trees these openings are very
    conspicuous and are there known as lenticels.  These pores are
    necessary for the breathing of the tree (respiration), whereby
    carbonic acid gas is taken in from the air and oxygen given out.  The
    process of assimilation depends upon this breathing process and it
    is therefore evident that when the stomata are clogged as may occur
    where a tree is subjected to smoke or dust, the life processes of
    the tree will be interfered with.  The same injurious effect results
    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 the comments accompanying each tree are intended to bring out its special qualifications for that purpose.

Conditions for tree growth in one part of the country differ from those of another and these lists, especially applicable to the Eastern States, may not at all fit some other locality.

TREES BEST FOR THE LAWN

DECIDUOUS

1.  American elm (Ulmus americana)

    One of the noblest of trees.  Possesses a majestic, wide-spreading,
    umbrella-shaped crown; is easily transplanted, and is suited to a
    variety of soils.

2.  Pin oak (Quercus palustris)

    Has a symmetrical crown with low-drooping branches; requires a moist
    situation.

3.  European linden (Tilia microphylla)