THE FUNCTIONS OF THE WOOD 215 



except during the summer. This rule is broken by Ilex,* 

 where the concentration in the root is the greater through- 

 out the year, except in winter. The electrolytes, however, 

 are present as a rule in greater quantity in the root. 



11. In general the vessels function, in times when water 

 is abundant, to convey rapidly solutions of organic and 

 inorganic substances to the leaves. The columns of 

 tracheids may be supposed to afford a permanent channel 

 for the water and salts, and to a less degree for the organic 

 substances. This is never put out of action, even in times 

 of greatest drought. 



* The Ilex stem was examined at 1 metre above ground-level ; the 

 other stems were cut across much higher up. 



