (as the later investigations indicate) its iron also. As our knowledge develops, the importance to many organic molecules in the living body of metallic or metalloid elements becomes clearer; the “ash” of the body is not some- thing accidental, secondary, or superfluous, but is an essential part of the organism. We must now consider the source of the various elements necessary to nutrition. Botanists early determined that C, H, and O enter the organism through the carbonic acid and water which green plants absorb. Concerning the source of nitrogen there has been less certainty ; it is generally believed to come from nitrates in the soil, but that matter will be considered later in more detail. Another source of the more characteris- tically organic elements, C, H, N, and O, is, without doubt, organic compounds of various sorts. Although it has long been known that insectivorous plants absorb the organic mat- § 1] UPON THE RATE OF GROWTH 299 ters they digest, still it is only recently that the fact that green plants in general can make use of organic compounds has been recognized. Bokorny (97) has lately brought together the evidence which makes this conclusion certain. It appears that in the presence of organic solutions some alge may grow for half a year in the absence of carbon dioxide; and the potato plant may, even in the dark, store up starch in its tubers in the presence of rich organic food. Nitrogen may also be gained from amido-bodies ; thus, BASSLER (C87) found that his maize cultures grew better in asparagin, CO,H - CH(NH,) - CH,- CO(NH,), than in potassium nitrate. Thus plants may gain their C, H, O, and N from either organic or inorganic sources. Non-chlorophyllaceous organisms, on the other hand, have long been known to gain their : C, H, N, and O from organic feo compounds ; indeed, it has gen- ° erally been believed that they £ can gain those elements from a b organic compounds only. Cer- tain observations, however, Fre, 84.— a, Nitrosomonas europea (ni- throw doubt upon the entire trite bacteria from Zurich) ; b, Nitro- . “oe. somonas javensis (nitrite bacteria correctness of this belief; these 5... Txvals c Nitrobacter (nitrate are especially the remarkable bacteria from Quito). Magnified 1050. results gained by WINOGRAD- After WinoGRADSKY, from FISCHER, 5 2 ad Vorlesungen tiber Bakterien, 1897. sky (90) from nitrifying bacte- ria (Fig. 84). This author found that the bacteria could grow in a mixture of inorganic salts free of organic matters. Solutions free from organic matter were prepared by the following means: The culture vessels were cleaned by boiling in them sulphuric acid and potassium permanganate. The water used in the cultures and in washing the vessels was twice distilled in vessels without joints of organic material — the second time with the addition of sulphuric acid and potassium permanganate. The magnesium sulphate and potassium phosphate, used as food, were calcined; the calcium carbonate, used in excess, was likewise calcined and saturated with carbon dioxide; finally, the ammonium sul- phate was especially prepared to avoid organic impurities. The culture flasks were plugged with calcined amianthus, not with cotton. ‘The solu- tions were inoculated with a mere trace of the culture containing nitrifying 300 EFFECT OF CHEMICAL AGENTS (Cu. XI organisms. The cultures were then reared either in complete darkness or in dim light. The precautions taken to eliminate organic matters would seem to be complete; but those who know the difficulties of such experi- ments seem willing to admit the possibility “that exceedingly minute quan- tities of organic nitrogen and carbon are actually present” (Jorpan and Ricuarps, ’91, p. 880). On the other hand, “exceedingly minute quanti- ties” of organic matter could hardly account for the vigorous growth of bac- teria; and, in general, a priori objections cannot be permitted to overthrow results gained by the use of methods which are beyond reproach. The organisms placed in this water, deprived of the last traces of organic matter, developed rapidly, but not quite so rapidly as organisms placed in natural water to which the necessary salts had been added. Analysis showed that not only nitrates but also organic carbon compounds had been formed. Thus the careful experiments of WInoGRADsKY demonstrate what the less critical experiments of Heraus (786) had already rendered probable, that a complete synthesis of organic matter may take place through the action of living beings and independently of the solar rays. These noteworthy observa- tions, then, obliterate the last sharp line of distinction between the nutritive processes of chlorophyllaceous and non-chloro- phylaceous organisms. We may now state that the elements C, H, N, and O may be gained from complex organic. food materials by all organisms, and from simple compounds, such as carbonic acids, ammonia, and water, by all chlorophyllaceous organisms, and, very probably, by certain non-chlorophylla- ceous ones also. The elements other than C, H, N, and O are probably gained by chlorophyllaceous and non-chlorophyllaceous organ- isms alike, from either inorganic or organic compounds con- taining the necessary elements; although, possibly, animals make use of the metals more readily when they are in organic compounds. Suitable proportions of the different metals in a nutritive solution for green plants are given in the following tables, showing various standard solutions employed by differ- ent experimenters : — § 1] UPON THE RATE OF GROWTH TABLE XXVIII Nutritive SOLUTIONS FOR PHANEROGAMS Sacus’ Solution Distilled water : Potassium nitrate, KNO; . Calcium sulphate, CaSO, . Magnesium sulphate, MgSO, Calcium phosphate, CaHPO, Ferrous sulphate, FeSO, . Scummper’s Solution oe Distilled water . Gh : Calcium nitrate, Ca(NO,). Potassium nitrate, KNO, . Magnesium sulphate, MgSO, Neutral potassium phosphate, K,PO, Sodium chloride, NaCl bok cs Frawk’s Solution Water, =, distilled; 39 Berlin reservoir water . Calcium nitrate, Ca(NO;). Potassium chloride, KCl . Potassium phosphate, K,;PO, Magnesium sulphate, MgSO, - ae Ferric chloride, Fe,Cl,. : 301 GRAMMES. 1,000.0 1,000,000.0 267.4 121.5 101.9 100.2 trace The first differs from the others chiefly { in the absence of chlo- rine. How fit ordinary waters may be to provide all these salts is shown by this analysis of the ordinary drinking water of Bos- ton (JORDAN and RicHARDS, ’91) :— TABLE XXIX Parts spy Weicut or Inorcanic Matters 1n 1,000,000 Parts oF PoTraBLE WATER Sulphuric acid Chlorine Alumina and owide of iron Calcium oxide . Magnesia Potash Soda . Silica . Nitrates . 4.58 4.00 0.75 6.45 1.60 0.92 5.00 3.04 0.25 302 EFFECT OF CHEMICAL AGENTS [Cu. XL All of the elements mentioned above, except phosphorus, appear in this list. Thus, ordinary drinking water is clearly well adapted to the nutrition of plants. For alge, MouiscH (95) used the solution given in the fol- lowing table : — TABLE XXX Norritive SoLuTion For ALGE GRAMMES. Water 3. Bea Bo ards oS 1,000.0 (NH,).HPO, ae Mey Tey Sern ‘ 0.8 (KH,)PO, . & AOS ae ee el 0.4 MESO). se--4 8 ae ang : 0.4 FeSO, trace (2 drops of a 1%, sol.) Here we note an absence of the calcium used in the solutions for phanerogams. Fungi likewise require a mixture of salts, according to Nace (80, p. 854) and BENECKE (95), in the following proportions : — TABLE XXXI Nutritive So.utions ror Funer NA&cELI’s Solution Bevecke’s Solution GRAMMES. GRAMMES. Water 1,000.0 | Water 1,000.0 (NH,)H.PO, Gay 0.5 | KH,PO,. . bu 5.0 MgS80,+7H,O .. . 0.5 | MgSO,+7H,0 . 0.01 KCl, bite & aes 0.5 | K,SO, . . .. ‘ 0.5 FeSO, 0.05 | NH,Cl . 10.0 Organic Compounds FeSO, trace Glycerine . 50.0 The solutions differ principally in the proportion of the salts. Finally, all animals likewise require a certain quantity of salts. What the proportions are can be shown in the case of, young mammals, which live during part of their growing period exclusively upon milk. A wonderfully close relation exists, indeed, between the proportions of the mineral con- stituents of milk and of the young mammal before it has begun to suck. This is shown in the analyses made by BUNGE (’89) upon the milk of a dog and the body of its newly-born pup. § 1] UPON THE RATE OF GROWTH 803 TABLE XXXII Comparison oF Aso In New-Born Doc anv 1n THE MILK oF ITs MoTHER Aga In MILK: In New-sorn Doe: % or ASH. % oF ASH. P.Os 34.2 39.4 CaO 27.2 20.6 Cl 16.9 8.4 K,0 15.0 11.4 Na,O 8.8 10.6 MgO 1.5 1.4 Fe203 0.12 0.72 The quantities in the two columns are fairly similar. The greatest proportional difference occurs in the case of tron, and this fact requires a special explanation, which is briefly this, that iron is more important for the rapidly growing embryonic stages than for later life. So likewise in the eggs of birds we find stored up all the mineral matters which are necessary for their development. Thus the yoke of the hen’s egg contains phosphoric acid, lime, chlorine, potassa, soda, magnesia, iron oxide, and silica in the relative abundance indicated in this descending series. This series closely agrees with that given for milk. In the case of marine animals, also, certain inorganic elements are a necessary food. The following list of such elements is. based upon the results of thorough experiments by HERBST C97) upon developing eggs of sea-urchins, starfishes, hydroids, ctenophores, and tunicates ; the most favorable proportions of the elements were not, however, determined: calcium (in the form of carbonate, sulphate, or chloride), chlorine, iron (trace), magnesium, phosphorus (as Ca,P,0, or CaHPQO,), potassium, sodium, and sulphur. Now all these elements are found in sea water, which in the Mediterranean Sea near Naples contains in 1000 parts of water * * After ForcHHAMMER (’61), p. 383. 804 EFFECT OF CHEMICAL AGENTS (Cu. XI 30.292 parts NaCl 3.240 “ MgCl, 2.638 “ MgSO, 1.605 “ CaSO, 0.779 “ KCl 0.080 “ silicic acid, calcium phosphate, and insolu- Total . 38.634 ble residue, including CaCO, and Fe,O3. From the foregoing tables it appears that mineral substances, and essentially the same mineral substances, are required by all organisms. The differences in this respect between the different organisms are slight. Thus while sodium is not included among the necessary elements of either chlorophyl- laceous plants or fungi, its occurrence in considerable quantity in milk, probably associated with chlorine as common salt, indi- cates that it is important for some animals. The important conclusion seems warranted that all organisms may use as hylogenic food any sort of compound which will furnish the appropriate elements, but that among animals, and to a less degree among fungi, organic combinations have the preference because they fulfil at the same time the thermogenic function. 6. Detailed Account of the Various Elements used as Food. — We may now consider the part which each element plays in the growth of the body as a whole, reserving for the Fourth Part a consideration of the specific réle which the element plays in organs of the body. We may, in general, consider first the share taken by the element in the constitution of the body, then the form in which the element gains access to the body, and finally what general effect it has upon the growth of the organism. Oxygen.— Excepting carbon, oxygen constitutes a greater part of the body, by weight, than any other element. Between 20% and 25% of the dry substance of the human body and between 85% and 45% of that of green plants is oxygen. The oxygen used as hylogenic food comes to land-animals from the organic compounds and the air consumed by the developing young; the oxygen of water-animals may come from their food or from the oxygen dissolved in water ; finally, §1) UPON THE RATE OF GROWTH 305 that of phanerogams is believed to be gained chiefly from the air at all parts of the body, roots as well as stems and leaves. Since oxygen is of great importance for metabolism (p. 2), it is naturally essential to growth. It is well known that the lower the oxygen tension is, the more slowly do seeds germinate and pass through their early stages of growth. Thus in an experiment performed by Bert (’78, pp. 848-858) barley grains which germinated and were reared at various pressures had in six days the following dry weights : — ATMOSPHERIC PRESSURE. REsuLtTING WEIGHT. 76 cm. mercury (normal atmosphere) 8.8 mg. 50 “ (0.66 - ) 71 25 “ (0.33 >) 6.2 7 ub (0.1 a ) No growth On the contrary, as the oxygen pressure increases up to about twice the normal, growth is accelerated, but beyond that point growth is retarded until at about 7 atmospheres growth hardly occurs. In older seedlings, observations upon which have been made by WIELER (’83), JENTYS (88), and JACCARD (93), atmos- pheric pressure below the normal, even down to one-fourth or one-eighth of the normal, appears to induce accelerated growth ; likewise in pure oxygen at the atmospheric pressure growth is as rapid as or somewhat more rapid than in the ordinary at- mosphere. When, however, the oxygen tension is above the atmospheric pressure or below one-eighth of the normal, growth is retarded. It thus appears that an abnormal oxygen pressure may accelerate growth, and as we shall see later, the same effect is produced by other abnormal conditions. Among animals, also, the oxygen tension exerts an important effect upon growth. This is shown by the experiments of RavsBer (84, pp. 57-65) upon the eggs of the frog. To get a variable atmospheric pressure RAUBER used champagne flasks in which were put the eggs and a little water. Through the air-tight cork of the inverted flask one end of a U-shaped glass tube of proper length and strength was passed. To the other end was fixed a funnel through which x 306 EFFECT OF CHEMICAL AGENTS [Cu. XI mercury could be poured into the tube. The column of mercury produced the increased pressure in the flask, and the difference in height of the mercury in the two arms of the tube was a measure of this pressure. To get a pressure below the normal a partial vacuum was produced by a water- pump and the flask was then sealed. We assume (with Brrr, ’78, p. 1153) that the chief effect of the variation in the atmospheric pressure was the variation in the amount of oxygen absorbed by the water. Pure oxygen was also used in the flask. At a pressure of three atmospheres no growth occurred. At a pressure of two atmospheres growth was slower than at the normal pressure. At three-fourths of an atmosphere also growth was retarded and at one-half an atmosphere death generally occurred. Thus the optimum condition of oxygen tension is near the normal for the atmosphere. The same thing is indicated in a qualitative way by the experiments of Lorn (92). The stems of the hydroid Tubu- laria possess in ordinary water a high regenerative capacity, but in water deprived of oxygen by boiling no regeneration takes place, although, after the water has been aerated again by shaking, rapid growth occurs. Hydrogen.