THE VEGETABLE KINGDOM. 373 



the one hand, a root be plunged uninjured into a saline so- 

 lution, and, on the other, a similar plant be immersed, after 

 having its members cut short off, it will be seen at the end 

 of a certain time that the uninjured plant has not absorbed 

 the salt in the same proportion as it is found in the solution, 

 whereas that which has had its roots divided has been aban- 



176. Ice -Plant: Mesembryanthemum crystallinum (Linnaeus). 



doned to the dominion of physico-chemical causes, and has 

 pumped up the liquid without making any selection. 1 



Water is the principal food of the plant, but the radicles 

 also take up other substances from the earth. They re- 

 quire carbon and nitrogen. The grasses demand a certain 



1 The sea, which contains thirty times as much sodium as potassium, furnishes 

 to some of the Algae, drawing all their mineral matter from it, equal quantities of 

 these two metals, and to many others half as much potassium as sodium. TB. 



