Practical physiology of plants

Front matter

AT CORNELL UNIVERSITY.

DATE DUE

1D wov 8) JL

Preface

N 1883 one of us began a course of instruction in the

physiology of plants, of which the chief feature was the demonstration of experiments in the lecture-room. Some years later a different arrangement was made, the students were required to perform the experiments for themselves ; and at the same time laboratory work in the chemistry of metabolism was organised by one of us. To enable the students to carry out their work, written instructions were needed, and the present book is the result of an extension and elaboration of what we prepared for our, classes.

The book makes no pretence to completeness, it contains merely such a selection of experimental and analytical work as seems to us suitable for botanical students.

Part I, which deals with general physiology, is necessarily of a somewhat more elementary character than Part JI, which treats a particular department of physiology in a more special manner, and presupposes a greater amount of knowledge on the part of the student.

D. A. b vi PREFACE.

The footnotes in Part I (which form an addition to the original draft of the work) merely supply a rough guide to some parts of the literature. Nor is any attempt made to give a full account of the literature of the subjects dealt with in Part II. The papers enumerated at the head of each chapter are merely recommended as being illustrative of the use, in actual research, of the methods. described.

We gladly take this opportunity of expressing our thanks to Mr F. F. Blackman, Demonstrator of Botany in the University, for much valuable help in the arrange-’ ment of the experiments in Part I. Also to the Cambridge Scientific Instrument Company for the use of the clichés for Figs. 25 and 26.

Botanica, LaBoRAToRY, CAMBRIDGE.

August 19, 1894,

Chapter I. On Some Of The Conditions Affecting The Life Of Plants

Section A. Respiration. Ei Respiration; accumulation of CO, produced by germinating seeds or buds. 2. Absorption of CO, bypotash. 3. Sachs’ method. 4, 5, 6. Intramolecular respiration. 7, 8,9. Rise of temperature during respiration. 10. Germination of oily seeds. 11. Succulents ‘i . ‘ ‘ 2 pp. 1—10.

Section B. The effect of various temperatures: of certain poisons: and of electrical shock. 12. Injurious temperature demonstrated on Oxalis leaf. 13. Do., injected leaf. 14. Do., beetroot. 15. Do., dry and soaked seeds. 16. Circulation of protoplasm, Sachs’ Hot-Box. 17. Velten’s method. 18. Circulation of protoplasm, effect of COQ,. 19. Do., chloroform. 20. Oxalis leaf killed by chloroform. 21. Do. by phenol. 22, Do. by induced current. 23. Effect of induced current on circulating protoplasm . : a A i % i a pp. 10—16.

b2

Vili CONTENTS.

Chapter II. Assimilation Of Carbon

Szcrion A. Formation of starch. 24. Sachs’ Iodine method, 25. Schimper’s method. 26. Variegated leaves. 27. Disappearance of starch in darkness. 28. Effect of dull light. 29. Local effect. 30. Gardiner’s experiment. 31. Rays of different refrangibility. 32. Terrestrial leaves under water. 33. Excess of CO,, 34, Plants deprived of CO,. 35. Temperature and assimilation. 36. ‘Gain in weight. 37. Translocation. 38. Assimilation of sugar. 39. Do., formaldehyde. 40. Leucoplasts. pp. 17—30.

Section B. Evolution of oxygen. i. Bubbles of gas. 42. Light of varying intensity. 43. Dependence on presence of CO,, 44, Temperature and gas evolution. 45. Chloroform. 46. Coloured lights. +47. Collection of gas evolved. 48. Engelmann’s blood method. 49. Phosphorus method. 50. Dehérain’s method. 51. Gas analysis, Pfeffer’s method. 52, Gas analysis, Winkler. Hempel apparatus. 53. Engelmann’s bacterial method. 54. Diffusion of gas through cuticle . . 5 . . pp. 30-43,

Section C. Reactions of chlorophyll and of some other pigments. 55. Separation by benzene, ether, olive oil. 56. Action of light. 57. Aeration and effect of light. 58. Action of acid. 59. Action of copper-salts, 60. Stability of the copper compound. 61. Spectroscopic examination. 62. Red colour of Ricinus, Coleus &e. 63. Floridese. 64. Brown sea-weeds . - pp. 48—46.

