i;8 ELEMENTARY BIOLOGY 



from the leaves to the roots, since by far the largest portion 

 of it is transpired and never comes back. 



The ascending current is for the most part inorganic in its 

 composition ; the descending current is in large part organic. 



The two currents are nowhere continuous. They are prac- 

 tically independent of each other, except, of course, that the 

 life of the plant can continue normally only when both cur- 

 rents are maintained ; yet one may go on for a considerable 

 time without the other being in action. 



