a Pat TRE Sen ATER TNS MTS RNR SE Rhea phat nets NR ain RUTH Siete ath stat, Pacey ra yt Bagel Rene aia hers SR onan MRAM Hoty (seer a Ua nninotae 7 Aenean ead dra Bees GAC ae ata iat pel ey Ror ihe ey f A AREAL G ee pra et UA i r eng ie BEN, PAE RELA OA een Petes AAA te MARAE dinar ire a a aes , Aas ea A rAd i eer RAY t sei ey if Atty RACHA Ra RA f SES MR AEE) ARREST LANs Tusa : hea ee tne Read Aas oe ee a et eae ee bts 5 ' a r ert ee ed TaD AAI NHEG a OG S4 Oe Bes eg EOE E A ae a Ae RE Or dg Ree ey Cie) ass re pane CO BAREIS ey EMA AH au i Raha eI Md i Agi ay ere bape. 4 Pad if sf r Ag rs 1a eet ere! aes Fh hen, Cee Ae aNd oe fe Ai td tae Wetter esp yn eae i ees ESA REE aad SARCR Pre re et AeA RMA yl yap Pt Fy te es MALU RAG Tae an i reste CA ag oe “OZ 699 000 Ve6l € en 6S9°€Z8 NO Aseaqyy Ayssaaiuy jausod THE DEPENDENCE OF GROWTH UPON TRANSPIRATION UNDER DIFFERENT CONDITIONS OF HUMIDITY MINOR THESZS Presented to the DEPARTMENT OF BOTANY Foy the Desreée of MASTER OF SCIENCE IN AGRICULTURE By Charles Frederick Clark, B. 5S. Cornell University June, 1907 THE DEPENDENCE OF GROWTH UPON TRANSPIRATION UNDER DIFFERENT CONDITIONS OF HUMIDITY. The phenomenon of growth is one of great complexity it being the resultant of several processes which are carried on within the plant, the several factors concerned with it being in turn influenced to a greater or less de- gree by external conditions. The relation of one of these processes, transpiration, to growth has given rise to mich discussion among plant physiologists and is still an unsettled question. Among those who look wpon transpiration as primarily a vital process there are three general views held regard- ing its role : (1) To enable the plant to take um a suffic- ient supoly of mineral salts ; (2) To prevent high temper- atures in the plant ; (3) That it is a necessary evil, necessary in that moist membranes must be exposed for the exchange of gases and at the same time an evil since such large quantities of water are required. Strasburger, Woll, Sehenk and Sehimper (12) hold that <-the plants would be unable to obtain a sufficient supply of nutrient salts if they took up only as much water as they could retain and make use of. They also consider transpiration necessary to secure a proper concentration of those salts. Pfeffer (9) regards transpiration essential for the distribution of mineral salts in the plant and even main- tains that srovth varies with the transpiration. Iie alse thinks it probable that transpiration influences the ex- change of gases. If it were not for transpitation, the intercellular spaces would become filled with water which would prevent aeration of the tissues thus retarding meta- bolism and growth. On the other hand, in the presence of a limited supply of vater in the plant, the diminution of transpiration must of necessity interfere with the free ex- change of gases thus inhibiting the assimilation of CQ. Sachs (10) in commenting woon the fact that assimila-— tion may be carried on in land plants which are surrounded by a saturated atmosphere, points out that the assimilation in this case is extremely feeble and furthermore that even under these conditions transpiration may occur to a slight degree and a feeble flow of water maintained. Edmond Gain (2) concludes from the works of Hellriegel Haberlandt, Wollny and others that a certain relation exists between the amount of dry matter elaborated and the weight of water transpired by the plants during vegeta- tion. This view is also held by Lawes and Gilbert (7). Green (4), in addition to the view that transpiration is necessary in order that the leaves may be supplied with inorganic salts, maintains that it is imperative in order to prevent a rise of temperature to a point which would be fatal to the plant. He states that the amount of radiant energy taken up by the leaves has been computed to be near- ly 50 times the amount which can be utilized in the process of photosynthesis ; if the heat were allowed to sameaees in the leaf unchecked it has been calculated that its tem- perature would rise during bright sunshine more than 12° C. per minute. Pfeffer (9) and Tschaplovitz (18) also recognize the probability of a regulatory influence of transpiration upon the temperature of the plant. Kreusler (6, See VYoods, 15), does not regard the check- ing of transpiration by a complete saturation of the at- mosvhere as unfavorable to assimilation but, on the other hand, holds that assimilation may be reduced by a dry at- mosphere, which is conducive