Section D, Production of chlorophyll, etiolation, sun- and shade-leaves. 65. Appearance of the green colour. 66. Etiolin and light. 67. Pinus. 68. Chlorophyll formation and temperature. 69, 70. Do. and oxygen. 71. Do. and iron salts. 72. Form of etiolated plants. 73. Sun- and shade-leaves.

Chapter III. Further Experiments On Nutrition

Srection A. Water-culture. 74, Method. 75. Potassium salts necessary. 76. Phosphoric acid necessary. 77. Experi-: ments with Lemna. 78. Calcium oxalate formation. 79. Nitrate reaction . : . : . . . : . : pp. 51—60.

CONTENTS. 1x

Section B, Nutrition of Fungi and of Drosera. 80. Method. 81. Various cultures. 82. Puccinia. 83. Hanging-drop cultures. 84. Germination of spores. 85. Drosera, digestion of white of egg. 86. Drosera, benefit from feeding 7 7 ‘ , pp. 60—66.

_ Secrion C, Functions of roots. 87. De Saussure’s experiment. 88, 89. Root pressure. 90. Moll’s experiment. 91. Absorption by means of dead roots . : ‘ : : - . pp. 66—71.

Chapter IV. Transpiration

Secrion A. Absorption of water. 92. Potometer. 93. Kohl’s method. 94, Effect of sunshine. 95, Effect of wind. 96. Effect of light. 97—100. Negative pressure. 101. Permeability of membranes. 102, Oozing of water from wood, 103. Permeability of splint-wood. 104. Injection of flaccid shoot. 105. Emulsion experiment. 106. Injection with cocoa-butter. 107. Compression. 108. Incisions. 109. Cross-cuts. 110. Do., course shown by eosin. 111. Air-pump and potometer. 112. Strasburger’s air-pump experiment . . : . 7 , . . pp. 72—-88. Section B. Loss of water. 113. Loss of weight during transpiration. 114, Transpiration compared with evaporation from water. 115. Loss compared with absorption. 116. Spring balance, pp. 88—93.

Section C. Stomata bloom lenticels. 117. Stomatal transpiration. 118. Stipa-hygrometer. 119. Stomata and intercellular spaces, 120, Leaf injected with water. 121. Frost effects. 122. Blocking of stomata with water. 123. Movements of stomata. 124. Do. with induced current. 125. Lenticels and intercellular spaces. 126, Bloom as affecting transpiration . pp. 98—100.

Chapter V. Physical And Mechanical Properties

Section A. Imbibition, hygroscopic movements, polariscope, osmosis. 127. Laminaria, microscopic observation. 128. Laminaria increase not uniform in all direction. 129. Imbibition of seeds, x CONTENTS.

temperature effect. 130. Imbibition; salt solution. 131. Stipa, action of. 132, 133. Stipa, temperature, 134, Stipa, salt solution. 185. Stipa, mechanism of movement. 136. Nobbe’s experiment. 137. Variability in the swelling of seeds. 138. Rise of temperature. 189. Work done during imbibition. 140. Polariscope. 141, Polariscope, observations on strained glass rods, 142, Traube’s artificial cells. 143. Slowness of diffusion, 144. Relation of membrane to diffusing fluid. 145, Absorption of methylene blue by living cell. é . ‘ ‘ s . pp. 101—113.

