SPECIAL METHODS. 243 



pounds, as, for example, by a .1$ solution of coffein. These 

 may lie partly in the cytoplasm and partly in the cell-sap, 

 and, since they also occur in cells free from tannin, cannot 

 consist of tannin in all cases, at least, But to what extent 

 proteid substances or " active albumen " (cf. 445), which 

 forms their chief constituent, according to Bokorny, occur 

 in them cannot be certainly determined from our present 

 "knowledge. It is not impossible that we have here to do 

 with very various bodies. 



443. Precipitates occurring in plasmolysis were first 

 observed by Pfeffer (II, 245) in the root-hairs of Azolla, and 

 they occurred in the same manner whether the plasmolysis 

 was accomplished by means of sugar, saltpeter, or calcium 

 chloride. These precipitates agree essentially with those 

 produced by ammonium carbonate, and consist chiefly 

 of tannin, in most cases. But, as af Klercker (I, 29) has 

 .shown, other substances must be present in the cell-sap 

 which remain dissolved in the vacuolar fluid during the 

 excretion, and prevent the partial re-solution of the tannin. 

 It is also noteworthy that Klercker (1, 43) has observed similar 

 precipitates in artificial cells of tannate of glue, on plasmo- 

 lyzing them with a solution of saltpeter, while plasmolysis 

 with sugar contracted the whole cell into a glassy mass. 



444. Plasmolytic precipitates which are not due to the 

 presence of tannins may be very easily ob- 

 served in the epidermal cells of the red under 



surface of the leaves of Tradescantia discolor. 

 If tangential sections of these cells be placed in 

 a small dish with a io# solution of saltpeter, it 

 may be seen in ten minutes that strong plasmo- 

 lysis has taken place in all the cells, and pretty 

 strongly refractive, deeply colored spheres (cf. FlG . 62 .-E P ider- 



., s . 11 i M j.i 11 mal cells from 



Fig. 62) occur in most cells, while the cell-sap the under side of 



, ,, i the leaf of Tra- 



has in some cases become markedly clearer, descantia discolor 



. ., plasmolyzed with 



If water is afterwards added, these precipitates a % saltpeter 



. . . solution, show- 



are redissolved. No precipitates are produced ing piasmo 



, precipitates. 



in these cells by ammonium carbonate, and no 

 blackening occurs with osmic acid. 



