1 18 THE MECHANISM OF ABSORPTION AND TRANSLOCA TION 



certain substances, and it is possible that their permeability may be markedly 

 affected by a formation of precipitation membranes, when salts of calcium 

 or iron come into contact with them, and form definite compounds. It is 

 in virtue of some such action, that when a bladder containing a solution of 

 ferric chloride is immersed in hard tap-water, none of the iron salt diffuses 

 through the membrane. 



The possession of a power of swelling, or of allowing transpiration to pro- 

 ceed, shows that no cork or cuticle is absolutely impermeable to water. Thus 

 when KNO, or K 2 SO 4 is placed upon a moistened and wetted area of the thin 

 cork layer covering potatoes, or of the thick cuticle covering the leaves of Hex, 

 Primus Laurocerasus, &c., a little water is very slowly absorbed by the salt from 

 the leaf or potato '. Since the energy exerted by a saturated solution of KNO S in 

 drawing water through a cuticular or corky membrane corresponds to a pressure 

 of about seventy atmospheres, it is easy to understand why various authors have 

 been unable to obtain any perceptible filtration of water through thin lamellae of 

 cork by the aid of an air-pump *. 



The osmotic passage of salts may be indicated by the production of plasmolysis 

 and by observing the rapidity with which the salts pass, while from the amount of 

 plasmolysis produced in a given time, it may be shown that the cuticle of exposed 

 aerial parts is far less readily permeable than that of submerged parts. Experiments 

 with separated multicellular hairs show that the salt penetrates with much greater 

 rapidity through the uncuticularized transverse walls. The same thing is indicated 

 when the change of colouration is followed, which dilute ammonia produces in the 

 coloured cell-sap of the staminal hairs of Tradescantia, or in that of the leaf 

 tentacles of Drosera s . It is not necessary to mention in detail different researches, 

 in which by other methods the passage of certain salts through the cuticle of leaves, 

 &c. has been demonstrated 4 . The absorption of water, which causes certain pollen 

 grains to hurst, will be referred to later (Sect. 22)", and no detailed description 

 will be given here of the formation, distribution, or special peculiarities of the cork, 

 cuticle, or cuticular layers of different plants *. 



Biisgen (Honigthau, 1891, p. 36), in the objections raised by him, has apparently failed to 

 realize the meaning of the wetting, or the enormous energy which osmotic forces can exert. See 

 Pfeffer, Studien z. Energetik, 1892, p. 266. On wetting, Lehmann, Mol.-physik, 1889, Bd. II, 

 p. 1 06, 8cc. 



2 Hofmeister, Pflanzenzelle, 1867, p. 238; Eder, Sitzungsb. d. Wien. Akad., 1873, Bd. LXXH, 

 Abth. i, p. 258; Zacharias, Bot. Zeitung, 1879, P- 6 44- 



Pfeffer, Osmot. Unters., 1877, p. 199. In connexion with the* absorption of aniline dyes, see 

 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 201. 



Boussingault, Agron., Chim. agr. et Physiol., 1878, Vol. VI, p. 364; Wille, Cohn's Beitrage, 

 1887, Bd. xiv, p. 314; Burgerstein, Ubersicht iiber d. Unters. u. d. Wasseraufnahme d. Blatter, 1891 

 (Sep.-abdr. a. d. Jahresb. d. Leopoldstadter Gymn. in Wien). 



* On the protective sheaths of vascular tissues, &c., see Schwendener, Die Schutz-Scheiden u. 

 ihre Verstarkungen, 1882, p. 6. 



6 See de Bary, Vergleichende Anat., 1877, pp. 77, 114; Zimmermann, Pflanzenzelle, 1887, 

 p. 117; Mikrotechnik, 1892, p. 146; Tschirch, Pflanzenanatomie, 1889, p. 117; E. Weiss, Beitrage 

 z, Kennt. d. Korkbildung, 1890 (Denkschr. d. Regensburger Bot. Ges.). On the duration of the 