Szcrron B. Turgor. 146. Plasmolysis, microscopic observations. 147. Recovery after plasmolysis. 148. Osmotic strength of cell-sap in terms of KNO,. 149. Isotonic coefficient. 150. Do., microscopic method. 151. Hydrostatic pressure in turgescent tissue, 152. Pfeffer’sgypsum method. . . . #. pp. 118—121,

Section C. Tensions of tissues. 153. Longitudinal tensions, 154, Extension of pith in water. 155. Changes in transverse dimensions of pith. 156. Tangential dimension. 157. Shortening of roots. 158. Imperfect elasticity of tissues. 159. Cyclometer, 160. Hofmeister’s experiment. 161. Loss of rigidity. 162. Increase in length. 163. Splitting turgescent tissues. 164. Splitting a root, 165. Splitting a pulvinus ‘ . pp. 121—129.

Chapter VI. Growth

.

Section A. Experiments without special apparatus. 166. Method. 167. Free oxygen necessary. 168. Respiration necessary. 169. Full turgescence necessary. 170. Growth at various temperatures,

Section B. Distribution of growth. 171. Distribution in roots, 172. In air-roots. 173. In stems. 174. Grand period, time observation. 175. Growth and plasmolytic shrinking pp. 138—186.

Section C. Auxanometers. 176. Methods. 177. Descent of the weight measured on a scale. 178. Micrometer screw. 179. Are-indicator. 180. Microscope. 181. Self-recording auxanometer. 182. Do., simple form. 183, 184. Growth and temperature, microscopic method. 185. Growth and respiration, micro-

CONTENTS, xi scopic method. 186. Growth and temperature, auxanometer. 187. Growth and light, auxanometer. 188. Growth and light, Phycomyces. 189. Growth and light, Sinapis. 190. Periodicity, auxanometer . 2 . F "i . . r pp. 186—149.

Chapter VII Curvatures

Szction A. Geotropism, 191. Region of growth and region of curvature, roots. 192. Do., stems. 193. Subsequent change in curvature. 194. Grass-haulms. 195. Noll’s experiment, grass-haulms. 196, 197. Geotropism and respiration. 198. Johnson’s experiment, 199. Pinot’s experiment. 200. Knight’s experiment.

201. Sudden curvature. 202, 203. After effect . pp. 150—159,

Section B. CGurvatures due to injury &c. 204. Decapitated roots. 205. Decapitation prevents perception of stimulus. 206. Recovery after decapitation. 207. Curvature due to injury. 208. Ciesielski’s experiment. 209. Drooping of leaves in frost pp. 159—164.

Section C. Heliotropism. 210. Positive heliotropism. 211. After effect. 212. Light of high refrangibility most effective. 213. Negative heliotropism. 214. eiaes and ie acting together. 215. Transmitted stimulus . fi a : pp. 165—168.

Section D. Diaheliotropism, diageotropism &c. 216. Diaheliotropism. 217. Due to specific sensitiveness, klinostat. 2174. EHxclusion of helio- and geotropism. 218. Rectipetality. 219. Theory of klinostat, grass-haulms. 220. Do., Cucurbita. 221. Diageotropism, roots. 222. Growth of secondary roots in light. 223. Diageotropism, Narcissus. 224, Horizontal branches. 225. Torsion of internodes. 226. Budsoftheyew. 227. Epinasty. 228. Epinasty and geotropism. 229. Nutation of epicotyls , pp. 168—183.

Chapter VIII. Further Experiments On Movement

Section A. Stimulus of contact, chemical agency, moisture, ehanges in illumination and temperature. 230. Tendrils, sensitive to contact. 231. Tendrils, De Vries’ injection experiment.

xii CONTENTS.

232. Tendrils, Pfeffer’s contact experiment, 233. Mimosa, movements produced by stimulation. 284. Mimosa, temperature. 235. Mi- ‘mosa, darkness. 236. Mimosa, continued stimulation. 237. Ovalis acetosella, sensitiveness. 238. Oxalis, Briicke’s experiment. 239. Drosera, stimulated by meat and by inorganic matter. 240. Drosera stimulated by dilute solutions. 241. Drosera, inflection indirectly causes. 242. Berberis, irritable stamens. 243. Berberis, effect of chloroform. 244. Stigma of Mimulus. 245. Centaurea, irritable stamens. 246. Phycomyces, curvature towardsiron. 247. Hydrotropism. 248. Movement of chloroplasts. 249. Chemotaxis, antherozoids. 250. Opening and closing of tulip, temperature. 251. Tulip, sensitive to small change of temperature. 252. Crocus, mechanism of movement. 253. Light and darkness, daisy. 254. Light: and darkness, Trifolium. 255. Nyctitropic movements, Trifolium, 256. Do., Mimosa, self-recorded. 257. Paraheliotropism, Averrhoa.