—This element forms, in its various compounds, between 5% and 10%, by weight, of the dry substance of organisms. How is it acquired? In the case of plants it is believed that it is taken into the organism as a constituent of water, which combines with carbon or carbonic acid in the plant, forming either starch directly or some other compound from which starch is later derived. Other possible sources of hydrogen are ammonia and its compounds, also the organic compounds absorbed. The hydrogen of fungi and animals has clearly been derived from the latter compounds alone. The effect of hydrogen gas upon growth seems to be merely that due to the replacement of oxygen; it has no active effect. Carbon is the largest constituent of dry organic matter, of which it forms between about 44% and 60%. In green plants it is obtained for the most part from the carbon dioxide or carbonic acid of the air which is absorbed by the leaves. Other sources of carbon for green plants are found in many organic compounds, such as urea, uric acid, hippurie acid, glycocoll, kreatin, guanin, asparagin, lucin, tyrosin, and acetamid. These afford nitrogen also. Certain green plants make use of animal §1) UPON THE RATE OF GROWTH 307 matter, e.g. insects, as food. Fungi and animals obtain their earbon from carbon compounds elaborated by plants. The indispensableness of carbon for the life of all organisms as well as for their growth requires no illustration. Nitrogen. — Of the importance of nitrogen as a hylogenic food nothing more need be said than that it is essential to the formation of albumen. The ordinary form in which nitrogen is Fic. 85.— Cultures of Sinapis alba in pure quartz sand, to which have been added equal amounts of a nutritive solution, but unequal quantities of nitrogen in the form of calcic nitrate, as follows: A, without nitrogen; B, 0.1 gramme calcic nitrate in each vessel; C, 0.6 gramme calcic nitrate in each vessel. After a photo- graph. From Frank (’92). obtained by the seedling is, as already stated (p. 298), that of the nitrates or ammonia in the soil (Fig. 85). Growing fungi gain it chiefly from nitrogenous organic compounds, but many fungi can make use of ammonium nitrate for this purpose. Growing animals gain nitrogen chiefly, if not exclusively, from organic compounds, especially albumen and allied substances. Free nitrogen is found wide-spread in nature. It forms about 79% of the volume of the air; penetrates into water, though in a smaller proportion than in the air, and even into the soil. Thus for organisms living in any of these media free 308 EFFECT OF CHEMICAL AGENTS (Cu. XI nitrogen is a possible food. Is it actually made use of? This question has until recently usually been answered in the nega- tive, and this conclusion was the more readily accepted since nitrogen is a notoriously inert gas. Another view, however, has within recent years come to obtain. It developed in this wise. It had long been known that land which has lain fallow or on which clover or other leguminous crops have been reared is in a way strengthened as if fertilized, and it was also known that this strengthening is due to the fact that the soil acquires nitrogen from the air and “fixes” it in the form of nitrates. While the studies of PasTEuR on fermentation, since 1862, had paved the way for the interpretation of the process, the fact that it is due to organ- isms was first proved by ScHLOSING and Mintz (77, ’79). This proof they made by chloroforming a certain mass of nitri- fying earth and finding that the nitrifying process thereupon ceased. Later, they isolated a form of bacteria which had the nitrifying property. Their results were quickly confirmed and extended by others, notably BERTHELOT (85, ’92, etc.), in a long series of investigations, so that there is now no question that the nitrification of the earth is brought about by the activity of bacteria, perhaps of several species. The results thus gained were extended to some of the higher fungi by FRANK (92, p. 596). Spores of Penicillium cladosporioides were sown in a nutritive solution of pure grape sugar and mineral salts, completely free of nitrogen, and in the presence of air which had been freed from ammonia by passing through sulphuric acid. The fungi grew, but not so rapidly as those in a solution containing nitrogenous compounds, and produced a mass of hyphe. These hyphz, when tested, yielded ammonia. One such culture solution of 65 ce. volume became filled with the fungus mass in ten months and yielded 0.0035 gramme of nitrogen, which must have been derived from the air. As similar results have been gained for other molds by BERTHELOT (93) and for Aspergillus and Penicillium glau- cum by PuURIEWITSCH (95), we seem almost justified in pre- dicting that the capacity for assimilating free, atmospheric nitrogen will prove to be a characteristic of all fungi. Now if it is conceded that some organisms can make use of the nitrogen of the air, it is clear that the a priori objection to §1j UPON THE RATE OF GROWTH 309 all organisms doing so, the objection, that is, on the ground of the inertness of nitrogen, is disposed of. The question is now merely one of fact. Do the alge, the higher plants, and the animals make nitrogenous compounds out of free atmospheric nitrogen? Of these groups, the alge first claim our attention because of the inherent probability that they will act more like bacteria than any other group, since they pass over into the bacteria through such connecting forms as the Oscillariz and Nostocs. ScHLUsING and LAURENT (’92), FRANK (93), KocH and KossowlITScH (93), experimented with various species of Nos- toc, Oscillaria, Lyngbya, Tetraspora, Protococcus, Pleurococ- cus, Cystococcus, Ulothrix, etc., and found that, when supplied with a non-nitrogenous food, these plants produced nitrogenous compounds in the substratum, evidently gaining their nitrogen from the previously purified air. Doubt exists, however, as to whether the free nitrogen is taken in directly by the alge or only after having been assimi- lated by bacteria associated with the alge and by them made into nitrogenous compounds. For the latter alternative speak the experiments of KossowitscH (’94) and Mo.uiscH (95). Kossow!tscH, who with Koc had previously found that alge gain nitrogen from the air when reared in impure cultures, now took special pains to get algal cultures free from bacteria. To this end he reared alge on potassium silicate permeated by a nutritive solution. The pure cultures thus gained were then grown in a sterilized flask to which air, freed from ammonia, was admitted. The nutritive solution was made of salts free from nitrogen but containing the other essential elements. The results of this experiment were striking. The pure cult- ures of alge grew for a time, but then ceased. New non- nitrogenous food did not revive them, but the addition of nitrates caused rapid growth. Other evidence was gained from analyses. When the cult- ures of alge were pure there was no increase in the amount of nitrogen in the dry matter of the alge. But when bacteria were mingled with the alge, the quantity of nitrogen was increased. This is shown in the following typical analy- sis: — 310 EFFECT OF CHEMICAL AGENTS (Cu. XI MILLIGRAMMES OF N IN CULTURE. CoNnTENTS OF CULTURE. AT THE BEGINNING. AT THE END. Cystococcus, pure culture 2.6 2.7 P a, f no sugar 2.6 3.1 Cystococcus, with bacteria with aes 26 81 These results, abundantly confirmed by MouiscH (’95), seem to show that unless bacteria are present alge can build up free N into nitrogenous compounds only slowly, if at all.* While ScHL6sinG and Mintz, BERTHELOT, and others were gaining an explanation of the enrichment of fallow ground, HELLRIEGEL (’86) and WILFARTH were making their investi- gations upon the cause of the enriching action of leguminous crops, which led them to the conclusion that it was due to the fixation of nitrogen in plants with root-nodosities containing bacteria, the compounds thus formed by the symbiotic bacteria being directly assimilated by the plant. This conclusion has been repeatedly sustained for leguminous plants (Fig. 86). The question whether green phanerogamous plants other than legumes can make use of free atmospheric nitrogen is one which is still in hot debate, and it is not an easy one to answer. The calm conviction, based chiefly upon the excellent work of BoussInGAvuLT (60), and Lawes, GILBERT, and PucH (’61), that nitrogen is not thus obtained was rudely shaken by the paper of FRANK (’93) in which that author stated that he finds that nitrogen is removed from the air by non-leguminous plants— plants, moreover, which are not known to have bacteria living in their roots. Consequently he is of opinion that perhaps the fixation of free nitrogen may be carried on by any living plant cell. The difficulties in the solution of the problem may thus be set forth. It is recognized that all growing plants make use * One ‘‘crucial test’? of Franx still requires an explanation. If the free nitrogen is ‘‘ fixed” by the aid of bacteria, the process should go on in the dark. Experiment shows that it does not do so. This difficulty Kossow1tscu over- comes by the assumption that the activities of the bacteria are dependent upon certain carbohydrates which the plant can afford them only in the light. § 1) UPON THE RATE OF GROWTH 31L of nitrogen, but the nitrogen is usually obtained from the soil in the form of nitrates. It is feasible to determine by analysis the amount of nitrogen in the soil at the beginning of the ex- periment and the amount in the seed planted, and then after the experiment to determine the quantity in the soil and in the plant. But the difficulty comes in interpreting the results Fic. 86. — Parallel cultures of peas in the symbiotic and the non-symbiotic conditions. Each series comprises three culture vessels: 8, the symbiotic plants in soil with- out nitrogen; C, the non-symbiotic plants in like soil; A, for comparison, non- symbiotic plants after addition of nitrate to the soil. After a photograph. (From FRANK, ’92.) of the analyses. Thus the fact that the sum of nitrogen in the plant and the soil is greater at the end than at the beginning of the experiment does not prove that the plant has taken in free nitrogen ; for, as we have seen, the soil contains nitrifying bacteria, which intermediate between the free nitrogen of the air and the nitrates absorbed by the green plants. This diffi- 312 EFFECT OF CHEMICAL AGENTS (Cu. XI culty may be partly met by sterilizing the soil, but this prob- ably produces also other changes than the death of the bacteria. The most careful observations of the last five years have not supported FRANK’s generalization. Here and there there have been observers who, like LIEBsCHER (’92) and STOKLASA (96), believe they have evidence for the direct assimilation of free nitrogen by the cells of phanerogams. But the evidence for the contrary opinion is predominant. The experiments which speak for the theory that green plants cannot directly make use of free nitrogen are not in unison. Thus, some indicate that in non-leguminous as well as leguminous plants nitrogen of the air is indirectly made use of through the action of the bacteria of the soil, while accord- ing to others it would seem not to be made use of at all. To the first class belong the experiments of PETERMaNN (91, ’92, and ’93) with barley, of Nopse and HILTNER (795) with mustard, oats, and buckwheat, and of PFEIFFER and FRANKE (96) with mustard. To the second class belong the experi- ments of ScHLosinc and LAuRENT (’92 and ’92*) with various plants, Day (94) with barley, and ArBy (’96) with mustard. In the second class, however, the experimental con- ditions did not favor the development of the bacteria of the soil. The experiments of PETERMANN were, however, carried out upon a very large scale and. under practically normal con- ditions and showed a marked difference between the acquisi- tion of nitrogen by barley growing in an unsterilized soil and in a sterilized one. Likewise NoBBE and HILTNER, and PFEIFFER and FRANKE, were careful to rear plants under normal conditions, so that their results are worthy of especial consideration. They agree that there is an acquisition of nitrogen by the plant growing in normal soil and that this occurs only when the soil is unsterilized. We conclude then that probably phanerogams, like alge, can use the free nitro- gen of the air as food only after it has been converted into nitrates by the action of the nitrifying organisms — the bac- teria of the soil. Turning now to animals, whose nutrition is often compared with that of fungi, we find an absence of knowledge on the subject of the nutritiveness of free nitrogen. It is clear that §1) UPON THE RATE OF GROWTH 313 land animals are in a favorable position for making use of it, since it penetrates with the oxygen to all parts of the body. It is found in the blood of mammals, but still as free nitrogen. Whether it eventually becomes fixed in the body is entirely unknown. The a priori argument against such fixation — the argument of. inertness — has lost much of its force since the discovery of the nitrifying organisms. Phosphorus. —This element is of constant occurrence in organisms. It has been found in yeast, mucors of the most diverse kinds, seeds, plant tissues, and animal tissues of all kinds. It is indeed one of the first among the mineral ele- ments of most organisms, as shown on pages 296 and 297. Of the dry substance of a fish, about 7% is phosphoric acid, and the dry substance of many seeds yields 15%. Phosphorus occurs in organisms as phosphoric acid compounds. Of these the most important organic compounds are nuclein, which has albuminoid properties, and occurs chiefly in all nuclei and in deutoplasm; lecithin, of a fatty nature, occurring in yeast, plasmodium of AXéthalium, seeds, milk, yolk of eggs, and nervous tissue; and glycerin-phosphorie acid, a product of decomposition of lecithin and found wherever the latter occurs. As examples of inorganic salts we have the sodium and potas- sium phosphates of the blood and tissues and the calcium phos- phate deposited in bone. So important an element as phosphorus would naturally form an essential part of the food of all growing organisms. It is supplied at first in the germ,—seed or egg, — but later must come from without. Plants gain phosphorus from the disinte- grating rocks. Animals derive it chiefly from plants, directly or indirectly, or from the calcic phosphate of the sea; in mam- mals it is supplied to the developing young through the milk, which, as we have seen on page 303, is rich in phosphates. The abundance of phosphorus in the body indicates that its office in the organism is an important one, and its peculiar abundance in seeds, yolk, and milk indicates that it is especially important in growth. Experiments have been directed towards this point. The fact has long been established that plant growth cannot occur in the absence of phosphates, and this is true not only for green plants, but also for molds and yeast 314 EFFECT OF CHEMICAL AGENTS (Cu. XT (Raviry, °69). Embryos of various marine animals also will not develop in the absence of phosphorus (HERBST, 97). The peculiar importance of phosphorus for growth is also indicated by the fact that Hartia and WEBER (’88) found more phos- phoric acid in the ash of the growing ends of the plant than in its fully differentiated parts. Again, Lozw (91*) found that Spirogyra kept in a nutritive solution of salts in which phos- phorus alone was lacking, continued to live and, indeed, to form starch and albumen, but its cells did not grow or divide ; so that Lorw concludes that an important use of phosphorus is to nourish the cell-nucleus, and this fact is easily understood from the known importance of the phosphorus-containing nuclein of chromatin in cell-division. All these facts go to show that phosphorus is of prime importance in the growth of organisms. Arsenic, Antimony, Boron, and Bismuth, and their compounds, are apparently all injurious to organisms, so that sublethal solutions strong enough to be active, interfere with or even inhibit growth. Sulphur.