General Physiology of the Plant. 



201 



by thin films of water, and it is this water (hygroscopic 

 water) which is believed to be the medium for the trans- 

 ference of the salts from the soil to the cell. The water 

 thus absorbed is replaced by more water drawn by capillary 

 attraction from the more distant soil. It has been found 

 that a dilute solution of a salt is more easily absorbed than a 

 strong solution, and that the power of roots to absorb is 

 greater when the temperature is high than when it is low. 



FIG. 103. PLASMOLYSIS, illustrated on parenchyma from the peduncle 

 of Cephalarta leucantha. (De Vries.) 



A, turgid cell ; B, the same cell in 4 p.c. nitre solution ; c, in 6 p.c. so'u- 

 tion ; P, in 10 p.c. solution, showing complete plasmolysis ; A, cell- 

 wall ; /, protoplasm ; A; nucleus ; c, chlorophyll corpuscles ; s, cell- 

 sap ; e, nitre solution. 



This latter fact is to be explained by the increased evapora- 

 tion of water from the leaves under a high temperature. 



Different plants, as we have already seen, require different 

 salts in varying proportions. What, then, governs the ab- 

 sorption of a salt ? Apparently the need of it by the plant, 

 that is to say, a vital (for want of a more scientific term) and 

 not a physical necessity. The extent to which any plant 

 absorbs a particular salt is termed its specific absorbent 

 capacity for that salt. The salt absorbed is assimilated, 



