160 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



(Sect. 65) in which leaves or parts of leaves may be specially modified 

 to form absorptive organs 1 . 



The leaves of land-plants are never completely incapable of absorbing 

 water, provided that they can be wetted (Sect. 21), and hence in any given 

 case it is simply a question as to the extent to which this power has 

 been developed and increased, or how far it is employed under the given 

 conditions. In typical land-plants, the leaves have no practical importance 

 as absorptive organs for fluids, owing to their relative impermeability 

 and to the causes previously mentioned. A little of the water collected 

 in the leaf-sheaths of Dipsacns, Umbelliferae, &c., may be absorbed, 

 although these plants do not normally require any supply of water from 



this source. It must moreover always 

 be remembered that the properties of 

 the cuticle, including its permeability 

 to water, may be markedly modified by 

 the cultural conditions (Sect. 21). 



The gradual recovery of a flaccid leaf, 

 when the lamina is immersed in water, 

 shows directly that water has been ab- 

 sorbed through the outer surface. If, 

 as in Fig. 15, half of a leafy branch is 

 immersed in water, the withering of the 

 leaves exposed to air may be prevented, 

 as was first observed by Marriotte and 

 Hales *. In other plants, the absorption 

 of water only suffices to slightly delay the 

 withering of the exposed portion (Wiesner). 

 By weighing this apparatus (Fig. 15), the 

 amount of water transpired, and hence the 



approximate amount absorbed, may be found. Boussingault s has shown that 

 the latter is not always trifling, and that the surfaces of the branches allow but 

 little water to penetrate, while water may be absorbed by leaves which possess 

 few or no stomata. These results have been confirmed by other observers, and 

 according to Wiesner's researches, even the leaves of Sedum Fabaria can absorb 

 a little water 4 . 



1 On the absorption of water by the trumpets of Sarracenia, cf. Wiesner, quoted by Btirgerstein, 

 Wasseraufnahme d. Pflanzen, 1891, p. 28. On the pitchers of Dischidia rafflesiana, see Treub, 

 Ann. d. Jard. bot. d. Buitenzorg, 1882, T. n, p. 32; [Groom, Ann. of Bot., 1893, vol. vii, p. 223 ; 

 Scott and Sargent, ibid., p. 243]. 



2 Mariotte, CEuvres d. Mariotte, 1717, p. 133; Hales, Statics, 1748, p. 78. 

 1 Boussmgault, Agron., Chim. agiic., &c., 1878, T. VI, p. 364. 



4 A complete bibliography is given by Biirgerstein, t'bersicht der Unters. iiber die Wasser- 

 aufnahme der Pflanzen durch die Oberflache d. Blatter, 1891 (Sep.-abdr. a. d. 27. Jahresb. d. Leopold- 

 stadter Obergymnasmms in Wien). Of the special works may be mentioned : Wiesner, Sitzungsb. 

 d. \\iener Akad., 7882, Bd. LXXXVI, p. 241 ; Kny ; Ber. d. Bot. Ges., 1886, p. xxxvi ; Wille, Cohn's 