— This element is, without doubt, of constant oc-: currence in organisms of all sorts, for it constitutes between 0.3% and 2% of all proteids, out of which organic bodies are largely composed. Sulphur forms between 0.6% and 1% of various (dry) organs of man, and nearly 1% of the dry sub- stance of a month-old seedling of Sinapis alba. In the growth of a plant (Sinapis alba) the amount of its. sulphur increases from 0.02 mg. in the seed to 84.4 mg. in the adult plant, and, indeed, it has been shown in one case (ARENDT, 59, for the oat plant) that the percentage of sul- phuric acid in the ash increases from 2.9 to 4.2 as the plant develops from a seedling to maturity. Since the sulphur goes. chiefly into the composition of the living substance, its hylo- genic importance for growth is evident. The form in which sulphur may be taken into the body is very varied. It is well known that green plants usually absorb it in the form of sulphates, especially sulphates of potassium, calcium, and magnesium; marine animals take it chiefly from the calcic sulphate of sea water, and land animals. gain it largely from organic sulphur compounds produced in. § 1) UPON THE RATE OF GROWTH 815 plants. Whether non-chlorophyllaceous plants can make use of it has been much discussed, and is worthy of further inves- tigation. WINOGRADSKY (’88, ’89) has, indeed, shown that the sulpho-bacteria store up pure sulphur from sulphuretted hydrogen (H,S), and Prescw (’90) has concluded, as a result of feeding himself with pure sulphur and analyzing the sulphur of the urine, that about one-fourth of the sulphur taken into the body in an elementary form becomes built up into organic molecules. Recently Herbst (97) has shown that embryos Fic. 87.— Right, Larva of Echinus reared for 72 hours in water containing all the necessary salts; the sulphur being in the form of 0.26% magnesium sulphate and 0.1% calcic sulphate, and the phosphate in the form of CaHPO,. The larva is normal. Left, Larva reared for 68 hours in a solution containing no sulphur nor CaClz. The typical larva without sulphur, but with CaCly, differs from this chiefly in the presence of rudimentary spicules; kr, spicule-forming cells. (From HErRgst, 97.) of sea-urchins and other marine animals do not develop in the absence of sulphur (Fig. 87). These facts indicate that not green plants merely, but all organisms, can use elementary sulphur as a hylogenic food. The Halogens, chlorine, bromine, iodine, and fluorine, are elements which are closely similar in their chemical reactions 316 EFFECT OF CHEMICAL AGENTS (Cu. XI outside of organisms, and carry a part of that peculiarity with them into organisms. All of them are of physiological interest ; but so far as we know chlorine and iodine are most important. Chlorine. — This element is probably of constant occurrence in organisms, and indeed in rather large quantities, as Table XXVII, p. 297, shows. It is not strange that it should be so, since this element is very widely distributed in all waters. This very fact, however, renders it possible that chlorine is merely an accidental constituent of organisms, being unessential to growth, and precisely this conclusion has been maintained. Of green plants it was early asserted that growth occurs as readily in solutions containing no chlorine as in ordinary potable water, but of late years evidence opposed to this view has been accumulating. Thus, while it appears that growth may occur in the absence of chlorine, ASCHOFF (90) and others have found that growth is not so vigorous as in solutions containing this element. It has been thought that chlorine makes an advantageous combination with the potassium neces- sary for the plant, but the true significance of the favorable properties of chlorine remains undetermined. Turning to animals, we find that chlorine occurs in the milk of mammals, and is therefore probably necessary to them. According to HERBST (’97, p. 709) it is a necessary food for young echinoids. Certainly in the form of sodium chloride it is an essential food of the higher animals, and some of them, especially the herbivora, require large quantities of it, as “salt- licks” testify. The function of chlorine is not altogether plain. It must be used in the production of the hydrochloric acid of the digestive juices. In addition, sodium chloride is found widely distributed in the tissues. It has often been asserted that it goes through the tissues unchanged; but NEwNcxI and ScHoUMOW-SIMANOWSKY (’94) believe that it is probably disintegrated and the chlorine built up into organic molecules. Bromine. — The normal occurrence of traces of this element has lately been demonstrated by Hortrrer (90) for a great variety of plants. It occurs most abundantly in various fruits, apple, pear, peach, and also in the leaves and twigs of many plants, as well as in various berries. Its normal occur- § 1] UPON THE RATE OF GROWTH 317 rence permits us to believe that it has an importance, if not for growth, at least for development; there is, however, no direct evidence that it is generally necessary to organisms. Since it is closely allied to chlorine, the question whether it may replace chlorine in growth has been tested. NENCKI and ScHoUMOW- SIMANOWSKY (94) have found that in the higher animals the bromides can replace the chlorides to a limited extent, but are clearly less advantageous. Altogether the importance of bromine for growth is slight. Iodine. — This element is of wide-spread occurrence in organ- isms, probably as a constituent of organic molecules, for it is found in plants, especially in some species of Fucus and Lami- naria (cf. ESCHLE, ’97); in invertebrates, especially in sponges and the stem of Gorgonia; and in vertebrates, especially in mammals, where it has recently been shown to be most im- portant for growth. It has long been known that mammals which have been deprived of the thyroid gland acquire a weak condition of body known as myxcedema. This effect has been accounted for by the loss, to the organism, of a substance elaborated in the thyroid gland; for when the thyroid gland, or a docoction of it, is fed to the animal it recovers to a certain extent its normal condition. The nature of this substance has been investigated by BAUMANN and Roos (96), who find that it is a compound of iodine —thyroiodine; for when thyro- iodine is fed to the myxedema patient, the same favorable result ensues as follows feeding upon the gland. Fluorine is found rather widely distributed among verte- brates in very minute quantities. It forms about 1.3% of the total ash of bone. It is present also in the hen’s egg, being more abundant in the yolk than in the albumen (TAMMANN, °88). Since it is chiefly found in the body as a constituent of bone, possibly in the form of the mineral apatite, Ca,)F, (PO,),, it may very well be that its chief importance is in the consti- tution of this formed substance. According to BRANDL and TAPPEINER (92) the normal amount in the body may be greatly increased by feeding small quantities of sodium fluoride during a long period. Altogether, we have no reason for thinking that fluorine is essential to the growth of organisms in general. 318 EFFECT OF CHEMICAL AGENTS (Cu. XI Salts of Alkalis.— This group contains one or two of the most important elements of which organisms are composed. The elements are only slightly replaceable by one another. Lithium seems normally to have little importance for growth, although slight traces of it have been found spectroscopically in the blood (HoprE-SEYLER, ’81, p. 453). Sodium is probably of constant occurrence in organisms. The quantity of it in the body is widely different in different species; and as our table on page 297 shows, it may vary in its position from one of the most abundant of the elements to one of the least. Whereas sodium is not essential to the nutrition of plants, it is necessary in the form of sodium chloride to certain higher animals. Sodium is also found in all the tissues of the body, and perhaps enters into the albuminoid molecule (NeEncxi, 94). The fact that, as we have seen on page 308, soda is a prominent constituent of milk, indicates its impor- tance in the growth of mammals. Finally, HERgsr (’97) has been able to demonstrate its indispensability for the growth of marine animals. Potassium constitutes an important part of all organisms. It forms the largest part of the ash of nearly all phanerogams (see page 297) and is markedly abundant in yeast and in many invertebrates. It occurs in the body as chloride and as sul- phate, and probably also in combination with albumen and various organic acids (VINES, p. 134). That it is an essential and unreplaceable food for all organ- isms is indicated by trustworthy experiments upon fungi, alge, phanerogams, invertebrates, and vertebrates. RAULIN (769) first showed that only culture-solutions containing this metal permit the growth of fungi. The experiments of BENEOKE (96) upon the growth of certain molds, e.g. Aspergillus, are worth citing in detail as an illustration of the method. He sowed spores in culture-vessels made of a glass which analysis had shown to be free from potassium. Two of these vessels contained a nutri- tive aqueous solution consisting of 38% cane sugar and 0.25% magnesium sulphate. To the one of these solutions was added 1.2% potassium nitrate, and 0.26% potassium phosphate; and to the other 1% sodium nitrate and 0.5% sodium phosphate. After four days the first culture was covered by a sheet of fungi and in five weeks the whole surface was black with spores; in § 1] UPON THE RATE OF GROWTH 319 the second culture, on the other hand, little growth had occurred even at the end of five weeks. The crop from each of the cultures was then harvested and its dry weight determined. That of the first culture was 0.3 gramme, that of the second 0.03 gramme. By a somewhat similar procedure MouiscH (95) has been able to show that potassium is essential to the growth of alge ; and NosBeE and others (’71) that it is necessary for the growth of phanerogams. The experiments upon animals have been rather less satisfac- tory on account of the greater difficulties in experimentation. Fic. 88. —Two embryos of Spherechinus from parallel cultures. wu, reared ina solu- tion containing all the necessary salts; embryo normal. b, reared in the same solution, but without potassium ; blastula wall abnormally dense, and embryo of small size. (From HErsst, ’97.) Nevertheless we have some trustworthy data upon this matter. On the side of the invertebrates we have the experiments of Lors (’92), who placed a hydroid, Tubularia, in fresh water to which solutions of various combinations of the salts found in sea water were added so as to give approximately the nor- mal osmotic effect. Under these circumstances regeneration of the hydroids occurred only in the solutions containing potassium. Again, Herpst (’97) finds potassium essential to the growth of embryos of echinoids (Fig. 88). Thus the potassium compounds seem necessary to the processes upon which growth depends. On the side of vertebrates we have the somewhat inconclusive results of KEMMERICH (69), who fed two young dogs of the same age and of nearly the same size upon meat boiled until a large portion of its salts was extracted. To the food of one dog he added only sodium chlo- 820 EFFECT OF CHEMICAL AGENTS (Cu. XT ride; to that of the other, both sodium chloride and potassium salts. After 26 days the dog fed on the potassium salts as well as the sodium chloride was about 30% heavier than the other, and this difference was reasonably ascribed to the beneficial effects of the potassium. The particular part which potassium takes in growth is still somewhat doubtful. The recent observations of COPELAND C9T) with seedlings reared in water cultures in which sodium replaces potassium, lead him to the conclusion that potassium is necessary to turgescence. The potassium salts become lodged in the cell-sap, as analysis shows, and are therefore, perhaps, one of the principal causes of imbibition. Rubidium and Cesium. — These rather rare metals are important only because of the fact that they may replace potassium in the growth of some fungi. WunoGrapsky (’84) recognized this to be the case with rubidium in yeast cultures. NAGELI (780) found that in molds rubidium and cesium gave even greater growth of dry substance than potassium cultures, a conclusion abundantly confirmed by the studies of BENECKE (95). Whatever, therefore, is the significance of potassium for growth, rubidium and cesium seem to have the same significance. Earthy Metals. — Under this head are included the elements calcium, strontium, and barium, which form compounds having closely similar molecular structure and properties. We might therefore expect them to be in some degree mutually replace- able. Caletum shares with potassium and phosphorus the position of one of the most abundant elements of organisms. It is found in every tissue and seems to be a constant accompaniment of protoplasm. Its constant occurrence is indicative of its importance as food for both plants and animals. It is apparently indispensa- ble and unreplaceable by any other element in phanerogams ; but Moniscu (94+) finds that growth can take place in certain molds (Penicillium, Aspergillus) as well in its absence as in its presence, and in some alge, but not in all (Moniscu, ’95), calcium is apparently of little importance. In animals, calcium can be replaced by other elements only to a very slight extent. § 1) UPON THE RATE OF GROWTH 321 Its absence from the water in which echinoid larve are developing produces dwarfs. In vertebrates, owing to the need of this metal for the skeleton, large quantities of calcium are taken in by the growing organism. In normal growth, then, the food of animals and phanerogams must contain calcium. Strontium, although closely allied to calcium, is rather rarely found in considerable amount in organisms. In certain plants, as e.g. Fucus, it is constantly present. It can be stored up in the animal organism when supplied abundantly in the food, but in general is believed to be of little importance for growth. Manganese, likewise, is not of general importance, although it is found abundantly in certain plants, e.g. Trapa natans, Quercus robur, and Castanea vesca, and in the excretory organ of the mollusc Pinna squamosa (KRUKENBERG, ’78). Iron. — This most abundant of the heavy metals occurs so frequently in organic substances, especially those related to the compounds found in protoplasm, that it is little wonder that iron has been found to be an essential ingredient of all proto- plasm, hardly less important than oxygen itself. Although its occurrence has been demonstrated, especially by SCHNEIDER (89), in all the large groups of animals, its amount in any individual or organ is always very small. Iron oxide (Fe,O,) forms between 1% and 2% of the ash of muscle, about 5% of the ash of blood, and rarely rises to 5% in plants. It is found in the body, for the most part, as in yolk (BunGE, ’85), in organic union. It occurs thus in the chro- matin of the nucleus of all cells (MAcALLUM, ’92, °94; SCHNEIDER, 795). That chromatin contains iron has been demonstrated by MacaLtum (91) by means of a microchemical method whose general validity has never, so far as I know, been questioned. It was shown by Buneg, in 1885, that when tissue is put into ammonium sulphide the iron, even in an organic molecule, is separated from its compound, and uniting with the sulphur forms ferrous sulphide (FeS). This ferrous sulphide appears in the proto- plasm as green granules (black in large quantity); and the fact that these granules appear abundantly in the nucleus shows that iron is especially abundant