22 TREES 



The bark protects the cambium, and the cambium is th« 

 tissue which by cell multiplication in the growing season 

 produces the yearly additions of wood and bark. Buds 

 are growing points set along the twigs. They produce 

 leafy shoots, as a rule. Some are specialized to produce 

 flowers and subsequently fruits. Leaves are extensions 

 of cambium spread in the sun and air in the season when 

 there is no danger from frosts. The leaves have been 

 called the stomachs of a tree. They receive crude ma- 

 terials from the soil and the air and transmute them into 

 starch under the action of sunlight. This elaborated sap 

 supplies the hungry cambium cells during the growing 

 season, and the excess of starch made in the leaf labora- 

 tories is stored away in empty wood cells and in every 

 available space from bud to root tip, from bark to pith. 



The tree's period of greatest activity is the early sum- 

 mer. It is the time of growi:h and of preparation for the 

 coming winter and for the spring that follows it. YV^inter 

 is the time of rest — of sleep, or hibernation. A bear digs 

 a hollow under the tree's roots and sleeps in it all winter, 

 waking in the spring. In many ways the tree imitates the 

 bear. Dangerous as are analogies between plants and 

 animals, it is literally true that the sleeping bear and the 

 dorr Aant tree have each ceased to feed. The sole activity 

 of each seems to be the quiet breathing. 



Do trees really breathe.^ As truly and as incessantly as 

 you do, but not as actively. Other processes are inter- 

 mittent, but breathing must go on, day and night, winter 

 and summer, as long as life lasts. Breathing is low in 

 winter. The tree is not growing. There is only the 

 necessity of keeping it alive. 



Leaves are the lungs of plants. In the growing season 