Section B. Autonomous movements. Periodicity. 258. Cir. ecumuutation. 259. Do., twining plants. 260. Autonomous movements, Trifolium. 261. Do., Averrhoa. 262. Do., Desmodium. 263. Periodicity, light and darkness, daisy. 264. Perio-., dicity, temperature, daisy. 265. Contrast, daisy pp. 209—216.

Chapter IX

INTRODUCTION. SOLVENTS. METHODS OF EXTRACTION. GENERAL NOTES ON APPARATUS AND MANIPULATION.

Introductory. Preparation of material to be examined. Preparation of extracts: non-nitrogenous plastic substances. Preparation of extracts: nitrogenous plastic substances. Filtration. Evaporation of solutions. Changes occurring in solutions on keeping pp. 221230.

CONTENTS, xiii

Chapter X

PROTEIDS. AMIDES. AMMONIA, NITRATES, &C.

Literature. Practical classification of nitrogenous plastic, substances. Qualitative examination for proteids insoluble in ‘water, soluble in dilute alkali—for proteids soluble in water—for peptones and albumoses—for amides—for ammonia, nitrates, nitrites. Estimation of proteids—of peptones and albumoses. Estimation of amides. Estimation of ammonia, nitrates and nitrites. Experiments on nitrogenous metabolism. Qualitative examination of Onobrychis sativa for proteids &c. Comparison of amounts of proteids, peptones, amides in seeds of Onobrychis and in shoots of the same grown under various conditions. Comparison of amounts of ammonia, nitrates, nitrites in shoots of Onobrychis from plants variously treated . : pp. 231—242.

Chapter XI

OILS AND FATS. GLYCERIN.

Literature. Extraction of oils and fats. Qualitative examination of benzene extract. Reactions of glycerin. Quantitative examination. Determination of total oils and fats—of free fatty -acids—of glycerin. Experiments. Determination of oils and fats in seeds of Lepidium— in seedlings of Lepidium, young and old . 5 Fi pp. 248—247.

Chapter XII. Tannins And Glucosides

Literature. Extraction of tannins and glucosides. Many different bodies included under heading tannin and glucoside. Qualitative tests for tannins. Qualitative tests for phloroglucin. Removal of tannins. before examining for sugars. Determination of whether « tannin is a glucoside or not. Glucosides, Identification of salicin. Examination for certain sugars. Experiments. Testing extract of willow-bark for tannin, salicin, sugars. Estimation of certain sugars in young and old fruits of Musa sapientum . ‘ 3 - : . pp. 248—257.

XIV CONTENTS.

CHAPTER XITI.

DEXTRINS AND SUGARS, GLUCOSES, CANE-SUGAR, MALTOSE, &¢,

Literature. Soluble carbohydrates. Qualitative test for fermentable sugars. Estimation of fermentable sugars. Removal of dextrins. Tests for glucoses, cane-sugar, maltose, mannite, pentoses. Estimation of glucoses, cane-sugar, maltose. Calculation of results. Experiments on sugars. Testing leaves of Tropgolum majus for various sugars. Estimation of fermentable sugars in leaves and roots of Beta vulgaris. Estima. tion of various sugars in leaves of Beta vulgaris under different conditions,

Chapter XIV

STARCH. CELLULOSE.