to excessive transpiration, long before the turgescence of the leaf is visibly diminished. Barnes (1) advances the theory that the amount of Salts absorbed is dependent unon the living cortex of the rootlets and the mesophyll of the leaves. He states, "it. the cortex be freely permeable equilibrium in the distri- bution of any given salt will occur, assuming for a time no evaporation from the serial parts. If then evaporation concentrates the solution the higher diffusion tension of thet salt will tend to drive it to those regions where the diffusion tension is lower. This tendeney, therefore, “would operate against the further supply of that material in the leaves. If the cortical layers be not freely per meable, the amount absorbed is regulated wholly by proto— plasmic activity and cannot be affected directly by outside supply. The phenomena of selective absorption show that transpiration does not determine in those cases the amount of salts absorbed." The experiments conducted by certain investigators serve to indicate that an increase or decrease in trans-— piration, as influenced by the humidity of the atmosphere, does not necessarily produce a corresponding increase or decrease in growth. ce ) Godlewski (8) found that a sudden in inerease or de- crease in humidity produced a corresvonding change in growth which, however, was only transitory. At the end of one-half hour it returned to its former rate. Thies led him to the conelusion that the action of humidity vas not to change growth but to produce a change of turgescence and consequently tursger—distension. Sechlésing (11), working with tobacco plants, found that transpiration was greatly decreased by a moist atmos— phere while the gain in dry substance was increased, the plants in the moist atmosphere gaining 5.2 grams per liter of water evaporated as against 1.2 grams in the dry atmos- phere. The composition of dry matter was also found to vary under the different conditions of humidity, the per centage of ash being 18 in the moist atmosphere and 21.8 in the dry. In commenting upon this fact, Schlosing states that all tobacco plants of any source, species or degree of development, examined by him, have given in the vicinity of 20% of ash, hence the plants grown under humid conditions were abnormal in this respect. Woliny (14) found that the dry weight and total amount find that the quantity of water transpired by some of our common field crops during their period of growth is not a measure of the amount of dry matter formed. That the ratio between these quantities is not constant is shown by the following table which gives the amount of water trans- pired per unit of dry matter, as determined by different investigators. TABLE 1. Lays and. Gilbert Hellriegel Wolliny King Wheat B29 | £59 _- = Barley 262 e1LG 393 774 Oats - 402 557 665 Red Clover 249 ‘ 8380 4538 - Peas 235 292 477 4497 In commenting on these results, Hall (5) says, "Phe divergencies in these results are intelligible if we con- sider that the transpiration process by which the vater is lost and the assimilation process by which the plant gets heavier have no necessary connection, the both become active under the same stimuli of light and varmth." The numerous modifications of desert plants for the purpose of reducing transviration have been considered by some as evidence that this process is not essential to the growth of plants. It must be borne in mind, however, that under these conditions transpiration is still carried on to some extent, furthermore, the conditions are so faveraple for excessive transviration, that were it not for these special adaptations the plants would soon be deprived of their limited supply of vater. The exneriments described on the following pages were undertaken with a view toward determining what relation, if any, exists between transpiration and srovth under aiffer— ent conditions of humidity. Five svecies of plants vere employed for this purpose, viz., corn (State Flint), sunflowers, peas, wheat (Dawson's Golden Chaff) and buckwheat. The plants were grorn in wire baskets 3 inches in dia- meter and © inehes deep. The manner of preparation was as follows : The tops of the baskets were first dipped in melted paraffin to the depth of about one inch. This formed a collar around the top which prevented the paraffin from flowing over the surface of the soil while the remain- der of the basket vas being coated after filling. It also prevented the water which was added from time to time during the experiment from