238 BOTANICAL MICROTECHNIQUE. 



indicators into the living cell. In fact, Pfeffer has (II, 259 

 and 266) already shown the alkaline reaction of the cytoplasm 

 in various cells by the aid of cyanin and methyl orange. 



17. Plasmolysis (Plasma-membranes). 



428. If living plant-cells are placed in a solution of salt or 

 the like, the protoplasm withdraws from the wall in the form 

 of a continuous sac, if the solution be above a certain 

 degree of concentration, in consequence of its power of 

 taking up water. This proceeding, now generally known as- 

 plasmolysis, offers the best means of showing the continuity 

 of the protoplasmic body in cells poor in protoplasm, and it 

 also plays an important part in various morphological and 

 physiological researches. 



429. Concerning the media used in plasmolysis, it is 

 especially important that they shall exert no unfavorable 

 influence on the cells in the degree of concentration in which 

 they are employed. They should also have neither a 

 markedly acid nor an alkaline reaction. It is best, then, to 

 use neutral salts like saltpeter (KNO 3 ) or salt (NaCl), or 

 organic compounds like cane-sugar or glycerine. The latter 

 has the advantage, in some cases, of exerting a clearing 

 effect in consequence of its higher refractive index. No 

 general directions can be given as to the concentration of 

 the solutions to be used, and in the choice of the proper 

 concentration the isotonic coefficient * of the compound used 

 should be especially regarded. But, in general, clearly visi- 

 ble plasmolysis may be obtained by using a 4$ solution of 

 saltpeter or a 15$ solution of cane-sugar. 



430. If the objects to be plasmolyzed are not prescribed 

 by the nature of the investigation, it is best to choose such 

 objects as are most adapted to the observation of plasmoly- 

 sis, and as. have the greatest power of resisting the injurious 

 influences connected with their preparation. Thus the cells 

 of Spirogyra furnish very suitable material for the demon- 

 stration of plasmolysis. Such cells as naturally contain a 



* [Cf. Zimmermann I, 199-201 : also below, p. 263.] 



