INFLUENCE OF SPECIFIC PECULIARITIES ON TRANSPIRATION 235 



probable that trees and even herbs would be unable to obtain the required 

 ash constituents in sufficient amount from the dilute solutions present in the 

 soil by the slow process of diffusion. Transpiration probably aids gaseous 

 exchange, and may also serve to prevent plants exposed to the sun from 

 being overheated. It is moreover, not impossible that transpiration and 

 the processes connected with it exert influences upon growth and develop- 

 ment which may be of the highest importance. How far this is true is 

 doubtful as yet, but, on these grounds .alone, it is possible that many plants 

 may be quite unable to live and develop when transpiration is prevented. 



No general conclusions can be drawn with regard to trees, &c., from the fact 

 that transpiration is unnecessary in submerged plants, whether amphibious or purely 

 aquatic, for the conditions under which they live are totally different Decisive 

 experiments upon these questions have not as yet been made, nor have trees been 

 grown under conditions where transpiration is impossible. Even in moist climates 

 this function suffices to very conspicuously aid in the transference of the constituents 

 of the ash to the leaves, &c.' Schlosing 2 found that tobacco plants grown under 

 bell-jars, so that but little transpiration was possible, did not grow as well as others 

 in the open. Though a variety of other factors enter into play here, such experi- 

 ments suffice to show that transpiration favours the absorption of the constituents 

 of the ash 3 . It is not yet known whether the plant accumulates more than it needs 

 when transpiration is active, and whether the necessary minimum can be absorbed 

 without the aid of transpiration. When the solution of any salt present in the soil 

 is comparatively concentrated, transpiration may actually cause it to accumulate to 

 an injurious extent (Sect. 23). 



Since transpiration and the processes connected with it indirectly favour 

 growth and development, there must be a certain optimal rate for each 

 plant, which will vary somewhat according to the moistness of the soil 

 and other external conditions. An excessive evolution of water-vapour 

 causes a diminution of turgidity, and hence a lessened rapidity of growth. 

 This conclusion is supported by comparative observations made upon 

 plants grown in atmospheres of varying humidity, and in soils containing 

 different percentages of water 4 . 



1 Haberlandt, Sitznngsb. d. Wien. Akad., 1892, Bd. ci, Abth. i, p. 809. Cf. also Stahl, I.e. ; 

 Burgerstein, Ber. d. Bot. Ges., 1897, p. 155; Giltay, Jahrb. f. wiss. Bot., 1897, Bd. XXX, p. 615; 

 Wiesner, Ann. d. Jard. bot. d. Buitenzorg, 1897, T. XIV, p. 277 ; [Haberlandt, Jahrb. f. wiss. Bot., 

 xxxi, 1897, p. 273; Giltay, I.e., 1898, xxxn, p. 453]. 



a Schlosing, Ann. d. sci. nat., 1869, v. ser., T. X, p. 366. Cf. also Kohl, Transpiration, 1886, 

 p. 113, and Ebermayer, Bot. Jahresb., 1884, p. 8. 



3 [Wollny (Unters. iiber den Einfluss d. Luftfeuchtigkeit auf Wachsthnm (Inaug. Diss.), Halle, 

 1898 ; cf. Bot. Centralbl., Bd. LXXVI, p. 249) finds that in moist air the dry weight and total amount 

 of salts become greater than in dry air. These results are probably due to the necessary protection 

 against transpiration in dry air retarding the gaseous exchange, and thus also carbon dioxide 

 assimilation and growth.] 



4 Tschaplowitz, Bot. Zeitung, 1883, p, 353 ; Gain, Ann. d. sci. nat., 1894, v. ser.,T. xx, p. 135 ; 

 Fittbogen, Versuchsst., 1870, Bd. xni, p. 109; Avedissian, Bot. Centralbl., 1896, Bd. LXVIII, p. 379. 



