THE LIFE OF THE TREES 17 



learned by experience in contact with cold winters. The 

 swamp magnoha is a beautiful evergreen tree in Florida. 

 In Virginia the leaves shrivel, but they cling throughout 

 the season. In New Jersey and north as far as Glouces- 

 ter, where the tree occurs sparingly, it is frankly deciduous. 

 Certain oaks in the Northern states have a stubborn way of 

 clinging to their dead leaves all winter. Farther south 

 some of these species grow and their leaves do not die in 

 fall, but are practically evergreen, lasting till next year's 

 shoots push them off. The same gradual change in habit 

 is seen as a species is followed up a mountain side. 



The horse-chestnut will serve as a type of deciduous 

 trees. Its leaves are large, and they write out, as if in 

 capital letters, the story of the fall of the leaf. It is a 

 serial, whose chapters run from July until November. The 

 tree anticipates the coming of winter. Its buds are well 

 formed by midsummer. Even then signs of preparation 

 for the leaf fall appear. A line around the base of the leaf 

 stem indicates where the break wdll be. Corky cells form 

 on each side of this joint, replacing tissues which in the 

 growing season can be parted only by breaking or tearing 

 them forcibly. A clean-cut zone of separation weakens the 

 hold of the leaf upon its twig, and w^hen the moment arrives 

 the lightest breath of wind — even the weight of the with- 

 ered leaf itself — causes the natural separation. And the 

 leaflets simultaneously fall away from their common pet- 

 iole. 



There rre more important things happening in leaves in 

 late summer than the formation of corky cells. The plump 

 green blades are full of valuable substance that the tree can 

 ill afford to spare. In fact, a leaf is a layer of the precious 

 cambium spread out on a framework of veins and covered 



