How Trees Spend the Winter 



The bark protects the cambium, and the cambium is the 

 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 specialised 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 materials 

 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 laboratories 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 summer. 

 It is the time of growth and of preparation for the coming winter 

 and for the spring that follows it. Winter 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 dormant 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 intermittent, 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 

 respiration goes on at a vigorous rate. The leaves also throw 

 off in insensible vapour a vast quantity of water. This is called 

 transpiration in plants; in animals the term used \s perspiration. 

 They are one and the same process. An average white-oak tree 

 throws off 1 50 gallons of water in a single summer day. With the 

 cutting off of the water supply at the roots in late fall, transpiration 

 is also cut off. 



The skin is the efficient "third lung" of animals. The 

 closing of its pores causes immediate suffocation. The bark 

 of trees carries on the work of respiration in the absence of the 

 leaves. Bark is porous, even where it is thickest. 



567. 



