when the stomata of the roots are interfered with. Such interference
may occur in cases where a heavy layer of soil is piled around the
base of a tree, where the soil about the base of a tree is allowed
to become compact, where a tree is planted too deep, or where the
roots are submerged under water for any length of time. In any case
the air cannot get to the roots and the tree suffers. Nature takes
special cognizance of this important requirement in the case of
cypress trees, which habitually grow under water. Here the trees are
provided with special woody protuberances known as "cypress knees,"
which emerge above water and take the necessary air. See Fig. 18.

Conclusions: From the foregoing it will be seen that trees have certain
needs that nature or man must supply. These requirements differ
with the different species, and in all work of planting and care as
well as in the natural distribution of trees it is both interesting
and necessary to observe these individual wants, to select species
in accordance with local conditions and to care for trees in
conformity with their natural needs.




CHAPTER V

WHAT TREES TO PLANT AND HOW


The following classification will show the value of the more important
trees for different kinds of planting. The species are arranged in the
order of their merit for the particular object under consideration and