the
(5) partial, then complete, destruction of the tree.

On the other hand, the fact that a tree is subject to occasional winter
injury, or that it bears irregularly, or not at all in a particular
site, is not necessarily to be taken that the same tree in a different
site or under slightly changed environment would not perform
satisfactorily, even in the same locality. A change in exposure or of
cultural treatment, or of rootstock, or of variety, or a modified
association of varieties, might and frequently does bring about entirely
different results. Sometimes a southern exposure causes trees to respond
to mild weather, in winter or early spring, and to be caught by
subsequent, violent drops in temperature. Some of the best known and
best performing Persian walnut trees in the East are on a northwestern
exposure, yet the species is commonly not hardy in the temperate
portions of this country.

To a certain extent the ability of orchard trees to withstand frost
injury is subject to control. The danger is greatest with trees which
have grown late or those which have become devitalized for some reason
or with those which are in poorly drained soils. The kind of root stock
which has been used, is known to have had an influence in some cases.
Doubtless this will be better understood as different stocks are used by
the leaders in pecan breeding. Varieties also are known to differ
greatly in their degree of hardiness. However, failure upon the part of
otherwise normal trees to bear paying crops with regularity is not
necessarily due to low temperatures. Other factors, such as
self-sterility, may be wholly responsible for at least the lightness of
crops.

So far as the orchardist is concerned, a tree is not hardy unless it is
capable of bearing crops the average of which are profitable. On the
other hand, occasional winter injury does not prove that a species
cannot be grown successfully in the same locality. Neither the peach nor
the apple industries of the North nor those of the citrus in the South
and California nor, in fact, any of the other horticultural commodities
of this country are wholly unaffected by frost damage. Our forest trees
may be more subject to winter killing than we suspect. A certain amount
of winter-injury is to be expected in any part of the country no matter
what the species of plant may be.

The frequency with which winter or spring injury is definitely known to
occur gives color to a rising