96 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



Zea Mais, as well as of a polysaccharide, probably cane-sugar, which is 

 also one of the sugars excreted by nectaries. 



These illustrations may suffice to indicate that protoplasts can directly 

 absorb and excrete a variety of substances of both simple and complex 

 molecular constitution. There is, therefore, no occasion to doubt that the 

 numerous nutritive or waste substances, absorbed or excreted by the proto- 

 plast, diosmose directly without undergoing any preparatory change, unless 

 there are definite reasons to the contrary. Even fats and fatty acids may 

 be directly absorbed by living cells, and probably wander from cell to cell 

 in the form of a fine emulsion. 



Certain substances penetrate every living protoplast that has been 

 examined, but it is quite certain that more detailed and minute experimenta- 

 tion will show that qualitative and quantitative differences exist between 

 the respective diosmotic properties of such substances ; and, moreover, the 

 diosmotic properties of the protoplast may apparently become modified in 

 the progress of development in response to special external conditions. 



With regard to aniline dyes, acids, and alkalies, differences have 

 been recorded in the quantities absorbed by different cells. According to 

 Heidenheim l , however, the epithelial cells of the kidney can absorb and 

 excrete indigo-carmine, which is a pigment incapable of penetrating living 

 plant cells. By plasmolytic and other methods, differences in the power 

 and rapidity with which substances arc absorbed can be detected with 

 greater or less accuracy. 



Absorption of dyes, and the precipitations caused by these and other substances, 

 In the work previously quoted 2 , and in the studies connected therewith', a detailed 

 account of the absorption of aniline dyes will be found. In Sect. 22 these are 

 again mentioned, in so far as they demonstrate the selective powers of the living 

 cell and its powers of passive secretion. If plants of Lemna minor are allowed 

 to float on a 0-0005 P er cent, solution of methyl-blue, the blue colouration soon 

 observed in the roots is a visible indication that colouring material is absorbed 

 by them, and accumulated in the cell-sap. If we employ a leafy shoot of Elodea 

 the absorption of the dye is demonstrated by the marked colouration assumed 

 by the leaves, and by the gradual decolourization of the coloured solution in which 

 the leaves are immersed. Provided that the coloured solutions employed are 

 sufficiently dilute, normal growth continues, and a poisonous influence is only 

 exerted when the colouring material can penetrate the plasma to a sufficient 

 extent. Hence a large amount of the dye may accumulate in the cell-sap without 



1 Hermann, Handb. d. Physiologic, 1883, Bd. v, Abtheilung i, p. 346. Cf. Pfeffer, Unters. a. d. 

 Bot. Inst. z. Tubingen, 1886, Bd. II, p. 270. 



9 Pfeffer, 1. c. ; also Plasmahaut u. Vacuolen, 1890, p. 385. 



s \Vieler, Jahrb. f. wiss. Bot., 1888, Bd. XIX, p. 119; Wortmann und Stilling, Anilinfarbstoffe 

 als Antiseptica, 1890, p. 47 ; Overton, Bot. Centralbl., 1890, Bd. xi.iv, p. 6 ; and the works already 

 cited on p. 94, note i. In animals see Kowalevsky, Biol. Centralbl., 1889, Bd. IX, p. 33; Feist, 

 Physiol. Centralbl , 1890, Bd. iv, p. 324, &c. 