flowing off at the sides of the. basket. The baskets vere filled within three-fourths of an inch of the top with soil which had been thoroly mixed, pulverized, and screened to remove the lumps and stones. They were then dipped in paraffin until coated sufficient- ly to prevent loss of water. The paraffin also served to cement the soil particles on the outer portion of the soil cokumn to the sides of the basket, thus preventing the formation of an air sovace between the soil and basket. The seeds were soaked in water before planting until germination had commenced. This method of treatment hast- ened germination and also enabled a selection to be made of seeds which were of nearly uniform vigor, thus eclimina- ting to some extent extremes of individual variation. A few more seeds were planted than the mumber of plants re- quired. This permitted another selection to be made after the plants had begun to grow. When the plants were 2 to 21/2 inehes in height, they were thinned to the required 10 number and the tops of the baskets sealed to prevent evap- Oration from the surface of the soil. This vas done as follows : A circular piece of paper having a diameter a little less than that of the basket was dipped in paraffin and a slit of sufficient length and width to admit the young plants vas cut into it. Previous to sealing a layer of fine sand, about one-fourth ineh in thickness, was added to each of the baskets to aid in preventing evapora- tion from the surface of the soil. The paper vas then adjusted and fastened in place by running melted paraffin around the edge, thus cementing it to the sides of the basket. The amount of paraffin added vas determined by veigh- ing the baskets before and after sealing. The difference added to the weight at planting gave the final ee i.e., the weight of the paraffin and basket plus that of the soil in which the moisture content had, by the addition of vater, been brot up to the amount considered to be most favorable for the growth of plants. The loss of vater by transpiration was determined by weighing the baskets at intervals of three or four days. iz Water was added at this time until the weignt of the basket was a few grams above the optimum, the excess depending upon the rate of loss. The plants were divided into three lots and each sub- jected to one of the three conditions, which vere designa— ted as dry, check and moist. The three lots were Placed sate side in the greenhouse, the dry and moist being under bell-jars while the check was un#nclosed. The average relative humidity of the dry was 78°, of the check 88°and of the moist 98°. The excess of moisture was removed from the atmosphere of the dry, by placing calcium chloride in onen dishes under bell-jars. The calelum chloride was changed as soon as it had become sat- urated with moisture, usually morning and night. The high degree of humidity of the moist bell-jars was maintained by placing pieces of wet filter paver under them. The soniodead mere aerated each morning in the fol- lowing manner : With those subjected to the dry conditions this was accomplished by forcing air, from which the moist- ure had been removed by passing thru a column of calcium chloride and pumice stone, into the bell-jars. In the ease of those in which the moist conditions obtained, the bE air was changed by removing the bell-jars for a few minv- tes. This was done at a time when the mmidity of the atmosphere in the greenhouse was relatively high. The temperature of the three conditions was the same as that in the open greenhouse, viz., about 65°F. during the day and 60°F, at night, ex2e>t that on bright, clear days the rays of sunlight caused a rise in temperature of several degrees in the bell-jars above that in the open greenhouses This change of temperature vas the same in both the dry and moist. The temperature factor must be taken into consideration when comparing the eheck with the other two conditions. The folloving table gives the number of baskets used, the mumber of plants in each and the date of the beginning and end of the period during which transpiration records were taken. 