there. Additional evidence is given if after several weeks the chromatin loses its stained appearance and becomes rusty. This result is interpreted as due to the formation of ferric oxide, Fe,O,; for when the x 322 EFFECT OF CHEMICAL AGENTS (Cu. XI nuclei are subjected to hydrochloric acid and potassium ferricyanide they immediately assume a deep azure-blue color, clearly due to the formation of “Prussian blue” or Fe,(FeC,N,)3 This series of reactions can only be explained on the ground that there is iron in the nucleus. Iron has shown itself to be essential to the growth of all organisms. Its importance for growth is indicated by its rela- tive abundance in the yolk of birds’ eggs, and by the fact of. its occurrence in larger proportion in a mammal just born than Fic. 89. —Echinus larve from parallel cultures, all 5} days old. a, reared in a solu- tion containing all salts, including iron as FeCls; 6 and c, from solutions contain- ing all salts excepting iron. (From HERBST, ’97.) in later stages. When excluded from a nutritive solution which is otherwise complete, growth is imperfect (Fig. 89). This may be associated with the facts that in plants the chloro- phyll granules are not developed in its absence, that in the higher animals hemoglobin cannot be formed, and that the chromatic substance of all cells requires it. The question in what form iron is absorbed by the organism has been the subject of an extensive discussion. Although doses of metallic iron have long been used with favorable §1] UPON THE RATE OF GROWTH 323 results in medical practice, BuNGE (785) concluded that only organic iron compounds are assimilable. The studies of KUNKEL (’91 and ’95) and WoLTERING (95) have, however, shown in the clearest manner that inorganic iron is assimilated, stored in the liver, and made use of in the construction of such organic compounds as the hemoglobin of the blood. At the same time, as Socin (91) and others have shown, iron may be gained from organic compounds. Apparently, iron com- pounds of any sort may be made use of by the organism. Magnesium. —This metal is closely associated with calcium, the two usually occurring together in organisms just as they do in the inorganic world. As the table on page 297 shows, magnesium is of constant occurrence among organisms, although never present in great quantity. The magnesium is gained by green plants at the same time with the calcium from mineral salts (chiefly magnesium carbonate and sulphate) derived from disintegrating rocks. Fungi can also make direct use of the salts of magnesium (excepting always the chloride) ; and ani- mals, although no doubt chiefly gaining their magnesium from plants or the waters in which they live, may make use of min- eral salts, especially in the construction of the mineral parts of various formed substances, such as those of bone. So constant an element is presumably necessary to the organ- ism, and numerous observations make it quite certain that this is true for green plants in general. Indeed, the fact that mag- nesium occurs in chlorophyllan of chlorophyll makes it prob- able that it functions in assimilation. Concerning its indis- pensableness for fungi there can likewise be no doubt, since BENECKE’s (’95, p. 519) experiments show it to be replaceable neither by calcium, barium, or strontium. While some investi- gators, like Hoppr-SEYLER, believed it to have little signifi- cance for the animal body, —to be an accidental accompaniment of calcium,—later study has shown that it is of importance for regeneration of hydroids (LOEB, °92), and, according to HERBST (97), a constituent of the sea water which is necessary to the normal growth of various marine larve. Also its occur- rence, although slight, in milk, as well as its very abundant occurrence in seeds, indicate that it plays an important, if an unknown, part in growth. 824 EFFECT OF CHEMICAL AGENTS (Cu. XI Silicon. — This element is of wide occurrence among organ- isms. In many plants, especially the grains and grasses, it is exceeded in abundance only by potassium. Among the lower organisms whole groups, e.g. diatoms, Radiolaria, and glass sponges, are characterized by the great amount of silica made use of. Even in vertebrates it is found wide-spread in the blood, gall, bones, feathers, and hair. The silicon required for ‘the body is gained by plants and lower organisms from the soluble silicates or silicic acid of the soil and waters ; by verte- brates, probably from plants. Although Sacus (87, p. 271) was able in 1862 to show that growth even of maize (about one-third of whose ash is silica) continues in the absence of silicon, yet some grains do better, according to WouLFF (’81), when that element is abundant. It is significant, likewise, that, as PoLecK (50) found, 7% of the ash in the albumen of the hen’s egg is silicon. Copper. — Brief mention may be made of the fact that this metal occurs in a great variety of organisms, but usually in minute quantity. It occurs as a physiologically important con- stituent of the hemocyanine of the blood of the squid (FRED- ERICQ, "78, p. 721), of crabs and lobsters, and of certain gas- tropods and lamellibranchs (FREDERICQ, ’79). 2. The Organic Food used by Organisms in Growth. — All organisms may use organic compounds as food ; all organisms which contain no chlorophyll, certain bacteria excepted, must do so. This organic food may consist of solutions of definite composition or it may consist of solid masses of plant and animal tissue composed of varied and indeterminate kinds of organic molecules. The former are made use of chiefly by plants ; the latter, by the higher animals. This distinction is, however, not a necessary and constant one, for on the one hand insectivorous plants and many fungi live upon solid masses which they digest, and on the other hand some of the Protozoa can be fed upon known solutions, and doubtless some of the higher animals could be likewise fed, although few experiments seem to have been made in this direction. Even in methods of nutrition there is no sharp line to be drasen between the different groups of organisms. a. Fungi. — Our knowledge of the effect of known chemi- § 1] UPON THE RATE OF GROWTH 325 cal compounds used as food has been much more advanced by studies upon this group than upon any other. Yeast and bacteria have been especially investigated, but valuable results have been obtained upon the higher fungi also. Con- sidering all these results together, it appears that the nutritive value of an organic compound is perhaps chiefly determined by its assimilability; that is, the less the energy required to attack and transform the compound by the various chemical means at hand, the more favorable it is as a food. This assimilability depends in turn upon the molecular structure — upon a certain molecular instability or lability — upon the possession of that quality which is found in its extreme expression in many organic poisons. As Lorw (91, p. 761) has expressed it: Poison action, like nutritive action, is a relative conception. An indifferent body can become, by entrance of one atom-group, a nutritive substance; by entrance of an additional atom group, a poison. While a certain lability—that is, a certain degree of ease of decomposition —is a condition of the nutritive quality of a substance, a slight increase of this lability can give it a poisonous character, especially when the loosely arranged atoms can link into that atom-grouping upon which the vital movement in the protoplasm depends. Thus methan is indifferent for bacteria, methylalcohol is a nutritive sub- stance, formaldehyd is a poison, and its combination with sodic sulphate again a nutritive material.* Additional laws of nutritive value which hold true in many cases are as follows: The assimilable carbon compounds con- tain the group CH, or at least CH. Under otherwise similar conditions, compounds with one carbon atom are assimilated with great difficulty (methylamin) or not at all (formic acid, chloral); and, in general, but with important exceptions in the case of certain classes of substances, the assimilability increases as the number of carbon atoms in the molecule increases. The * The graphic formulas of these substances are : — OH OH x # CH, CH;-OH CH, CHz ‘ox soata, methan, methylalcohol. formaldehyd. formaldehyd-sodic sulphate. 326 EFFECT OF CHEMICAL AGENTS (Cu. XI radical HO- is usually easily released, consequently we find compounds containing this radical in general more assimilable than allied compounds in which the HO- is replaced by H. Especially is this true when the HO- is joined with radicals containing carbon and hydrogen atoms. For example, foods with the radical -CH,:OH are more nutritive than those with -CH,. Hydroxylized acids are better food for bacteria than non-hydroxylized — lactic acid, C,H,O3, is better than pro- pionic acid, C,H,O,. It is, perhaps, a special case under this rule that multivalent alcohols —7.e. those containing several HO groups—are better foods than the univalent ones; for instance, glycerine, CH,OH-CHOH-CH,OHW, is better than propylaleohol, CH,.CH,-CH,OH. Finally, the entrance of the extremely unstable aldehyd (-CH:0O) and keton (-CO-) groups increases the nutritive capacity of the food; for example, glucose, CH,OH - (CH -OH),CHO, or fructose, CH,OH . (CH - OH), -CO.CH,OH, is better than mannit, CH,OH.(CH-OH),-CH,OH. But all substances containing the group CHOH are good foods, since this compound can be used directly in the construction of carbohydrates, and eventu- ally of albumen. As an example of the application of these general principles may be given this series of substances arranged in the order of their decreasing nutritive value for yeast and molds (NAGELI and Lorew, ’80): 1, sugars; 2, mannit, glycerine, the carbon groups in leucin ; 3, tartaric acid, citric acid, succinic acid, the carbon groups in asparagin ; 4, acetic acid, ethylalcohol, kinic acid; 5, benzoic acid, salicylic acid, the carbon groups in pro- pylamine; 6, the carbon groups in methylamin, phenol. In conclusion may be mentioned a food for bacteria which, although inorganic, resembles organic compounds in that it may serve as a source of energy. This is the hydrogen disul- phide employed by the sulphur bacteria and allied forms (WINOGRADSKY, ’87, ’89). b. Green Plants. — It has already been shown that organic compounds can be assimilated by green plants. The experi- ments which have shown this have been made upon both alge and phanerogams, especially by Boxornyy, Lorw, A. MEYER, and LAURENT. It appears that, in the absence of carbon § 1) UPON THE RATE OF GROWTH 327 dioxide, Spirogyra may form starch from methylalcohol, for- maldehyd, glycol, methylal, acetylethylesteracetat, acetic acid, lactic acid, butyric acid, succinic acid, phenol, asparaginic acid, citric acid, acid calcium tartrate, ammonium tartrate, calcium bimalate, glycocoll, tyrosin, leucin, urea, hydantoin, kreatin, and peptones.* Phanerogams form starch from glycerine, cane sugar, levulose, dextrose, lactose, maltose, mannit, dulcit, and lecithin. While daylight favors assimilation it can be in some cases dispensed with. Thus the potato plant can accumulate starch in the dark when glycerine is used as food. An attempt to gain a deeper insight into the conditions of formation of albumen from organic matter has been made by HANSTEEN (’96), who reared Lemna in solutions of grape sugar or cane sugar, on the one hand, and amids, like asparagin, urea, glycocoll, leucin, alanin, or kreatin, on the other; also on grape sugar and inorganic nitrogenous bodies such as potassium nitrate, sodium nitrate, ammonium sulphide, and ammonium sulphate. Asa result of feeding on grape sugar alone at 20° C. during 24 hours, much starch was stored in the cells; when grape sugar and inorganic nitrogenous bodies were combined little starch and much albumen were produced. Much albumen was also gained when the nutritive solution contained cane sugar and urea, or asparagin and ammonium chloride, or asparagin and ammonium sulphate. The production of albu- men in green plants is favored by nitrogenous organic com- pounds. e. Animals. —These organisms are distinguished from the foregoing by an immense requirement of energy for their muscular processes, much of which is continually lost to the organism in the form of motion communicated to the environ- ment. On the other hand, growth is generally slower than in plants. Consequently in animal nutrition thermogenic foods are the more important and the nutritive processes are prevail- ingly exothermic. The plastic processes are the less striking ; nevertheless, it is they which chiefly concern us in our study of growth. ; Among the organic compounds ingested, carbohydrates are * The reagents were employed in about 0.1% solution, and whenever acid were neutralized with lime-water. 328 EFFECT OF CHEMICAL AGENTS [Cu. XI believed to have little importance as plastic foods—we have chiefly to consider the use of the complex fats, albuminoids, and other organic compounds. We can make little use of the extensive tables of calorific properties of foods which, however important for determining capacity for supplying energy, afford little insight into the plastic properties of the food — its importance for the growth of dry substance or the imbi- bition of water. The difficulties in the way of feeding animals upon known nutritive solutions are great, both because solutions are not their normal food, and because, in the case of water organisms, the bacteria introduced with the animals thrive better than they. Consequently the observations on nutritive compounds for animals are meagre. It will be best to consider them under the types upon which they have been made. Ameba. — We owe important studies on the foods of Amceba to the fact that some species have a pathogenic importance. Cultures of them have therefore been made by bacterio- logical methods. It is found that various, even innocuous kinds, will grow upon egg albumen in distilled or phenylated water kept at about 15° C. (CRIVELLI et Maaer, ’70, ’71; Mont, °95), upon agar-agar sheets from which the soluble substances have been removed by repeated washing in distilled water (BEYERINCK, 96), upon “ Fucus [Chondrus?] crispus” (CELLI, 796), or upon slices of potato (GORINI, °96). It is thus clear that, in addition to salts, Amceba needs only a very simple nitrogenous diet. It is, however, uncertain whether the amceba feeds directly from the organic food stuff, or indi- rectly upon the bacteria which grow upon the food supplied. Infusoria.— A beginning has been made in the study of this group by Fic. 90.— Polytoma uvella,) OGATA (’93), who reared pure cultures a flagellate infusorian. of the flagellate Polytoma uvella (Fig. (From VERWORN, 95.) 3 : 90) on plates of nutrient gelatine (which is extremely rich in protein) and also upon a medium composed of 500 ccm. meat bouillon, 12.6 grammes grape sugar, and 250 grammes of a Japanese mixture of alge called “nori,” derived mostly from the species Porphyra vulgaris. §1] UPON THE RATE OF GROWTH 329 The mixture was cooked, neutralized, filtered, sterilized, and infected with the flagellates, which had been isolated by means of capillary tubes. Here again growth was supported by simple, definite foods. Amphibia. —It is a great leap from Protozoa to vertebrates, but precise feeding experiments are almost lacking in the invertebrate Metazoa. In the present group come the pioneer experiments of Yune (’83). This author fed a number of tadpoles derived from the same batch of eggs upon foods of various kinds in unlimited quantity and under otherwise similar conditions. After forty-two days the size of the tad- poles in' each lot was measured and the following results were obtained : — TABLE XXXII ReEsvutts or Feepinc TapPoLes ON VaRiI0US SUBSTANCES No. oF VESSEL. 