Martin : Effect of concentrated solutions 423 



Variation in different plants, — It seems quite evident that 

 plants may adapt themselves to environment in which it is diffi- 

 cult to obtain or to retain water, by increased concentration of the 

 cell-sap. Pantanelli (19) quotes Cavaras to the effect that cold- 

 enduring, salt and rock plants possess a very concentrated cell- 

 sap. Ganong (8) remarks that there seems to be a close corre- 

 spondence between halophilism of the plant and the power of its 

 root-hairs to resist plasmolysis. The above experiments show 

 that cells of the red beet have a much more concentrated cell- 



« 



sap than Tradescantia, 



Variation in different parts of plants, — De Vries (29) notes 

 that the concentration necessary for plasmolysis differs for differ- 

 ent parts or tissues of a plant, as well as for different plants. 

 Apical cells have been generally considered to be much more 

 difficult to plasmolyze than other cells, and the limit of concen- 

 tration necessary to produce plasmolysis to decrease as the age of 

 the cell increases {cf, Pfeffer 23, page 317 ; Ewart 6, page 12 ; de 

 Vries 29). The above experiments with Philotria showed these 

 variations clearly. The cells of the midrib were very difficult to 

 plasmolyze, while those in adjoining parenchyma were usually 

 among the first to show plasmolysis, as well as being plasmolyzed 

 more strongly. But there seems to be some relation between the 

 plasmolyzing substance in the substratum and the reaction of the 

 apical and older cells, which would result from the varying per- 

 meability of the protoplast for different substances. In solutions 

 of potassium nitrate and of urea, the cells near the midrib were 

 plasmolyzed to a greater degree than the apical cells. The 

 degree of plasmolysis, incipient in the apical cells gradually, 

 increased in the older cells. With glycerine, however, the 

 stronger plasmolysis occurred in the apical cells. But these cells, 

 after turgidity had been restored, were the last to be replasmo- 

 lyzed by potassium nitrate. Their greater permeability had 

 allowed more of the glycerine to penetrate the protoplast, so 

 that the concentration of the cell-sap was increased to a greater 

 extent. 



Permeability of plasma-membrane. — The permeability of the 

 plasma membrane has been shown for many substances. Hampe 

 (9), Beyer (2), de Vries (33), Klebs (10) and others have shown 