12 Table II. Kind of No.of No.of Beginning of End of Plant baskets plants in trans. period trans. period. each. Corn --- 12 --- 2 --- Feb. 2 --- Feb. 22 Sunflowers 9 --- 2 --- Feb. 2 -- Mar. 2 Peas --- 9 --= 2in 6 Feb. 17 --- Mar. 7 8 in 38 Wheat ---9 --- G --- Mar. 5 --- Mar. 23 Buckwheat 15 -- 4 --- Mar. 19 Apr. 5. At the close of each part of the experiment, which was on the date indicated in the last column of Table II, the plants were cut ai the surface of the soil, measured, the green weight, dry veight and ash determined, aiso the ratio between the water transpired and the dry matter pro- ducede The results are given in the following table : 14 Table III. Av. Green Dry % % Water ht. weight matter dm. Ash ash Trans. transp. ams ens. fT1S » gms. in ems. per am. dete eM. mse corn — Dry 42.2 35.0 1.9630 7.385 .3405 17.35 380.0 1938.6 Creck 39.2 25.4 LsBll7 7cl15 228227 17.675 180.9 99.5 Moist 389.9 27.0 1.8352 6.80 .2274 18.38 123.9 67.5 Sunflower Dry . 29.9 19.6560 1.6140 8.21 .3878 24.02 G15.0 381.66 Check 24.5 16.7638 1.3115 7.28 .2910 24.92 348.4 287.58 Moist 25.6 15.0080 .8565 5.71 .2295 26.80 110.2 128.66 Peas- to ww Co Ci Dry 40.2 Qe: » 79928 8.65 .1178 14.74 227.3 284.41 Check 387.0 9.0737 .74065 &.16 .1071 14.46 154.9 209.10 Moist 42.9 9.7130x% .9145 99.42.1144 12.51 46.4 50.74 wheat - Dry 32.2 6.1905 .8543 13.81 .1300 15.21 302.6 354.00 Check 23.4 4.3537 .6397 15.84 .0794 11.51 155.9 226.04 Moist 33.0 7.6445 -9665. 12.64 .19835 13.381. 95.4 98.71 Buckwheat - Dry 17.8 10.5875 .9720 98.18 .1682 17.30 299.8 208.44 Check 14.1 6.68035 .6345 9.61 .1110 17.50 159.3 951.07 Moist 28.6 10.6190 .9315 8.77 .1625 17.44 122.4 131.40 xe Figures too lor. The plants wilted very rapidly as soon as removed from the moist atmosphere thus reducing the weight. Ze Figures too high. Same reason as above. Should be less than figures for "dry". Le An inspection of this table shows that height, tobal weight and composition are influenced to a greater or less degree by the amount of water transpired, the direction and extent of this influence varying with the species. It will be noted that in the first two series the re- sults for the checks are, in general, intermediate between those of the dry and moist, while in the case of peas, wheat and buckwheat the results are lower than those ob-— tained under either of the other two conditions. This is attributed to the fact that the three last series, named vere run later in the season (see table II) when the number of hours of sunshine per day was greater, as vas also the number of bright, clear days. The effect of this was to eause a rise of temperature in the bell-jars above that of the air surrounding the check plants. Since we have an- other factor entering into the problem which exerts a con- Siderable influence on growth, the results obtained from the checks are not comparable with those obtained under the other conditions, hence they will be omitted from the present discussion. With the exception of the sunflowers the plants appeared to suffer no ill effects from either the ary or 16 moist atmospheres. In the instances referred to the Plants growing in the atmosphere saturated with moisture were more or less distorted, the stems being somewhat Knotted or twisted. “eS probable that the excessive strain due to thé inerease in turgor, as a result of the checking of transpiration, caused the tissues to assume somewhat abnormal shapes. There TAS A preceptible difference in the height of the plants grown under the two conditions as is shown by the figures in table IIT. Corn and sunflowers reached their greatest height in the dry atmosphere, while peas, wheat and buckwheat were taller where moist conditions pre- vailed. The inerease in height was in every instance coincident with an increase in total dry matter except in the case of buckwheat. with the exception of corn this game relation exists between the height and green weight. It will be seen that the amount of water transpired exerted a marked influence on the composition of the plants. In every instance the percentage of water was greater in the plants grown in the moist atmosphere. We woulda expect this to be the case as the turgidity of the 17 cells, and consequently the amount of rater contained in the tissues, would be much greater where there was but little loss by transpiration. The percentage of ash in dry matter also varied in the plants grown under the diff- erent conditions. It is significant to note that in every instance, com- paring the plants grown under dry and moist conditions, the higher percentage of ash in dry matter is coincident with a lower yield of total dry matter, tho the total amounts of ash constituents are practically the same under both conditions. This appears to indicate that the con- Aitions which are unfavorable for growth inhibit the elab- oration of organic food substances to a greater degree than the absoprtion of mineral salts. It will be observed that transpiration was not en- tirely checked in the moist atmosphere. This is in accor dance with the view generally heid by plant physiologists that, in the presence of sunlight, the temperature of the plant usually rises ebove that of the surrounding air and that under these conditions transpiration may be carried on to a Slight degree even in an atmosrhere saturated with moisture. 