Literature. Estimation of starch and cellulose. Experiments on starch. Estimation of starch in the potato by different processes— in leaves of Acer pseudo-platanus under different conditions. In grains of wheat before and after germination ss 3 fs pp. 272—276,

Chapter XV. Organic Acids And Salts

Literature of organic acids. Qualitative examination for organic acids, Determination of ‘acidity’ of extracts. Literature of inorganic salts. Preparation of ash of tissues. The constituents of the ash. Estimation of chlorine—phosphoric acid—alkalies—in ash. Estimation of calcium oxalate in tissues. Experiments on organic acids. Comparison of acidity of juice from old and young rhubarb petioles—of acidity and amounts of sugars in juice from ripe and unripe apples. Experiments on inorganic salts. Weights of ash from normal and etiolated leaves. Estimation of phosphoric acid and alkalies in leaves and grains: of barley—of calcium oxalate in young and old leaves of Sempervivum: tectorum . . . . . . . . . pp. 277 —284,

CONTENTS. XV

Chapter XVI. Unorganised Ferments. (enzymes.)

Literature. Extraction of enzymes. Comparison of activity of extracts. Experiments on diastatic ferments. Preparation of solid diastase. Influence of filtration on diastatic power of extracts. Comparison of diastatic power of malt and ungerminated barley—of leaves of Pisum sativum and Trifolium pratense. Experiments on invertase and glycase. Decomposition of « glucoside (salicin) by an enzyme (synaptase) from another plant ‘ ; 7 ‘ pp. 285— 293.

Chapter XVII. General Experiments

The increase in weight of growing Spirogyra. The influence of inorganic salts on the formation -of starch, The changes in the reserve materials of an oily seed during germination under different conditions.

APPENDIX I.

Notes on the results likely to be obtained in experiments on metabolism . . . ‘ : - : : . 5 pp. 296—S04. APPENDIX II.

List of reagents and material required for experiments on metabolism ... a2 8 ‘ ‘ . . F pp. 305—308.

FIG,

LIST OF ILLUSTRATIONS.

Apparatus for demonstrating respiration .

Apparatus for estimating CO, produced during caapiratton

Foil clamp for holding cover-slips together under water, for use with Velten’s hot-stage : : . -

Apparatus for the preparation of mien free from CO, it not free from oxygen . é . . . .

Arrangement for the culture of a in an atmosphere thee from CO, . . $ : < 3

Apparatus for gananulpes for use in experiments on assimilation .

7, 8,9 Winklesttempal apatite for gas- -amelyate F 10,104 Lemna cultivated in various nutrient solutions .

11 12 13

14 15

17 18

Apparatus for demonstrating root pressure . 5 . F

Another apparatus for the same purpose .

The Potometer, for estimating the absorption of water bya a cut branch . : A é . 2

A modification of Kohl’s aipumtne for ‘th same purpose .

A method of preventing evaporation from the surface of a flower-pot . c : .

Apparatus for comparing _ ia ieciepinalion with the sehen absorbed . . ‘

A spring-balance for use in eanentcation expetinenta.

A hygrometer made of the awn of Stipa for performing Garreau’s experiment . . 5‘ ‘ é r :

Devaux’s gelatine method of making an air-tight sanetion with the petiole of a leaf . . :

Apparatus for demonstrating the ligeroasopis meeperiee of the awn of Stipa 3 2 ‘ f

LIST OF ILLUSTRATIONS.

Diagram illustrating the use of turgescent tissue in De Vries’ experiments on isotonic coefficients .,

Tracings from split portions of the hypocotyl of Ricinus ea in experiments on isotonic coefficients . 2 :

Pfeffer’s gypsum method

Arrangement for demonstrating that Lagpeeeu ost ise rigidity when bent . ‘ <

Micrometer-screw used in growth aupertneuts

Recording auxanometer .

Method of using the necdnomiidedayee

Tracing illustrating the effect of an increase of teunpoentiatd on growth

Hanging writer for veconting: geonnepie. or thay movements on a revolving drum .

Illustrating the curvature of a oot whieh — weeerreradl front the effects of decapitation .

