THE LIFE OF THE TREES 23 



respiration goes on at a vigorous rate. The leaves also 

 throw off in insensible vapor a vast quantity of water. 

 This is called transpiration in plants; in animals the term 

 used is perspiration. They are one and the same proc- 

 ess. An average white oak tree throws off 150 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. 



Look at the twigs of half a dozen kinds of trees, and find 

 the little raised dots on the smooth surface. They usually 

 vary in color from the bark. These are lenticels, or breath- 

 ing pores — not holes, likely to become clogged with dust, 

 but porous, corky tissue that filters the air as it comes in. 

 Li most trees the smooth epidermis of twigs is shed as the 

 bark thickens and breaks into furrows. This obscures, 

 though it does not obliterate, the air passages. Cherry 

 and birch trees retain the silky epidermal bark on limbs, 

 and in patches, at least, on the trunks of old trees. Here 

 the lenticels are seen as parallel, horizontal sHts, open some- 

 times, but usually filled with the characteristic corky sub- 

 stance. They admit air to the cambium. 



There is a popular fallacy that trees have no buds until 

 spring. Some trees have very small buds. But there is no 

 tree in our winter woods that will not freely show its buds 

 to any one who wishes to see them. A very important 

 part of the summer work of a tree is the forming of buds 

 for next spring. Even when the leaves are just imfolding 