1 2 3 4 5 6 f AQUAzIO ALBUMINOTS PLANTS: PIECES OF ALBUMEN PIECES PIECES Kinps or Ece ENvVE- | ANACHARIS YOLK OF oF HEN’s oF Fiso oF BEEF Foop. LOPE OF . | AND Froc Hen’s Eee. Eee. Firsu. FLrsu. | Sprroeyra. : Length of tadpole 18.3 23.2 26.0 33.0 38.0 43.5 Breadth of . tadpole 4.2 5.0 5.8 6.6 8.8 9.2 It will be observed that the importance for growth was not proportional to the calorific properties of the respective foods, for the yolk of the hen’s egg has about 40% higher fuel value than dry egg albumen or dry flesh. The least growth occurred with a plant food which is relatively rich in carbohydrates, and has some protein and little fat; the third greatest growth occurred with the yolk, which has more fat than protein ; next comes egg albumen, with more protein than fat; and, finally, fish and beef flesh, characterized by their high percentage of nitrogenous matter. The tadpole grows fastest on a highly nitrogenous diet. 330 EFFECT OF CHEMICAL AGENTS (Cu. XI Additional experiments upon the frog’s egg have been made by DaniLewsxy (95), who found that such eggs placed in water containing z4,, of lecithin gained in 54 days 300% greater weight than those reared in pure water. The author believes, however, that this small quantity cannot act in a directly nutritive manner but, rather, that it favors in some way the assimilation of food. Mammals. — The requirements of agriculture have led to numberless experiments upon the feeding of domesticated mam- mals. Yet they are for the most part of little value for our purpose. A few of the better class of experiments from our point of view may be given, together with such conclusions as they permit. Years ago, Lawes and GILBERT (53), from extensive feed- ings of sheep and pigs, upon diverse foods, reached the conclu- sion that those “apparently grew more where, with no defi- ciency of other matters, the nitrogenous constituents were very liberally supplied. Hence, the gross increase obtained might be somewhat more nitrogenous with the large supply of nitrog- enous food; but it would in that case, according to some experiments of our own, contain a larger proportion of water, and less of solid matter, than where more fat had been pro- duced.” More recent studies made on various domesticated animals tend to confirm these results. A mixed diet with an abundance of nitrogenous food permits of greater growth than an equal quantity of food of one kind, or mixed food in which the nitrogenous constituent is scant. Growth tends to increase with the quantity of nitrogenous food rather more closely than with that of the non-nitrogenous food devoured. This conclusion is sustained by the striking results gained by PrésHER (97) in investigating the cause of the varying percentage rate of growth of different mammals. The rela- tion between growth and the percentage of the different organic and certain mineral constituents of milk is given in the following table : — § 1] UPON THE RATE OF GROWTH 331 TABLE XXXIV SHow1ne ror Various MAMMALS THE TIME REQUIRED TO DOUBLE THE BirRTH- WEIGHT, THE PERCENTAGE OF DIFFERENT ORGANIC CONSTITUENTS IN THE Mitk, AND THE RELATIVE QuanTITY OF ALBUMEN, CALCIUM OXIDE, AND Puospnoric Acip IN THE MILK OF THE DIFFERENT SPECIES— THE QUAN- TITY IN MAN BEING TAKEN AS THE STANDARD 1 2 3 4 5 6 7 8 RELATIVE RELATIVE| RELATIVE| RELATIVE SPECIES. utero: To as To To Quantity | QUANTITY | QUANTITY DouBLE Fat. Scuear. |ALBUMEN. ALBUMEN.| CaO. P205. WEIGHT. Man. ¥ 8 1 3.5 6.6 1.9 1.0 1 1 Horse . <« 3 11 6.1 2.3 1.2 4 3 Ox . a i 4.5 4.5 4.0 2.2 5 4 Bige > xg vg ale 6.9 2.0 6.9 Sut = = Sheep) « « «=| ve 10.4 4.2 7.0 3.8 8 9 Doge aivacct. gl Mas 10.6 3.1 8.3 4.45 | 14 10 Cat: & ees a ORE 3.3 4.9 9.5 5.1 = = From this table it is clear that there is a close relation between rate of growth and the percentage of albumen only among the organie substances of milk. This relation is best brought out by comparing columns 2 and 5. The last two col- umns show a close relation between growth and the quantity of calcium and phosphorus in the milk. But of the organic substances the quantity of the nitrogenous compound deter- mines the rate of growth. 3. Growth as a Response to Stimuli.— Hitherto we have regarded the process of growth in too mechanical a way, as though certain nutritive compounds, passing into a chemical mill, were inevitably transformed, at a certain rate, into proto- plasm or formed substance. We have now to recognize that the growth processes are essentially vital processes, and, as such, characterized by all that complexity which we find in such a vital process as response to stimuli. a. Acceleration of Growth by Chemical Stimulants. — Many chemical agents which are not themselves food may stimulate the growth processes. We have already seen (p. 51) how certain poisons cause, in dilute solutions, accelerated move- 332 EFFECT OF CHEMICAL AGENTS (Cu. XI ments and heightened metabolism. To the cases previously given may be added the experiments of ScHuLz (88), who found that various poisons, such as corrosive sublimate, iodine, bromine, and arsenious acid, increase the activities of yeast in fermentation. It is not strange, therefore, to find that poisons may, at a certain concentration, accelerate growth. That they do so follows from the experiments of RicHARDSs (’97), who reared the molds Aspergillus, Penicillium, and Botrytis in nutritive solutions to which had been added small quantities of zine sulphate, other metallic salts, cocaine, morphine, and other alkaloids. After five to seven days Aspergillus, reared in nutritive solutions in which sugar was the organic compound, had gained the following dry weights (in milligrammes). In all the experiments, except those in the column headed “Control,” the solution contained certain non-nutritious sub- stances in from 0.002% to 0.033% concentration. TABLE XXXV SHowine THE Tota Dry Weicut in MILLIGRAMMES OF A CROP OF ASPER- GILLUS REARED IN THE ABSENCE AND IN THE PRESENCE OF VARYING QuanTITIES OF IRRITATING SUBSTANCES SUBSTANCE. ControL. | 0.002% 0.004% , 0.008% 0.016% 0.033% ZnSO4 335 730 760 765 770 715 NaFl 250 565 405 340 270 245 NagSiOs 350 520 575 450 435 380 CoSOg 245 405 350 235 170 75 Cocaine 280 410 820 350 390 540 Morphine 160 155 170 140 210 215 It is clear from this table that the addition of even small quan- tities of innutritious and poisonous substances may so excite the hylogenic processes as to cause twice or even far more than twice the normal formation of dry substance in a given time, and that this excessive growth increases with the concentration of the salt up to a certain optimum, beyond which growth declines again to below the normal. Similarly TowNsEND C97) has observed that a seedling living under a bell jar whose atmosphere contains a small quantity of ether grows § 1) UPON THE RATE OF GROWTH 333 faster than one under similar conditions but without ether. If the plant is subjected to an increased quantity of ether, growth is retarded. The effect of these poisons is thus very different from that of nutritive substances; it is due to the irritating properties of the poison. b. The Election of Organic Food.—Not all of the food-stuff presented to the organism is utilized by it—neither, on the one hand, all of the kinds of food, nor, on the other, all of the food of the most acceptable kind if offered beyond a certain amount. There is an election of kind and of amount. A study of an election of kind has been made by DucLaux (’89), and, especially, Prerrer (95). The method employed was this: To the organisms (various molds, Aspergillus, Penicil- lium, etc.) were offered two compounds; one more nutritious, the other less so. Under these circumstances, the more nutri- tious compound was usually taken by the organism, while the less nutritious was often left entirely alone; thus, dextrose was preferred to glycerine, peptone to glycerine, and dextrose to lactic acid, even when, in each case, the quantity of the latter substance was in excess of the former. The election was not, however, always of the more nutritious material, so far as we can judge of relative nutritiveness. Thus, when Aspergillus was sown on a nutritive fluid, containing 8% dex- trose and 1% acetic acid, proportionally far more of the latter was assimilated than of the former, although the latter is of less value as food, as was shown by the fact that the plant had also to devour a considerable quantity of the dextrose. This extensive assimilation of a slightly nutritive substance is not, so far as we can see, an adaptive process. The character of the election may change with age, so that what is favorable for growth at one time is not at another. Thus DucLaux (’89) found that alcohol restrains or arrests the germination of the spores of molds, whereas it is made use of almost as abundantly as sugar by the adult plant; so, like- wise, lactose and mannit cannot nourish young plants when they replace sugar in the nutritive solution, whereas they are a good food for the older plants. So, also, among vertebrates, the food of the young, supplied in the egg or in the milk of the parent, is very unlike that 334 EFFECT OF CHEMICAL AGENTS (Cu. XT which is most favorable for growth in later stages. So impor- tant is this difference of food at different ages that agriculturists persistently change the ratio of the different foods supplied as their animals increase in age. The reason for this change in food required lies doubtless in this, that the chemical processes of growth change with the age of the animal; at first imbi- bition of water predominates, then comes the secretion of the various formed substances of the organism and the constant maintenance and increase of the plasma. The most favorable food of an organism at any time is dependent upon the metabolic processes going on at that time. The election of quantity is not less striking. It is well known that an increase above a certain limit in the amount of food presented to an organism or even actually taken into its body does not result in any increase in growth. There is a certain amount, fixed within broad limits, which corresponds to a maximum of nutritiveness. This amount, this feeding capacity, is not, however, necessarily constant at all stages of the adult growth of the organism. For it has been observed in certain animals, e.g. pigs, that as they grow older there is a steady increase in the amount of food required to produce a pound of gain in weight. Such facts serve to indicate that the rate of growth is largely determined by internal factors. Let us now summarize the results of this study of the effect of chemical agents upon the rate of growth. Of foods, those used in the plastic processes are chiefly to be considered. The substances serving as plastic food must contain all the elements normally occurring in the organism. These are found in di- verse proportions in different organisms, and hence the neces- sity of dissimilar foods. Not only carbon, oxygen, hydrogen, and nitrogen are necessary, but a whole series of other elements, such as phosphorus, sulphur, chlorine, iodine, sodium, potas- sium, calcium, iron, and magnesium are more or less essential. The organic plastic food varies with the group of organisms. Of relatively little importance for green plants, it becomes essential to fungi. In this group we find the most important character of a nutritive substance to be a certain degree of lability. Among animals a mixed diet is especially beneficial, but nitrogenous food favors growth more than non-nitrogenous § 2] UPON THE DIRECTION OF GROWTH 335 food. Finally, growth must be studied as a response to chem- ical agents which may stimulate the protoplasm to absorb and assimilate them to the degree required by the organism, or which may stimulate the protoplasm to absorb some other sub- stances, as we have seen in the case of zinc sulphate. The quantity and quality of food needed will, moreover, vary with the age and other qualities of the organism. The consumption of food both in quantity and in quality will be closely deter- mined by the demand. All these complexities in the process of nutrition indicate that it, like other processes in organisms, can only be explained on the assumption of a vastly complex molecular organization of the protoplasm. ‘§ 2. ErrEcT oF CHEMICAL AGENTS UPON THE DIRECTION or GROWTH — CHEMOTROPISM One of the most common processes in the early development of organisms is the turning or bending of a filament, tubule, or lamella. The cause of this turning is clearly an unequal growth of the two sides of the organ. When the bending organs are internal, their movements are largely removed from experimental study; when external, as in plants, they more easily lend themselves to our investigation. The object of this investigation is always to find in how far the direction of these tropic movements is determined or is determinable by external agents. In the present section it is proposed to consider in how far tropic movements are determined by chemical agents. At the outset it must be said that the growth which gives rise to these bendings is frequently due to imbibition of water; and in such cases it may be only temporary. Yet these temporary bendings pass by such insensible gradations into permanent ones that a sharp distinction between the two is impracticable and unim- portant. Rejecting such a classification of the subject, we may adopt one based on the tropic organ. 1. Chemotropism in the Tentacles of Insectivorous Plants. — This case of chemotropism was the earliest to be observed ; it was DARWIN (’75, p. 76) who first called attention to it. He found that when drops of water or solutions of rion-nitrogenous 336 EFFECT OF CHEMICAL AGENTS (Cu. XI compounds are placed upon the leaves of the sundew, Drosera, the tentacles remain uninflected; but when a drop of a nitroge- nous fluid, such as milk, urine, albumen, infusion of raw meat, saliva, or isinglass, is placed on the leaf, the tentacles quickly bend inwards over the drop. DARWIN now set to work sys- tematically to determine which salts and acids cause and which do not cause inflection. Of nine salts of ammonia tried, all caused inflection of the tentacles, and of these the phosphate of ammonia was the most powerful. Sodium salts in general cause inflection while potassium salts do not. The earthy salts are in general inoperative, as are likewise those of lead, manganese, and cobalt. The more or less poisonous salts of silver, mercury, gold, copper, nickel, platinum, and chromic and arsenious acids produce great inflection with extreme quick- ness. Other substances which caused inflection were nitric, hydrochloric, iodic, sulphuric, phosphoric, boracic, and many organic acids; gallic, tannic, tartaric, citric, and uric acids alone being inoperative. In all these cases, where a bending of the tentacles over the drop occurs, the turning must be regarded as a response to the stimulus of the chemical sub- stance. An excitation proceeds from the irritated region to the protoplasm upon whose imbibitory activity the turning of the tentacles depends. 2. Chemotropism of Roots. — Attention was directed to the fact that roots turn towards or from chemical substances by Mo.uiscuH (84), who experimented with gases. When grains of maize or peas are sprouted in water, their roots will turn Fic. 91.