THE Dl OSMOTIC PROPERTIES OF THE CELL 97 



producing any injurious effect, provided that it is in the form of a non-diosmosing 

 compound. 



The different forms in which the dye accumulates, as well as the varying 

 results which the same pigments produce on different plants, indicate that the 

 substances which render accumulation possible are not always identical. Of 

 those substances, which cause a deposition of pigment in the cell-sap, the best 

 known are Tannin and Phloroglucin. Other substances may also be active, but 

 their nature is as yet obscure. In some cases two or more such substances may 

 be present in the cell (Pfeffer, I.e., pp. 191, 273), and by their combined action 

 determine whether the absorbed dye shall accumulate in the cell in soluble, or 

 insoluble, form \ When a pigment is precipitated inside the cell, it may also remove 

 other substances present in the cell-sap, either mechanically or in combined form. 

 Treatment with caffein, antipyrin or ammonium carbonate causes any tannin 

 present in the cell-sap to be precipitated, and the presence in the cell of other 

 substances, of which phloroglucin is the only one known 2 , may cause similar pre- 

 cipitation when tissues are treated with the above re-agents. Since these substances, 

 which may be said to be the agents of passive secretion, vary both as regards the 

 nature and the number of them present in the cell, it is clear, that the above 

 reaction may, or may not, form a direct test of the extent to which the cell in 

 question can passively secrete aniline dyes. It is easy also to understand,, that it 

 may be possible for one plant to absorb Methyl-blue and also Bismarck-brown, while 

 another only absorbs the former 3 . 



The precipitates formed when certain cells are treated with caffein are un- 

 doubtedly insoluble compounds produced by the union of the reagent with 

 substances present in the cell. Whether the precipitation caused by ammonium 

 carbonate is of similar nature is doubtful, for precipitates may also be formed by 

 neutralization or crystallization. On treatment with water, the precipitates pro- 

 duced by ammonium carbonate, caffein, &c. re-dissolve, but this merely indicates 

 that the reagents in question may be readily removed by water from the living cell. 

 A similar diosmotic separation of the absorbed substance from that with which it 

 combines may take place either normally, or only under special conditions, when 

 the living cells absorb aniline dyes (Sect. 22). As a general rule, these reactions take 

 place only in the cell-sap, but it need not surprise us if we find them occurring in the 

 plasma in certain cases 4 , indeed, as a matter of fact, certain aniline dyes do actually 

 accumulate in the plasma. Even when in certain cases the precipitate is perhaps 

 found to consist of a double phosphate of ammonium and magnesium, or of proteid 

 compounds, the essential features of the phenomenon will still remain the same. 



1 See Pfeffer, I.e., pp. 232, 245; Lehmann, Zeitschr. f. physik. Chemie, 1894, Bd. xiv, p. 157. 



2 Loew u. Bokorny, Bot. Zeitung, 1887, p. 849; Flora, Erganzungsband, 1892, p. 117, &c. ; 

 Klemm, Ber. d. Bot. Ges., 1892, p. 237 ; Flora, 1892, p. 400 ; Bot. Centralbl., 1894, Bd. LVII, p. i<>~ ; 

 Zimmermann, Beihefte z. Bot. Centralbl., 1893, Bd. in, p. 324; further literature here quoted. 

 On the precipitates which Darwin found Am. carbonate might produce, see Klercker, Studien u. 

 Gerbstofivacuolen, 1888 (Tiibinger Dissertation: ; Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, 

 Bd. II, p. 239, and Flora, 1889, p. 52. 



3 Klemm, Flora, 1892, p. 412 ; Pfeffer, Unters. a. d. Bot. Inst. z. Tiibingen, I.e., pp. 191, 273. 



4 See Klemm, Flora, 1892, p. 408 ; Zimmermann, 1. c. 



HFF.FFER I I 



