20 Characteristics, Structure, Life of Trees 
growth of buds and foliage. Hence a deficiency in food 
elaboration or defoliation in one year may, according to the 
time when it occurs, influence the growth and health of that 
and the next year; or the unfavorable season of one year 
may not show its effects until the following season. 
Besides food, a tree, like an animal, needs air or oxygen 
for respiration. The importance of this fact is perhaps 
very imperfectly realized by the uninitiated. Yet not only 
the leaves but also the twigs, branches and bole, and even 
the roots have breathing pores in the developed fissures 
of the bark, for the purpose of conducting air into the 
interior. 
That the roots must breathe is often forgotten, as when 
trees are planted too deep, or when ground is filled in on 
top of them Many a tree is lost by this ignorance. The 
more compact the soil and the deeper the cover, the surer 
and quicker the result, the tree dying from suffocation. ‘The 
same result is induced by flooding, or even a very rainy sea- 
son may, on compact soil, so reduce the aeration of the roots 
as to kill them. Trees growing in swamps have adapted 
themselves gradually to the difficulty of root respiration, 
and the ground around trees grown in such conditions may 
be filled up without the same detriment that would come to 
trees not so adapted. 
Whenever there is a change made in the surroundings, 
especially in soil and in light conditions, there must take 
place an adaptation of the root system to the change. The 
tree, however, can make this adaptation only gradually, 
hence any contemplated change in the environment must be 
made by degrees or else the tree will suffer. 
It appears from the brief description of the household 
economy of the tree, that the requisites for tree life are, 
like that of other plants, first of all, at the root: — 