—Seedling of Zea, whose radicle originally was just touching the water obliquely with its apex and thereafter nutated in characteristic fashion, keeping close to the air. (From Mo.iscu, ’84.) § 2] UPON THE DIRECTION OF GROWTH 33T upwards towards the surface of the water —in response to the more abundant oxygen supply there (Fig. 91), and will grow along the surface of the water. Moxisca undertook a sys- tematic investigation of the action of various gases in con- trolling this growth. The method employed was as follows: The gases were enclosed in glass vessels whose mouth was closed by a plate of hard rubber perforated by slits, 2 cm. long by 2mm. broad. The vessel being laid on its side so that the slits were vertical, the rootlet of a germinating grain was placed in front of it. As the gas diffused from the vessel, it was for some time in excess upon one side of the rootlet. The gases experimented with were pure oxygen, pyrogallic acid, nitrogen, carbon dioxide, chlorine, hydrochloric acid gas, illuminating gas, ammonia, nitrous oxide, ether, chloroform, and oil of turpentine. In all cases there occurred, generally after about an hour, a turning of the root towards the gas (positive aérotropism, MouiscH), followed by a marked curvature from the slit (neg- ative aérotropism). Since decapitated roots respond in the same way as intact ones, but in less degree, MOLISCH con- cluded that the gases affect the growing region directly and do not require the intervention of the root-tip. 3. Chemotropism of Pollen-tubes.— The suggestion was early made by PFEFFER (’83), as a consequence of his discovery of chemotaxis in swarm-spores, that perhaps the bending of the antheridium-tube of Saprolegnia towards the odgonium was a case of response to a chemical agent. STRASBURGER (’86) offered a similar suggestion for phanerogams. PFEFFER (’88) then made experiments, but was unable to control the direction of growth of pollen-tubes. Moxiscu (89 and °93) was next led to undertake further study in this direction by the obser- vation that, when various pollen-grains are germinating in a nutritive drop and a cover-glass is placed over them, the pollen- tubes, after approaching near to the edge of the cover-glass, turn away towards the centre again (Fig. 92,a,6). The move- ment from the margin of the cover-glass cannot be ascribed to a difference of density produced by evaporation at the margin, for it occurred in a saturated atmosphere; nor can it be due to surface tension of the bounding film of water, for the turning occurred before the surface film was reached. These results Zz 338 EFFECT OF CHEMICAL AGENTS [Cu. XI were abundantly confirmed by Mryosnz (94), so we must conclude that the pollen tube is negatively aerotropic to oxy- gen. However, this negative aérotropism does not occur in all pollen, for that of Orobus vernus and various other legumes, of Primula acaulis, Viola odorata, V. hirta, etc., were indifferent. His Fic. 92. — Illustrates chemotropism of pollen-tubes. a. Negative chemotropism with reference to the air (aérotropism) of pollen-tubes of Narcissus tazetta; the tubes are growing under a cover-glass in a 7% sugar solution and turn at the edge, u,b, from the air; magnified about 20. 6b. Negative aérotropism of pollen-tubes of Cephalanthera pallens, after 20 hours; u, b, edge of caver-glass. c. Stigma of Narcissus tazetta in 7% sugar solution; pollen-tubes grow towards the stigma; magnified about 10. (From MoriscH, ’93). A second class of chemotropisms is seen in the turning of pollen-tubes towards the stigma of a flower.* When pollen is sown upon a plate of agar-agar or gelatine on which the upper end of a ripe pistil has been placed, the tubes are sent out in * Mouiscu accounts for the failure of some of the earlier experiments with pollen-tubes on the ground that certain pollen-tubes do not exhibit this class of chemotropism. Among these are Viola odorata, V. hirta, Orobus vernus, etc. — species which are likewise not aérotropic. § 2] UPON THE DIRECTION OF GROWTH 339 all directions at first, but quickly grow towards the pistil (Fig. 92,¢). Miyosui (94*) found that the top of the pistil was most attractive and that lower sections were less so until the ovary is nearly reached, when the attraction is high again. If the ovules of Scilla are placed on the plate of agar with its own pollen, the pollen-tube will even grow into the micropyle of the ovule. Pollen-tubes of a different species or even genus, e.g. Diervilla rosea, Ranunculus acer, etc., may likewise enter the Scilla ovule, and even hyphz of Mucor stolonifer will turn towards the ovules and penetrate into them. Thus the attract- ing stuff is not a specific stimulant confined in its activity to one kind of pollen-tube nor even to pollen-tubes in general. The nature of the attracting substance has been studied by Mryosui. Glucose is certainly present in the fluid excreted by the ripe stigma of many phanerogams; and, if the agar-agar substratum contain a 2% solution of cane sugar, there is no longer chemotropism with reference to the ovule, since now the attraction is not confined to a particular point. So it may be concluded that it is the sugar of the ovule or stigma which attracts the pollen-tube and that the excreted fluid contains about a 2% solution. Consequently, the chemotropism of pollen-tubes may be only a special case of chemotropism to sugar. Further experimentation confirmed Mryosur (9+) in this conclusion. Using the method employed by him in the case of hyphe (p. 340), he injected Tradescantia leaves with various solutions and sowed pollen of Digitalis purpurea upon the leaves. When pure water was injected there was no effect, but the substances named in the following list attracted the pollen-tubes so that they grew down through the stomata into the leaf: — cane sugar . 2-S% levulose . 1% (slight action) grape sugar, 4-8% lactose . 1-2% (‘slight ”) dextrin . . 12% The following solutions were neutral :— maltose. . . . . 1% asparagin . . . 2% meat extract . . . glycerine . . . 2-5% peptone. . ... gum arabic . . 2% 340 EFFECT OF CHEMICAL AGENTS [Cu. XI The following were repellent : — alcohol . . . . 01% potassium sulphate. 1% ammonium sulphate, 1% sodium malate . 0.5-2% It will be observed that all the attracting substances are sugars. 4. Chemotropism of Hyphe.— While various authors had noticed an apparent movement of hyphe towards certain chemical agents or towards their hosts, the earliest systematic observations upon this subject are those of WORTMANN (87). He placed fly-legs and other nutritive substances in Saprolegnia cultures and noticed that the hyphe left their original direc- <— —\ cs = ) eae, Fic. 93. — Negative chemotropism of a hypha of Peziza trifoliorum from the secre- tions of a mycelium of Aspergillus niger. (From REINHARDT, ’92.) tions to grow straight towards the food substance. Later REINHARDT (’92) showed that hyphe of Peziza may be lured out of their straight direction by spores of Mucor placed near them; or, again, if a plate of gelatine rich in sugar be placed above a plate of pure gelatine upon which hyphe of Peziza are growing, all hyphe will send up branches to meet the more nutritive surface; or, again, if Aspergillus niger, whose secre- tions are fatal to Peziza, is placed near the latter, the hyphe cease to grow at a distance of about 2mm. from the Aspergillus and then send out shoots which grow away from the injurious substance (Fig. 93). The most exhaustive studies on this subject are, however, those of Miyosu1 (9+), who worked with germinating spores of Mucor inucedo and M. stolonifer, Phycomyces nitens, Peni- cillium glaucum, Aspergillus niger, and Saprolegnia ferox. Perforated membranes were employed, either in the form of plant epidermis with stomata or of collodion films perforated § 2] UPON THE DIRECTION OF GROWTH 341 by a fine needle point. The solutions were injected into the leaf of Tradescantia, spores were sown upon its stoma-bearing surface, and the whole was kept in a moist chamber. If the solution was attractive, the growing hyphe penetrated into the stomata, whereas in the absence of the solution they showed no ‘tendency to do so. Similarly, spores sown on the perforated plate sent hyphe downwards through the holes when the plate was floating on attractive solutions, but not otherwise. Mole- Fic. 94.— Upper figure: Piece of the under side of a leaf of Tradescantia discolor injected with 2% ammonium chloride, and sown with spores of Mucor stolonifer. The young hyphz show chemotropic turnings, and have eventually penetrated into the stomata. Drawn 27 hours after sowing the spores; magnified 100. Lower Jigure: Penicillium glaucum growing on a leaf of Tradescantia, which has been injected with a 2% solution of cane sugar. The hyphe have branched, and the branches have penetrated into the stomata. Drawn 25 hours after sowing the spores; magnified 70. (From Mryosut, ’94.) cules diffusing out from the solution through the openings determine the direction of the growing hyphe, so that from all directions hyphe grew radially towards the openings in the membranes (Fig. 94). To prove that the result gained was truly chemotropism, and not something else, a series of experiments was made. That it was not a response to gravity was shown by sowing the spores below as well as on top of a leaf; that it was not a response to light or moisture was shown by keeping the cult- 342 EFFECT OF CHEMICAL AGENTS [Cu. XE ures in a dark, moist chamber ; in both cases, the chemotropic responses occurred. That contact was not the determining factor was shown by placing above and below sheets of perfo- rated collodion a layer of 5% gelatine, deprived of calcium salts, which are attractive. One of these layers was fertilized with grape sugar, the other remained sterile. The spores were sown sometimes in the sterile, sometimes in the fertile layer of gelatine; in the former case, the hyphe always grew (up or down) into the sterile layer; in the other case, they remained in the fertile layer. If both gelatine layers were sterile, or if both were equally fertile, the hyphz did not grow through the holes in the membranes. Not the holes, but the stuff diffusing from them, determined the direction of growth of the hyphe. There is a close relation between the chemical constitution of the agents and their effects. The following substances are attractive: compounds of ammonium (ammonium nitrate, chloride, malate, tartrate), phosphates (of potassium, sodium, ammonium), meat extract, peptone, sugar, asparagin, lecithin, etc. The following are neutral: glycerine and gum arabic (1 to 2%). The following are repellent: all free inorganic as well as organic acids, alkalis, alcohol, and certain salts, e.g. potassium-sodium tartrate, potassium nitrate, calcium nitrate, potassium chloride (2%), potassium chlorate (8%), magne- sium sulphate, sodium chloride (2%), ferric chloride (0.1%), phosphoric acid, etc. Comparing this list with that which PFEFFER and STANGE tried on swarm-spores (Pt. I, pp. 36- 38), we find that there is a rather close correlation. In both cases, glycerine (a good food) is neutral, alcohol repellent, phosphates attractive. As in the reaction of swarm-spores, so in those of hyphe, WEBER’s law is followed. 5. Chemotropism of Conjugation Tubes in Spirogyra. — This case is closely allied to chemotropism of pollen-tubes. Attention was first called to it by Ovrertron (88), who observed that at the point where the tubes were about to arise bacteria accumulated from the surrounding water. From this phenomenon, and on other grounds, he was led to conclude that a substance is excreted at this point which exercises a directive influence upon the conjugation tubes, insuring their meeting. This conclusion has been confirmed by HABERLAND LITERATURE 343. (90), who finds additional evidence for it in the character of the turnings which the two tubes from the opposite cells undergo in order successfully to impinge upon each other. The results of experimentation upon chemotropism show that various substances may direct the growth of such elon- gated organs as the tendrils, roots, and hyphe of plants; so that greater growth takes place on the side turned from the region of greatest concentration or towards it, as the case may be. In many instances it can be shown that the direction of growth is on the whole an advantageous one for the organism —so that the directed growth may be considered an adaptive one. In other cases, however, the response seems to have no- relation to adaptation. If that which controls direction is the unequal concentration of chemical agents in the medium, the immediate cause is. excessive growth on one side, due to excessive imbibition or to excessive assimilative activity. The relation between these causes is doubtless complicated. The chemical agent acts. upon the protoplasm, changing its molecular structure; the changed protoplasm exhibits changed growth activities. 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Ueber das Verhalten des Schwefels im Organismus und den Nachweis der unterschwefligen Siure im Menschenharn. Arch. f. path. Anat. u. Physiol. CXIX, 148-167. 2 Jan. 1890. Proéscner ’97. Die Beziehungen der Wachsthumsgeschwindigkeit des Siuglings zur Zusammensetzung der Milch bei verscheidenen Sauge- thieren. Zeitschr. f. physiol. Chem. XXIV, 285-302. 22 Dec. 1897. Purrewitscu, K. ’95. Ueber die Stickstoffassimilation bei den Schimmel- pilzen. Ber. D. bot. Ges. XIII, 342-345. 27 Nov. 1895. Ravuser, A. 84. Ueber den Einfluss der Temperatur, des atmosphirischen Druckes und verschiedener Stoffe auf die Entwicklung thierischer Eier. Sitzungsber. d. naturf. Gesell. Leipzig. -X, 55-70. Rautin, J. 69. Etudes chimiques sur la végétation. Ann. des Sci. Nat. (Bot.). (5), XI, 93-299. Reinuarpt, M. O. 92. Das Wachsthum der Pilzhyphen. Jahrb. f. wiss. Bot. XXIII, 479-599. Ricuarps, H. M.’97. Die Beeinflussung des Wachsthums einiger Pilze durch chemische Reize. Jahrb. f. wiss. Bot. XXX, 665-688. : Roos, E. 96. Ueber die Wirkung der Thyrojodins. Zeitschr. f. physiol. Chem. XXII, 16-61. 16 May, 1896. Sacus, J. v.’87. Vorlesungen iiber Pflanzenphysiologie. Leipzig, Engelmann. Scuimper, A. F. W.’90. Zur Frage der Assimilation der Mineralsalze durch die griine Pllanze. Flora. LXXITI, 207-261. Scuxiésine, T. fils et Laurent, E. ’92. Recherches sur la fixation de l’azote libre par les plantes. Ann. de l’Inst. Pasteur. VI, 65-115. Feb. 1892. 92. Sur la fixation de l’azote libre par les plantes. Ann. de J’Inst. Pasteur. VI, 824-840. Dec. 1892. Scuie@sine, T., and Mtnrz, A. ’77. Sur la nitrification par les ferments organisés. Comp. Rend. LXXXIV, 301-303. 12 Feb. 1877. "79. Recherches sur la nitrification. Comp. Rend. LXXXIX, 891-894. 24 Nov. 1879. ScHNEIDER, R.’89. Verbreitung und Bedeutung des Eisens im animalischen Organismus. Humbolt. WITT, 337-345. Sept. 1889. 95. Die neuesten Beobachtungen iiber naturliche Eisenresorption in thierischen Zellkernen und einige charakteristische Fille der Eisen- verwerthung im Korper von Gephyreen. Mitth. a. d. Zool. Stat. zu Neapel. XII, 208-215. 6 July, 1895. LITERATURE 349 Scuuz, H.’88. Ueber Hefegifte. Arch. f. ges. Physiol. XLII, 517-541. 20 March, 1888. ’93. Ueber den Schwefelgehalt menschlicher und thierischer Gewebe. Arch. f. d. ges. Physiol. L1V, 555-573. 7 July, 1893. Socin, C. A. ’91. In welcher Form wird das Eisen resorbirt? Zeitschr. f. physiol. Chem. XV, 93-193. 