Curvature of roots produced i small planes of easd attadhed to the tips . ‘ . s 3

Drooping of laurel leaves in a frost

A twig of Veronica salicifolia exposed to oblique flhunitantion

The klinostat . 4 2

Section showing part of the mechan of he idingetat

A seedling Cucurbita which has germinated on the klinostat ; showing the frill-like growth of the heel or peg

Diageotropism of the flower of Narcissus poeticus

The twisted internodes of Lonicera :

Leaves of clover in the day and night nositiod -

The sleep-movements of Mimosa recorded on a drum by means of a hanging writer

Paraheliotropic movement in Averrhoa Dilimbi ‘

Diagram representing the circumnutation of a cabbageseedling i ‘ * 6

Apparatus for distillation ides vediaged pressure .

Xvii PAGE 115

116 120

127 138 141 145

147 158 160

162 164 169 171 172

177 179 181 204

206 207

211 228

ADDENDA AND CORRIGENDA.

Page 1, line 4 for ‘‘ grow-” read ‘‘ growth-’’- » 68, line 14 for “developement” read “ development.”

» 120, Fig. 23 is copied from Pfeffer’s paper in Abhandl, k. Stichs Ges. Band xx. 1893.

» 121, line 8 for ‘‘silk-paper” read ‘“‘ tissue-paper ”.

» 188, 141, Figs. 25 and 26 are from the Catalogue of the Cambridge Scientific Instrument Company.

PART I.

GENERAL PHYSIOLOGY.

Chapter I. On Some Of The Conditions Affecting The Life Of Plants

Section A. Respiration. Suction B. Temperature— Poisons — Electricity.

Section A. Respiration.

The presence of free oxygen is a necessary condition of the life of all the higher plants. This fact will be more conveniently demonstrated in the chapters on growth and grow-curvatures. The present section is intended as an introduction to the study of the facts without special reference to the importance of respiration.

(1) Take a stoppered jar of about 500 c.c. capacity, fill it to one-third of its. height with horse-chestnut buds (in spring) or with beans (in winter) which have been soaked in water for 12 hours and have been afterwards placed in damp cocoa-fibre for 12 hours. Place the jar in a warm, dark room, and after 12 hours cautiously open the jar and lower a lighted taper which will be extinguished as it enters the CO, produced.

D. A.

2 RESPIRATION. [cH. 1

(2) Take a filtering flask of 400 or 500 cc. capacity, having a lateral opening as shown in fig. 1 to which a glass tube, A, (4 or 5mm. bore) is attached by thick rubber tubing and wire ties. The end of A dips into the mercury in the beaker Hg. The flask contains enough

CH. I] RESPIRATION. 3 germinating barley to cover a piece of wet filter paper at the bottom of the flask. Barley germinates well in winter: it should be soaked in water for 24 hours and kept in damp air for 24 hours before use. A test-tube T half full of strong KHO is introduced into the flask, which is then closed by a sound tightly fitting rubber cork, As the CO,, produced by respiration, is absorbed by the KHO, the mercury in the beaker Hg is sucked up the tube A. In starting the experiment it is necessary to warm the air in the flask before the end of A is forced into the Hg, so that as the air cools again the mercury may be sucked a little way up the tube to a point which will then serve as zero for subsequent observations. The warming may be done by immersing the flask in water at

40° for a few minutes; or it may be warmed by the hands.

(3) Sachs’ method?.

Place 10 germinating beans in a jar A, fig. 2, closed by an india-rubber cork pierced by two holes and fitted with glass tubes. One tube is connected with an aspirator so that a current of air is drawn through the vessel and keeps up continuous normal respiration. The other tube serves to admit to the flask air free from CO,; for this purpose it is connected with a filtering bottle F containing a few sticks of KHO. The air is admitted to F through a tube 7 filled with soda-lime. In order that it may be certain that no extraneous CO, enters the

