It would seem that trees of the cone type possessed certain advantages
in some latitudes or elevations over other trees. (1) A conical tree,
like the spruces and larches and the pines, and hemlocks also, before
they get very old, meets with less injury during high winds than trees
of an oval or spreading type. The slender top of the tree where the
force of the wind is greatest presents a small area to the wind, while
the trunk and short slender branches yield without breaking. Perhaps
this is one reason why trees of this type exist in more northern
latitudes and at higher elevations in mountainous regions, and why
the spruce type reaches a higher latitude and altitude even than the
pines. (2) The form of the tree is such as to admit light to a large
foliage area, even where the trees are growing near each other. The
evergreen foliage, persistent for several years, on the wide-spreading
lower branches, probably affords some protection to the trees since
this cover would aid in maintaining a more equable temperature in the
forest cover than if the trees were bare during the winter. (3) There
is less danger of injury from the weight of snow since the greater
load of snow would lie on the lower branches. The form of the branches
also, especially in the spruces, permits them to bend downward without
injury, and if necessary unload the snow if the load becomes too heavy.
=717. The oval type.=—This type is illustrated by the oak,
chestnut, apple, etc. The trees are usually deciduous, i.e., cast
their leaves with the approach of winter. The main axis is sometimes
maintained, but more often disappears (trunk is _deliquescent_),
because of the large branches which maintain an ascending direction,
and thus lessen the importance of the central axis which is so marked
in the cone type. Trees of this type, and in fact all deciduous trees,
exhibit their character or habit to better advantage during the winter
season when they are bare. Trees of this type are not so well adapted
to conditions in the higher altitudes and latitudes as the cone type,
for the reason given in the discussion of that type. The deciduous
habit of the oaks, etc., enables them to withstand heavy winds far
better than if they retained their foliage through the winter, even
were the foliage of the needle kind and adapted to endure cold.
=718. The deliquescent type.=—The elm is a good illustration of
this type. The main axes and the branches fork by a false dichotomy, so
that a trunk is not developed except in the forest. The branches rise
at a narrow angle, and high above diverge in the form of an arch. The
chief foliage development is lofty and spreading.
Trees possess several advantages over vegetation less lofty. They may
start their growth later, but in the end they outgrow the other kinds,
shade the ground and drive out the sun-loving kinds.
II. Creeping, Climbing, and Floating Stems.
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