10 Jan. 1891. Sroxiasa, J. ’96. Studien iiber die Assimilation elementaren Stickstoffs durch die Pflanze. Landw. Jahrb. XXIV, 827-863. SrrasBurGeR, E.’86. Ueber fremdartige Bestaubung. Jahrb. f. wiss. Bot. XVII, 50-98. Tammany, G. ’88. Ueber das Vorkommen des Fluors in Organismen. Zeitschr. f. physiol. Chem. XII, 322-326. TappPeiner, H. 93. Ueber Ablagerung von Fluorsalzen im Organismus nach Futterung mit Fluornatrium. Sb. Ges. Morph. u. Physiol. Munchen. VIII, 22-26. TownsEND, C. O.’97. The Correlation of Growth under the Influence of Injuries. Ann. of Bot. XI, 509-532. Vines, 8. H. 86. (See Chapter VIII, Literature.) Votxmann, A. W.’74. Untersuchungen iiber das Mengenverhiiltniss des Wassers und der Grundstoffe des menschlichen Korpers. Ber. d. Sachs. Ges. d. Wiss., Leipzig. XXVI, 202-247. Wierter, A.’83. Die Beeinflussung des Wachsens durch verminderte Par- tidrpressung des Sauerstoffs. Unters. a. d. bot. Inst. Tiibingen. I, 189-232. Winograpsky, S. ’S84. Ueber die Wirkung dusserer Einfliisse auf die Entwicklung von Mycoderma vini. Arb. St. Petersburger Naturf. Ges. XIV, 1382-135 [Russian]. Abstr. in Bot. Centralbl. XX, 165-167. ’87. Ueber Schwefelbacterien. Bot. Ztg. XLV, 493 et seq. 89. Recherches physiologiques sur les sulphobactéries. Ann. ]’Inst. Pas- teur. IIT, 49-60. Feb. 1887. *90. Recherches sur les organismes de la nitrification. Ann. 1’Inst. Pasteur. IV, 257-275. May, 1890. 95. Recherches sur l’assimilation de l’azote libre de l’atmosphére par les microbes. Arch. des sci. biol. de St. Petersb. III, 297-352. Wo rr, E. v.’81. Ueber die Bedeutung der Kieselsiure fiir die Haferpflanze Landw. Versuchs-Stat. XNVI, 415-417. 65. Mittlere Zusammensetzung der Asche, aller land- und forstwirth- schaftlichen wichtigen Stoffe. Stuttgart, 1865. Worterine, H. W. F. C. 95. Ueber die Resorbbarkeit der Eisensalze. Zeitschr. f. physiol. Chem. XXI, 186-233. 26 Nov. 1895. Worrmann, J. 87. Zur Kenntniss der Reizbewegung. Bot. Ztg. 812. Yune, E. 83. Contributions & Vhistoire de l’influence des milieux physico- chimiques sur les étres vivants. Arch. de Zool. (2). I, 31-52. CHAPTER XII THE EFFECT OF WATER UPON GROWTH We have already, in Chapter X, laid stress upon the impor- tance of the imbibition of water for the growth of both plants and animals. Here we may consider more in detail the rela- tion between growth and water, both as concerns the rate or quantity of growth and the direction of growth, or hydro- tropism. § 1. Errecr or WATER UPON THE RATE AND QUANTITY OF GROWTH It naturally follows from what we know of the importance of water for growth, that the rate of growth will be closely dependent upon water supply. And as all growth-phenomena have been better studied in plants than in animals, our further illustration of this fact will be drawn chiefly from the former. First, plant germination demands a certain minimal quantity of water. What this quantity is may be determined either by finding the least amount which will permit of normal germina- tion, or by measuring the amount absorbed by different seeds before protruding their radicles. This latter quantity has been shown by the careful determinations of HorrMANnn (’65, p- 52) to vary from between 40% and 60% of the original dry weight, in the case of various cultivated grains, to over 100% in the case of various Leguminose. In fungi, likewise, Lesace (95, p. 311) has found that there is a hygrometric limit below which Penicillium spores will not germinate; and that the interval elapsing before ger- mination begins is the shorter the moister the atmosphere. The method employed by Lesace is of wide applicability. The tension of the water-vapor formed above a saline solution is less than that formed above distilled water; and it diminishes in proportion to the concentration 350 §1) RATE AND QUANTITY OF GROWTH 351 of the solution. Indeed, to a given solution of a particular salt, e.g. sodium chloride, there corresponds a constant hygrometric state, however much the temperature may vary. This hygrometric condition may be calculated by the formula: 1—na, where saturation is taken as unity, n equals the number of grammes of sodium chloride dissolved in 100 grammes of water, and a is a constant factor, varying with the salt, and equal to 0.00601 in the case of sodium chloride. The spores were reared in a moist chamber, whose bottom was made by a plate full of the solution. The results of LESAGH’s experiments are given in the fol- lowing table : — TABLE XXXVI Snowine InTeRVAL IN Days ELAPSING BEFORE GERMINATION WHEN SPORES OF PENICILLIUM ARE KEPT IN Moist CHAMBERS OVER VARIOUS SOLUTIONS or Sopium CHLORIDE n 0 21.5 23.5 26.5 30-33.5 Interval. . . 1 6 9 11 No germination after 171 days From these results it follows by calculation that the spores ger- minate at the hygroscopic state of 0.82-0.84 or over, but not below this limit. The foregoing cases, taken from the two principal groups of plants, agree in showing that a certain amount of water is essential to the revival of the metabolic activities which are preliminary to germination. The large quantity of water absorbed by the seed or spore affords the mechanism or the stimulus to growth. Also, in the later stages of plant growth, the water both of the atmosphere and of the soil is essential. The importance of atmospheric moisture was shown by REINKE (76), who com- pared the size of the leaf-stem in different hygrometric condi- tions. The method of measuring was as follows: a young potted Datura (one of the Solanacez) was placed so that the lower half of one of its stems was horizontal. A fine platinum wire, suspended from a standard above, hung vertically near the stem, and made one turn around it. The lower.end of the wire carried a 2-gramme weight. That part of the wire which sur- rounded the stem was protected by a layer of tinfoil. As the stem swelled or grew thinner, the weight rose or fell. The vertical oscillation of the weight measured the variation in circumference of the stem. 852 THE EFFECT OF WATER (Cu. XII It appeared that as the atmospheric moisture increased, a considerable increase in the cross-section of the stem followed ; and as it diminished, the size of the stem diminished likewise. The results are graphically given in Fig. 95. T T a YY if L | S/ \ A Ss ee 4 2 °. aa ae oat | t Veer if i t i ere ete 12 10-|12 al a i oe eT | rere Coda [Oa Bs [ hd Cy n p= Fic. 95.— Curve of growth in thickness of a Datura stem, M-M, correlated with variations in relative humidity, H-H, the temperature T-T remaining nearly uni- form. The part of the curve falling below O-O indicates loss of thickness below the normal. The abscisse represent hours. (From REINKE, ‘76.) These experiments have been repeated by Francis DARWIN (93) upon the fruit of a gourd, Cucurbita, whose growth is little influenced by variations in temperature. He determined, by means of a delicate micrometer apparatus, the average incre- ment in microns per minute; and, at the same time, by means of a dewpoint thermometer, the moisture of the air. The relation between rate of growth and psychometric readings is best shown graphically, as in the curves of Fig. 96. The ' ' 1 t ol 10 Si t X/ i a ---J8 zx a sh oo ow E A | AS Lee Pa Me ec | gh Se ee ie O53 7 SLT BS 2 | 2 0 Ss u 12 1 Py 3 4 3 8 7 8 9 1 06 12th pa Fia. 96. — Curve of diameter of fruit of Cucurbita (full line) correlated with varia- tion in humidity (broken line). The abscisse represent hours; the ordinates represent growth in «4 per minute (numbers on the left) and per cents of humidity (numbers on the right). (From DARwIn, ’98). § 1) UPON THE RATE AND QUANTITY OF GROWTH = 353 figure shows plainly how, in general, an increment or a decre- ment in one of these quantities is accompanied by a corre- sponding change in the other. The cause of this relation between changes in volume and in moisture is partially explained by considering the quickness with which increased growth follows increased moisture. It is undoubtedly due, as TscHAPLOWITZ (86) has suggested, to the diminution in the transpiration of the plant in moist air as compared with dry air. The change in the rate of transpira- tion is, however, not to be conceived as an immediate physical result of the change in moisture, but as a response to the stim- ulus of greater or less water in the atmosphere. The amount of water in the soil also has an important influ- ence on the rate of growth. Quantitative studies on this well- known fact were afforded by HELLRIEGEL, who reared barley in soils which contained various fractional parts of the satura- tion quantity. Giving his results in the form of a table, we have the following relation between the humidity of the soil and the amount of dry matter produced, after a certain number of days, in the grain and in the chaff : — TABLE XXXVII Propuction, In Dry Matter, Houmipiry oF Sor. Grains. Chaff. 80%, 8.77 9.47 60 9.96 11.00 (Max.) 40 10.51 (AMlax.) 9.64 30 9.73 8.20 20 7.75 5.50 10 0.72 1.80 5 0.12 The principal conclusion that one can draw from this table is that there is an optimum humidity of the soil for growth, which is not, however, the same for all organs. More extensive researches upon this subject have been made by JUMELLE (‘89), who studied chiefly the effect of water upon the growth of the various organs of the plant, and by Qa 354 THE EFFECT OF WATER UPON GROWTH (Cu. XII GAIN ('92, 95), who studied the effect upon the entire plant, so that his results are of especial interest here. Gain planted seeds of various species in sand to which a little garden loam had been added. He was careful either to select seeds of equal size or, after sprouting had occurred, to weed out all but the normal, medium-sized ones. In one set of experiments, the soil contained from 3% to 6% of water; in the other, from 12% to 16% GAIN found that the entire plant grew faster in the humid than in the dry soil, as the accompanying diagram, Fig. 97, 20- GR. GR, (| { Oe t H ' ' f L ia 1MAY 1 JUNE Tuvr Fic. 97.— Curves of fresh weight of two similar seedlings of flax, one growing in moist, the other in dry, soil. The maximum weight (Jf) gained by the plant differs in the two cases, and also the time of gaining that weight. F, time of flowering ; fm, time of fructification. (From Gatn, ’95.) indicates. The aérial parts of the plant are more affected than the subterranean. The ratio of growth of plants in moist soil to those in dry varied from 1.12 (radish) to 2.33 (bean). § 2] HYDROTROPISM 855 Among animals the importance of moisture for the growing young is indicated by the fact that even in species living on the land or in the air the eggs and larve are frequently con- fined to moist situations, as in pulmonate gasteropods, in many insects, and in reptiles. When this is not the case, the eggs are provided with thick, water-containing envelopes, as in birds, or are placed on succulent leaves, or in special fluid- filled receptacles, as in many insects. Only rarely, as for example in the case of the meal worm, Tenebrio, and the Der- mestide, are the young found growing in a very dry medium. Doubtless in such cases the amount of water required for growth is less than in the cases where the larve develop in moist situations. To summarize, a minimal quantity of water is essential to germination and growth; and above this limit growth pro- ceeds more rapidly with the increase in water up to a maxi- mum which varies with the species. § 2. Errect or WATER ON THE DIRECTION OF GROWTH — HypRorropisM A growing organ, such as a leaf, root, or stolon, is normally in a condition of turgescence, as a consequence of the imbibi- tion of water. So long as the turgidity is equal on the two sides of the organ the latter retains its normal position. If the turgidity is diminished on one side, the organ bends towards that side; if it is increased on one side, the organ bends from that side. Thus, variations in cell turgidity cause changes in the position of organs. This inequality of turgescence on the two sides of an organ may arise in a homogeneous atmosphere; for certain organs have the capacity in a dry atmosphere of losing water on one side faster than on the other, and in a moist atmosphere of becoming more turgescent on one side than on the other. Con- sequently, the organ assumes a characteristic position accord- ing as the hygroscopic condition of the atmosphere is high or low. Such hygroscopic movements are of wide occurrence among plants, and are often highly adaptive. We see them, for example, in the folding of vegetative parts of the so-called Resurrection Plant of California (Selaginella lepidophylla), by 306 THE EFFECT OF WATER UPON GROWTH [Cu. XII which the whole plant is rolled into a ball capable of being transported by the wind, perchance to a moister region. These hygroscopic movements occurring in a homogeneous medium are to be distinguished from true hydrotropism, for they are not properly growth phenomena. True hydrotropism occurs in growing elongated organs, such as roots or stolons, which grow from or toward a region of greater or less moisture. The observations on this phenom- enon have not been numerous, and are difficult to bring under one point of view; consequently, we shall do best to classify the cases studied on the basis of the organs considered. 1. Roots. — The first studies upon hydrotropism in roots were made in the middle of the eighteenth century ; but they were crude and uncritical. The first adequate experiments were made by Knicut (11). He half-buried some beans in a flower-pot filled with earth, inverted the pot (in which the earth and seeds were retained by a grating), and kept the earth moist by adding water through the hole in the bottom of the pot. The radicles, instead of growing vertically down- wards as radicles normally do, ran horizontally along the sur- face of the moist earth. The same results were got by JoHN- son (29), who found in addition that if the mouth of the inverted flower-pot, or other seed receptacle, be placed in a moist atmosphere, the roots grow vertically downwards; they are no longer turned aside by dry air. Then DUCHARTRE (56) discovered that when a seedling was grown in relatively dry earth, with its aérial part in a close, moist chamber, the roots did not penetrate vertically into the soil, but grew out horizontally, and even upwards. Sacus (72) varied this experiment by planting his seeds in a basket made of netting, fixed to a metallic frame, and hung with its sides inclined at an angle of 45° with the horizontal plane. When the appa- ratus was placed in a damp chamber the radicles grew verti- cally downwards ; but in dry air they turned back towards the bottom of the sieve containing the damp earth, and ran along its under surface. SacuHs called especial attention to the fact that it is the damper side which becomes concave; and this shows that the turning is not due to direct physical causes. The second epoch in the study of hydrotropism now began. § 2] HYDROTROPISM 857 The fact of its existence being granted, the conditions of its occurrence were carefully studied. Thus Darwin (’80, Chap- ter III) investigated the locus of the irritable protoplasm. Some of the young bean-radicles were coated for the distance of a millimetre or two from the apex with a mixture of olive oil and lamp black in order to exclude the moist air. Such showed almost no hydrotropic movements. Jilling the tip by caustic produced the same result. Thus the terminal two millimetres or so include the irritable protoplasm. This conclusion was disputed by WIESNER (’81, p. 133) and DETLEFSEN (82) on the grounds that on the one hand coating or killing the tip introduced abnormal conditions to which the failure of hydrotropism might be ascribed, and, on the other hand, after the tip of the root was cut off a curving might still occur. However, a very careful review of the subject with new experiments by Mouiscu (8+), a pupil of WIESNER, con- firmed DARwin’s conclusion. Thus MouiscH covered all of the radicle excepting the terminal 1 to 1.5 mm. with wet paper. This upper part could then hardly be irritated by an unequal distribution of moisture in the environment. Never- theless, when a strip of moist filter-paper was placed opposite the tip the hydrotropic response occurred. The response must then have been due to a stimulus received exclusively at the tip, and it may be concluded that the tip alone is stimulated by moisture. Now, although only a millimetre or two of the tip is irritable, the response of bending takes place some distance, 7 to 28 mm., behind the tip, nearly in the region of maximum growth. Thus sensitive and responsive regions do not coincide — there is a transmission of stimuli. The facts that the hydrotropic response occurs in the region of rapid growth and that at the minimum temperature of growth response no longer occurs, indicate clearly that the hydrotropism of roots is not the result of mechanical loss of turgescence on one side, but that it is on the contrary a growth phenomenon — a localized growth which is a response to a stimulus. 