1 Physiologie Végétale (French Translation), 1868, p. 295, fig. 35. Also Pfeffer’s Physiologie, 1. p. 349, fig. 38. 1—2

4 | RESPIRATION. [cH. 1 flask, another washing bottle B containing baryta water is fitted between F and the experimental flask, A. The drop-aspirator figured by Detmer’ answers very well, it is made from a distillation tube and is attached to a tap through which a current of water in detached drops passes, and produces a correspondingly slow suctioncurrent of air at the side tube (c in Detmer’s figure); The outflow tube. should be about 2 feet in length to insure that the suction is strong enough. In the absence of a drop-aspirator the current may be moderated as Sachs recommends by allowing the air to enter the first washing bottle through a fine capillary tube. If the sink in the laboratory is inconveniently placed. the

1 Praktikum, p. 179, fig. 76.

CH. I] RESPIRATION. 5 air suction may be carried to any part of the room by means of fine lead-tubing.

Between the flask and the aspirator two washing bottles P, C, containing baryta water are fitted in which the CO, produced by respiration of the plants is caught and precipitated as BaCO,.

The amount of the precipitate may be estimated by titration, for which see Sutton, Volumetric Analysis, 5th Ed. pp. 80—89.

(4) Intramolecular respiration.

To demonstrate the fact, the following simple form of experiment may be tried.

Soak 6 peas in water for 12 hours, when the seedcoats can easily be removed without injury to the embryo; the removal of the testa is necessary to avoid introducing air with the peas, the object of the experiment being to show that CO, is produced in the absence of free oxygen. Fill a test-tube with mercury and invert it in a mercury trough which should stand in a strong wooden tray. This precaution is advisable in all experiments involving the use of mercury, so that if any accident occurs the mercury may not escape and get into the cracks of the floor. It is desirable to use clean mercury which has been redistilled, but the experiment will succeed perfectly without any special care being taken in its treatment.

Pass the peeled peas one at a time under the rim of the test-tube so that they float up into the mercury, and occupy the upper end of the test-tube. On the following day it will be found that the test-tube is half full of gas,

6 RESPIRATION. [CH. I and the peas are therefore clearly visible, instead of being partly hidden by mercury.

A few drops of water are now passed in under the test-tube rim with a bent pipette, and a fragment of caustic potash added from below, in this way a strong solution of KHO is supplied, by which the CO, is absorbed.

(5) Another method.

The Torricellian vacuum was used by Wortmann in his work on intramolecular respiration’. A tube closed at one end, and of greater length than the height of the barometric column, is filled with, and inverted over mercury. Three or four peas are floated into the vacuum at the top of the tube. After 24 hours a depression of several cm. will be observed in the height of the column, which will rise to nearly its original level on the addition of KHO.

(6) Pfeffer’s method.

‘To get -accurate results another method must be followed ; the following is taken from Pfeffer’s paper in his Tiibingen Untersuchungen, Vol. 1. p. 637.

The principle is that already described for estimating ordinary respiration, but instead of air, a current of hydrogen is drawn through the vessel in which the plants are contained. It is necessary to prevent the entrance of extraneous CO, and to make sure that the hydrogen has no admixture of oxygen.

1 Sachs’ Arbeiten, u. p. 500.

CH. I] RISE OF TEMPERATURE. 7

(7) Rise of Temperature.

The spadix of an Arum is the classical material for demonstrating the heat produced by respiration in plants. We have used the British Arum maculatum, but for some reason the experiment has not always succeeded. Remove the spathe from 4 or 5 spadices (of which the spathes are just beginning to expand) and fix their stalks in wet sand, so that the specimens stand vertically in a ring. Suspend a delicate thermometer in such a way that the bulb falls among the Arums, and wrap them round with a flock of cotton wool so that they may touch the bulb. Kraus+ has shown that the respiration of Arums is easily affected by any injury to the surface of the spadix, the specimens must therefore be delicately handled. Hang a second thermometer (which must be previously compared with the first) close to the Arums, and cover all with a bell-jar standing in water. The bell-jar is necessary to prevent currents of air.

(8) Rise of temperature.

