THE LEAVES. 141 



of water to this crevice, and its freezing, serve to rupture the 

 remaining tissues, and thus allow the leaf to fall by its own 

 weight, or to be torn off by the wind. 



The scar left by the fall of the leaf is protected either by 

 the cork already produced, or by mere drying of the exposed 

 tissues. The leaflets of compound leaves fall in like manner. 

 Sometimes provision for the leaf fall is begun as early as June, 

 as in the Kentucky coffee-tree. In other plants provision 

 for leaf-fall is begun late in the season, and in some, such as 

 the oaks, it is very imperfect, so that the leaves are finally 

 wrenched off by winter storms, or pushed off in the spring by 

 the developing buds beneath them. 