2. Rhizoides of Higher Cryptogams.— While it is a priort probable that the rhizoids of hepatics should react like the roots of phanerogams, MouiscH desired to demonstrate the fact 358 THE EFFECT OF WATER UPON GROWTH (Cu. XII by experiment. Upon a glass dise was placed a piece of moist filter-paper so large that its edges hung vertically downwards as a flap beyond the margin of the disc. Thalli of various Marchantiacez were placed in sand at the margin of the dise in such a way that the young growing edge projected half a centimetre beyond. The disc and the object on it were ex- posed to daylight, but slowly rotated in a horizontal plane in order to eliminate phototropic action. The young, positively geotropic, rhizoids which developed beyond the margin of the dise did not grow vertically downwards, but turned towards the flap of moist filter-paper, thus proving that they are posi- tively hydrotropic. The same is doubtless true of the rhizoids of ferns. 3. Stems. — Very few studies seem to have been made upon the hydrotropism of the stems of seedlings; the most impor- tant are those of MoxiscH. Several sets of experiments were carried out upon seedlings of flax, pepper-grass (Lepidium sativum), bean, Nicotiana camelina, etc. The method employed was nearly that of WORTMANN (see below). Of these plants the hypocotyls of the flax alone showed any hydrotropism ; it may accordingly be concluded that stems are markedly hydro- tropic in but few seedlings. 4. Pollen-Tubes. —The reactions to moisture of these organs have been studied by Miyosur (94). He placed pollen-grains on the stigma of the same species and found that whereas in a dark, moist chamber the pollen-tubes grew in all directions, when dry air was admitted the pollen-tubes turned towards ‘the centre of the stigma. This turning is best explained as a response to the greater moisture surrounding the mouth of the stigma. It is clearly also an advantageous result, since it tends to direct the pollen-tube to the ovary. 5. Hyphe of Fungi.— While Sacus (79) early suggested that the sporangium bearer of Phycomyces nitens is negatively hydrotropic, the first experimental evidence on this point was offered by WORTMANN (81). Spores of Phycomyces were sown on bread kept in a moist chamber whose walls were made opaque to prevent phototropism. When, after three or four days, some of the sporangium-bearers had gained a height of one or two centimetres all were bent to one side excepting one which protruded § 2] HYDROTROPISM 359 through a small hole in the glass disc. Parallel to this hypha and close to it was placed a piece of soaked card. After 4 to 6 hours the hypha turned from the damp card; but when the card was dry no such turning occurred. The extraordinary sensitiveness of the sporangium bearing filaments of Phycomyces has been shown by the experiments of ErrarA (93). He found that these organs turned toward rusting iron, china-clay, agate (but not rock crystal), and sul- phuric acid. He explained this result on the ground that these substances absorb the moisture in their vicinity. Con- sequently the hydrotropic filaments turn towards this rela- tively dryer region. So sensitive, indeed, is this plant that it may be used to detect a very slight difference in the hygro- scopic properties of chemically related substances. Not only do the hyphe of Phycomyces turn from moisture, but, as MoxiscuH (83) showed, those of Mucor stolonifer and the telatively great trunk of the toadstool Coprinus velaris respond in the same way. The spores are thereby carried away from the moist situation. In conclusion a word may be said concerning the cause of hydrotropism. It is probable that two diverse phenomena are confused under the term. One of these is seen when a multi- cellular organ like the root of phanerogams is unequally moistened on opposite sides; the moister side will lose water less quickly than the other, or it may actually imbibe some. Its cells will accordingly become more turgescent and the whole moister side more convex. This result is due to a relatively direct, almost mechanical, cause ; it simulates nega- tive hydrotropism, but it is so different in kind from the true phenomenon that it may be called false hydrotropism. In the second class of cases we see multicellular organs, such as roots, becoming concave towards the slightly moister region, or unicellular organs, such as rhizoids, pollen-tubes and hyphee —organs which cannot be supposed to become unequally tur- gescent on the two sides — exhibiting a + or — turning. These cases cannot be explained on direct mechanical grounds ; they are responses to stimuli, and, as such, examples of true hydrotropism. These two kinds of hydrotropism may occur in the same organ under different conditions and thus cause turnings in 860 THE EFFECT OF WATER UPON GROWTH ([Cu. XII opposite directions. Thus WorTMANN (81, p. 374) finds that a mycelium growing downwards towards water turns horizon- tally before touching it and branches profusely. Similarly a root growing towards water will not penetrate into it, but will turn to one side. The greatly increased moisture causes the reversal of the tropism, but this is probably due to the fact that a false hydrotropism replaces the true response ; however, as true hydrotaxis may take place in both directions, so there may be a true negative as well as positive hydrotropism. I now summarize our conclusions concerning the effect of water upon growth. Water plays a part in growth second in importance to no other agent, so that in its absence growth cannot occur. As the quantity is increased, growth is increased until an optimum is reached. The amount imbibed does not, however, depend directly upon the amount available, but rather upon the needs or the habits of the species. Growth of elon- gated organs may take place from or towards moisture, and the turning may be a true response to the stimulus of higher or lower aqueous tension, —a response which may show itself in a bending at some distance behind the irritable tip. This response is, moreover, often of an advantageous kind, directing the rootlets towards water and the pollen-tube towards the moist stigma or keeping the sporangium in the dry atmosphere necessary for the production of dry spores. In a word, imbi- bition of water and growth with reference to the source of moisture are regulated to the advantage of the species. LITERATURE Darwin, C. ’80. The Power of Movement in Plants. London, 1880. Darwin, F. ’93. On the Growth of the Fruit of Cucurbita. Ann. of Bot. VII, 459-487. Pls. XXII, XXIII. Dec. 1893. DETLEFSEN, E. ’82. Ueber die von Ch. Darwin behauptete Gehirnfunction der Wurzelspitze. Arb. a. d. bot. Inst. Wiirzburg. II, 627-647. Ducuartre, P.’56. Influence de V’humidité sur la direction des racines. Bull. Soc. bot. France.. IIT, 583-691. Errara, L. ’93. On the Cause of Physiological Action at a Distance. Rept. Brit. Ass. Adv. Sci. for 1892, 746, 747. LITERATURE 361 Gain, E. ’92. Influence de l’humidité sur la végétation. Compt. Rend. CXYV, 890-892. 21 Nov. 1892. 95. Recherches sur la réle physiologique de l’eau dans la végétation. Ann. Sci. Nat., Bot. (7), XX, 63-215. Pls. I-IV. HorrMmann, ’65. . Beitrige zum Keimungsprocess. Lanudwirthsch. Versuchs- Stat. WII, 47-54. Jounson, H.’29. The Unsatisfactory Nature of the Theories proposed to account for the Descent of the Radicles in the Germination of Seeds, shewn by Experiments. Edinb. New Philos. Mag. VI, 312-317. JUMELLE, H. ’89. Recherches physiologiques sur le développement des plantes annuelles. Revue Générale de Bot. I, 101 et seq. Knicut, F. A. 711. On the Causes which influence the Direction of the Growth of Roots. Phil. Trans. Roy. Soc. London. Pt. I, 209-219. Lesacr, P. ’95. Recherches expérimentales sur la germination des spores die Penicillium glaucum. Ann. Sci. Nat., Bot. (8), I, 309-322. Nov. 1895. Mryosu1, M. ’94. Ueber Reizbewegungen der Pollenschlauche. Flora. LXXVIII, 76-93. Mouiscu, H. ’84. Untersuchungen iiber den Hydrotropismus. Sb. Wien. Akad. LX XXVIII}, 897-942. Taf. I. Reinke, J. ’76. Untersuchungen iiber Wachsthum. Bot. Ztg. XXXIV, 65-69, 91-95, 106-111, 118-134, 136-160, 169-171. Pls. H, III. Feb., Mar. 1876. Sacus, J.’72. Ablenkung der Wurzel von ihrer normalen Wachsthumsricht- ung durch feuchte Korper. Arb. bot. Inst. Wiirzburg. I, 209-222. 79. Ueber Ausschliessung der geotropischen und heliotropischen Kriim- mungen wihrend des Wachsens. Arb. bot. Inst. zu Wiirzburg. II, 209-225. TscnapLowiTz, F. C.’86. Untersuchungen tiber die Wirkung der klimat- ischen Factoren auf das Wachsthum der Culturpflanzen. Forsch. Agr. IX, 117-145. [Abstr. in Bot. Jahresber.] XIV, 57, 58. Wiesner, J. ’81. Das Bewegungsvermogen der Pflanzen. 212 pp. Wien, 1881. Wortmann, J. ’81. Ein Beitrag zur Biologie der Mucorineen. Bot. Ztg. XXNIX, 368-374, 383-387. June, 1881. CHAPTER XIII EFFECT OF THE DENSITY OF THE MEDIUM UPON GROWTH In this chapter we cannot, as hitherto, consider the effect of density upon both the rate or quantity and the direction of growth, for no studies seem to have been made upon the latter subject. § 1. Errect or DENSITY UPON THE RATE OF GROWTH We have seen in Chapter III (p. 77) that the increase or decrease in the concentration of a solution produces, by osmosis, changes in the structure of protoplasm, in its locomotion, and in its excretory activity. It remains to be seen to what extent change in density can affect the metabolic activities concerned in growth. The relation between the rate of growth of plants and con- centration has been the subject of much study, e.g. by WIELER (83), DeEVrigEs (77), JARIUS (86), JENTYS (88), ESCHEN- HAGEN (’89), and STANGE (’92). It is agreed that, in general, as the solution containing the plant becomes more concentrated the seedling or the fungus (JENTYS, p. 455) grows more slowly. The question now arises whether there is any maximum concentration at which growth is completely inhibited. Data on this subject are given by ESCHENHAGEN, who finds that various fungi will not grow at a concentration above the following limits :— STARCH. GLYCERINE, Sopium Nitrate. Coumow Sat. CoH 1206. C3H 05. NaNO3. NaCl. Aspergillus . . . 534, 43, 21% 17%, Penicillium . 55 43 21 18 Botrytis. ... 51 37 16 12 362 §1]) EFFECT OF DENSITY UPON RATE OF GROWTH — 363 Also Racrsorsxi (96) found that Basidiobolus cultivated in a nutritive solution containing 10% peptone, 1% glucose, and the necessary salts, ceased to grow when the concentration of the salts reached the following percents :— sodium chloride, NaCl, 6%. glycerine, C;H,0, 20%. potassium chloride, KNO;,11%. glucose, CgeH,0,, 25%. The foregoing maximum concentrations vary with the molec- war weights of the dissolved substances, indicating that their effect is purely an osmotic one. Germination is likewise affected by concentration, as a valu- able series of experiments by VANDEVELDE (’97) clearly shows. Seeds of the pea, Pisum sativum, were soaked for 24 hours in solutions of common salt varying from 1% to 35%, then removed, planted, and the percentage of seeds which germinated (G%) and the mean interval elapsing before germination (I) determined. (I) was, more precisely, the time elaps- ing (in days) before one half of the seeds had germinated. The results are given as follows : — TABLE XXXVIII SHOWING THE RELATION BETWEEN THE CONCENTRATION OF THE SOLUTION IN wHIcH PEAS HAVE BEEN SOAKED AND THEIR GERMINATION % | &% I % G% I % | @% I % G% I 1 | 98.00 | 2.1 | 10 | 12.46 | 5.9 | 19 | 4.00 | 5.7 | 28 6.83 | 5.7 2 | 97.17 | 8.7 | 11 7.00 | 6.6 | 20 | 5.67 | 5.7 | 29 3.83 | 6.7 38 | 85.17 | 4.0 | 12 | 10.00 | 6.3 | 21 | 3.83 | 7.0 | 30 | 10.83 | 6.5 4 | 34.50 | 4.6 | 18 8.50 | 6.8 | 22 | 1.50 | 5.6 | 31 8.83 | 6.8 5 | 32.66 | 4.8 | 14 7.19 | 6.38 | 23 ) 1.83 | 6.2 | 32 | 10.67 | 7.2 6 | 16.83 | 5.0 | 15 4.50 | 6.7 | 24 | 4.00 | 5.8 | 33° | 23.00 | 6.2 7 | 15.33 | 6.2 | 16 6.83 | 7.1 | 25 | 0.83 | 5.8 | 34 | 31.33 | 6.5 8 | 14.83 | 5.3 | 17 4.76 | 6.6 | 26 | 4.50 | 6.3 | 35 | 56.83 | 7.0 9 | 12.66 | 5.4 | 18 8.83 | 6.2 | 27 | 8.17 | 6.8 This table yields some remarkable results. As the concen- tration increases from 1% to 15%, the percentage of germina- tions diminishes from 98 to 4.5, and the mean germination interval increases from 2.1 days to nearly 7, near which point it remains at all higher concentrations. From 15% to 29% the percentage of germinations fluctuates so irregularly between 6.8 and 0.83 that within these limits it may be considered con- 364 EFFECT OF DENSITY OF THE MEDIUM § [Cu. XIII stant. As the concentration increases from 29%, instead of the grains all being killed or failing to germinate, we have the interesting result that the percentage of germinating individ- uals rises rapidly from 4 to 56. VANDEVELDE hazards the following explanation of this result: “Dilute solutions are easily absorbed; the more concentrated the solution, the smaller the power of diffusion; in a saturated solution the seeds do not swell and the action of the surrounding solution is less injurious.” But we need to know more of the condi- tions under which this result occurs before we can accept any interpretation. With animals we find growth similarly affected as with plants. Lor (92) first showed this in his experiments upon the regenerative growth of decapitated tubularian hydroids. The regenerating hydroids were kept in water more and less dense than, and equally dense with, sea water. At the end of eight days the length of the regenerated piece was measured in seven to nine individuals at each concentration. The results may be given in the form of a curve (Fig. 98) by laying off as abscissee the percents of sodium chloride in the water and as ordinates the corresponding average growth in millimetres : — NORMAL SEA WATER i) eo 2 3 | 4 5 6 DILUTE SEA WATER CONCENTRATED SEA WATER Fic. 98.— Curve showing the relation between the density of the medium and the proportional rate of growth of regenerating Tubularia. The maximum ordinate indicates 10.5 mm. growth in 8 days. The numbers at the base of the curve are per cents of density in excess of distilled water; thus ‘3’ signifies a specific gravity of 1.03. (From Logs, ’92.) This curve shows that the optimum concentration for growth is not, as might have been expected, the normal concentration, but one considerably below the normal, namely 2.5% instead § 1] UPON THE RATE OF GROWTH 365 of 8.8%. Anything which favors endosmosis seems, within certain limits, to favor growth. Regenerating annelids have also been studied at my labora- tory by Mr. J. L. Frazeur.