THE PROCESSES OF ABSORPTION AND EXCRETION 101 



plant membranes saturated with pure water do not seem to allow any of the fats or 

 fatty acids with which they may be brought in contact to pass through them. The 

 emulsification theory is supported by the fact that the fatty acids, as well as the 

 neutral fats containing fatty acids, are readily emulsified by means of sodium 

 phosphate and other reagents, and this would explain the importance of the 

 presence of fatty acids for the translocation of solid fats or liquid oil 1 . It is 

 possible that the supposed solubility of fats in egg albumen, and in concentrated 

 sugar solution 2 , may be merely due to the production of a very fine emulsion. 



Wax, Balsams, and Ethereal oils are apparently not formed merely by changes 

 taking place external to the living cell, but probably are frequently, or even usually 

 produced by the protoplast, and subsequently pass through its substance, and through 

 the cell-wall to reach the regions where they are deposited 3 , or as in the case of 

 the essential oils which give flowers their perfume, they pass to the surface, and are 

 then slowly given off to the surrounding air. On the other hand, as the cuticle 

 develops and becomes impregnated with wax, the imbibed water with which it was 

 originally saturated is gradually expelled. 



SECTION 17. Special Account of the Processes of Absorption 



and Excretion. 



The general laws of diosmosis are directly applicable in determining 

 the exchanges which take place between the organism and the external 

 world. Every substance which can diosmose through the different cellular 

 membranes penetrates the protoplast, independently of whether it may be 

 useful, unnecessary, or even poisonous 4 . All observed facts are in harmony 

 with this law, although it is not always easy actually to determine the 

 conditions under which a particular result is obtained. Thus, not only is 

 the quality of the diosmosing substance of importance, but the fact that the 

 diosmotic properties of the plasmatic membrane may vary must be taken 

 into consideration, and moreover a substance may be changed and rendered 

 fit for diosmosis by intracellular or extracellular processes of more or less 

 uncertain character 5 . It must also be remembered that the plasmatic 

 membrane is a living and dependent organ, by means of which the protoplast 



1 Hermann, Handbuch d. Physio!., Bd. V, pp. 178, 291 ; Bunge, Lehrb. d. physiol. Chemie, 

 1894, 3. Aufl., p. 176 ; Quincke, Pfliiger's Archiv f. Physiol., 1879, p. 136. 



" Pacht, Centralbl. f. Physiol., 1888, Bd. II, p. 688. 



3 Pfeffer, I.e., p. 179, and the lit. there cited. 



* This is demonstrated by the marked amount of unnecessary ash constituents which may be 

 taken in, as well as directly by the absorption of aniline dyes. The older researches by Saussure 

 (Rech. chim. s. 1. Vegetation, 1804, p. 247), Vogel (Jour. f. prak. Chemie, 1842, Bd. XXV, p. 209), 

 Trinchinetti (Bot. Zeitung, 1845, p. in) see the literature given by Deherain, Ann. d. sci. nat., 

 1867, v. ser., T. vui, p. 1 80) are for us of little importance, for only the absorption by the entire 

 plant was determined, and in part the methods employed caused many of the protoplasts to die. 



5 See Pfeffer, Zur Kenntniss d. Plasmahaut u. Vacuolen, 1890, p. 279, and Unters. a. d. Bot. 

 Inst. z. Tubingen, 1886, Bd. II, p. 299. 