The following is Sachs’ arrangement for showing the rise of temperature in germinating peas”. We have found flowers, such as those of dandelions, treated in the same way to answer well. Gather a large handful of dandelion flowers* cutting the stalks just below the head, place them in a large funnel supported in a beaker half-filled with KHO. Hang a thermometer so that the bulb is

1G, Kraus, Naturforsch. Ges. Halle, xv1. 1884.

2 Sachs’ Text-book, Hd. u. p. 724. Fig. 472.

3 Or in winter of young flowers and buds of a small-flowered Chrysanthemum.

8 OILY SEEDS. [CH. I covered by the flowers, and let the control thermometer be supported in a funnel containing coarse sawdust slightly moistened and loosely packed. This arrangement is meant to equalise the conditions of the two thermometers, and to prevent the bulb among the flowers acting as a wetbulb. We find, with the control thermometer hanging simply in the air, that the flowers keep about 2° C. above the control temperature, As before, the whole must be covered with a bell-jar. Sachs uses a tubulated bell of which the opening is plugged with cotton-wool.

(9) Oxygen necessary.

Several of the earlier observers have shown that when the air is replaced by indifferent gas the tempera-_ ture falls. Pfeffer! recommends that the germinating seeds or other material should be placed in a glass balloon having three apertures—one of which serves for a thermometer. When the temperature of the respiring material has been proved to be steadily above that of the surrounding air, the atmosphere in the balloon is replaced by hydrogen, for which purpose the two lateral apertures will serve, The readings of the two thermometers should now become practically equal, and it should be possible to re-establish the difference by readmitting air.

(10) Germination of oily seeds,

Repeat experiment 2, using oily seeds for the germinating material, and omitting the test-tube of KHO. Hemp seeds will serve the purpose: they should not be

1 See Pfeffer, Physiologie, u.p, 408. Fig. 40.

CH. I] SUCCULENTS. 9 soaked in water before they are used, but placed air-dry on wet filter paper in the flask.

The mercury rises in the tube in spite of the absence of KHO. As a control experiment an equal weight of barley should be placed in precisely similar conditions. In our experiments the column of mercury was depressed in the case of the barley.

The two flasks should be kept as nearly as possible at a constant temperature; for an accurate determination of the results, barometer readings must be taken at the beginning and end of the experiment, and corresponding corrections must be made. But any external influences will affect the experimental and the control flask equally, so that the difference between their readings must depend on the different behaviour of the seeds in germination.

(11) Succulents}.

In certain succulents an increase of the acidity of the cell sap is accompanied by a fixation of oxygen. Therefore, when the plant is placed in the apparatus used in experiment 10, a rise of the mercury takes place. The following is taken from Detmer, p. 224,

He recommends Rochea falcata as especially good for the experiment. A leaf is taken from the plant at the close of a hot summer day, cut into pieces and introduced into the eudiometer (Detmer, fig. 14). The lower end of the graduated tube is placed in water and the apparatus kept in the dark until the following morning when a considerable rise in the water column is visible. As a

1 See De Saussure, Recherches Chimique. (An. xii=1804), p. 65.

10 INJURIOUS TEMPERATURES. (cH. I control a similar eudiometer is fitted up with non-succulents, such as pieces of young sunflower’.

Section B. The effect of various temperatures : of certain poisons: and of electrical shock.

To get a rough idea of the upper limit of temperature which ordinary plants can endure, it is best to make a few simple experiments with plants in which the moment of death is marked by some obvious change, e.g. in colour. Ozxalis acetosella is useful for this purpose, because death is indicated by a dingy yellow colour due to the action of the acid cell-sap on the chlorophyll.

Fill a beaker with water at 25°C., and suspend in it a thermometer, to the bulb of which a leaf of Oxalis is attached. Heat the water by means of a gas flame, and note the temperature at which the leaf loses its fresh green tint.

Ifthe Oxalis leaf is injected with water before the experiment, it changes colour at a temperature several degrees. lower than in (12). This is a simple way of demonstrating | the fact given by Sachs (Physiologie Végétale, p. 71) that plants in air endure a temperature which they cannot bear in water.

The cells of the injected Oxalis leaf acquire the tem-