THE FALL OF THE LEAF. 217 



begins to warp, and lets the now useless stele- 

 ton of the blade drop off with the wind. Those 

 large-leaved trees which thus learned to 

 economise their stock of food-stuffs were 

 alone able to compete advantageously with 

 the wiry and tough-skinned pines or firs ; and 

 thus many distinct families of forest trees, 

 such as the maples, the oak and beech tribe, 

 the elms, and the apple group, none of which 

 are at all related to one another, have quite 

 separately hit out the very same idea. Those 

 which did not hit it out went to the wall ; and 

 indeed our existing northern forest flora re- 

 presents, as it were, a mere fragment of the 

 original northern vegetation — the few scat- 

 tered species here and there among a vast 

 number which managed to adapt themselves 

 to the new and ungenlal conditions of the 

 northern zone. 



It is to this withdrawal of the green 

 colouring matter and the other living princi- 

 ples from the dying leaves that we owe the 

 tints of autumn, as Mr. Sorby has carefully 