18 In the case of corn and wheat, more particularly the latter, part of the water recorded under the head of trans- piration was removed from the slants by guttation. During their early period of growth drons of water were often seen, in the morning, on the ends of the leaves of those plants which were in the moist atmosphere. Toward the latter vart of the experiment this was not noticed. The results show very conclusively that transpiration varies directly with the humidity of the atmosphere sur- rounding the plants, but growth, however, does not appear to show a similar relationship to either of these factors, in fact the largest total yield of dry matter in three cases out of five was where the least quantity of water was transpired. If srovmth were directly dependent upon transpiration, as many of the leading plant physiologists assert, then we would exvect to find, for each species, a constant ratio between the increase in substance ana the water transpired but sueh is not the case, as is shown in the last colum of Table III and by the results of experiments conducted along this line by certain investigators. 19 Conclusions. The results shovy that in certain of the species of plants under investigation maximum growth may be carried om wnen transpiration if reduced to a minimm, at least during the early period of vegetative growth. Where there is a decrease in growth coincident with a checking of transpiration the decrease appears to be due to the inhibition of the elaboration of organic matter rather than by limiting the quantity of mineral salts absorbed. In general the checking of transpiration does not avoear to decrease the total amount of mineral salts ab- sorbed vy the plant, at least for the »~eriod of growth auring which the plants were under observation. Tne composition of the plant is matertlally affected by vestepinne in the rate of transpiration, especially the percentages of moisture in the fresh plant and of ash in the dry matter. There appears to be no constant ratio between the quantity of dry matter produced and the amount of water transpired, the relation varying according to the envir- 20 onment of the plant. This vork was carried on under the direction of Professor G. F. Atkinson and lir. o. . Edgerton, to whom I am indebted for many valuable suggestions. Be Be 4. 5e al Bibliography. Barnes, C. nH. The Significance of Transpiration. Science N. 6,15 : 460, 1902. Gain, Edmond. Le role vhysiologique de l'ean dans la vegetation. Ann. des Sei. Nat., 7% ser. 20: 63-213. 1895. Godlewski, T. Studien ueber das Wachsthum der Pflanzen. Bot. Centpl., §5 : 44 - 40, 1893. Green, J. Reynolds. Vegetable Physiclogy, 324, 825. 1900. Hall, A. D. The Soil, 84, 85. 1903. Kreusler, U. Ueber eine Methode zur Beobachtung der Assimilation und Athmung der Pflanzen und ein- ige diese Vorgaenge beeinflussende Momente. Tagebl. der Naturforscher - Versammlung zur Strassburg, 539. 1885. 22 7. Lawes, J.B., and Gilbert, J. H. Influence de la secheresse de 1870 sur les recoltes de Rothamsted. Anne Agron., I. 251- 278. 1875. 8. Livingstone, B.%. The Relaticn of Transpiration to Growth in Wheat. Bot. Gaze, 30: 178 - 195. 1905. The nelation of Transnviration to Other Pune- G1Gnss Ness 5 i6 : 619. 1905. The Relation of Desert Plants to Soil Moisture and to Evaporation. Carnegie Institution of Washington, Publication No. 50 ; 41. 1906. 96 Pfeffer, JW. The Physiology of Plants, (English translation by Asds Mweart) I : 284, 285. 1900 5 FI : 186, 1908. 10. Sachs, Julius. The Physiology of Plants, 227. 1887. il, Sehicesing, tl. Th. Vegetation comparee du Tabac sous cloche et i'air libre. Anns Gd. 801. Nat«, v¥.8er., 10 ; 366-869. 13869! 12. 14. 15. a3 Strasburger, E., Noll, ¥., Sehenck, H., and Schimper, A.?F.W. Ay Text-pook of Botany, 180, 189.1898 Tschaplowitz, F. Gibt es ein Transpirations—Optimm ? Bot. Zeit., got. 5 358-362. 1883. Wolliny, ". Unters. ueber den Finfluss d. Luftfeuchtigkeit auf Wachsthum. (Inaug. Diss.) Halle. See also Bot. C6ntralbl.s, 6: 249. 1898. Woods, A. Fe Researches on Transpiration and Assimilation. Bot. 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