in the nuts and they are poorly
filled or shriveled at harvest. Should the leaves of these trees in
midsummer or later be so seriously damaged by disease or insects as to
result in partial or complete defoliation, new growth is generally sure
to follow even in late fall if growing conditions are suitable. This
habit permits such trees to grow so late that there is much greater
danger of severe injury from late fall or early winter than is the case
with most other deciduous fruit trees. Furthermore, it explains why we
see so much cold injury in the shoots and limbs of trees; they had grown
late and had no chance to develop hardiness before killing temperatures
occurred.

After the rest in trees has become deep or profound a certain amount of
chilling temperature must prevail before the rest period is broken so as
to permit the buds to open and grow normally on the approach of warm
weather. This is often spoken of as the chilling requirement. If the
rest period is not broken by a suitable amount of chilling, tree growth
is very slow to start in the spring, and then only certain of the longer
and stronger twigs may force into growth; water sprouts may develop on
the trunks and main limbs; flower buds may not open but fall off; and
even though the trees may flower the flowering period is long and few or
no fruits or nuts may be set. The most effective chilling temperature is
not known but we can be reasonably certain that temperatures of 45 deg.F. to
32 deg.F. are just as effective in breaking the winter rest period as are
those well below freezing, if not more so.

This chilling requirement is essentially the same as the rest period.
Almonds have a short rest period and require 2 to 3 weeks of chilling,
while butternuts, with a long rest period, may require 3 or 4 months.
When the tree has been subjected to adequate chilling the rest period is
broken and with the oncoming of warm weather growth, blossoming and
fruit setting is normal.

A distinction of great importance from a physiological and a practical
point of view is made between rest and dormancy in plants. This
difference can be simply stated: plants, trees, or seeds that will not
grow when external environmental conditions are favorable for growth are
in rest, but after the rest period has been broken and they do not grow
because of unfavorable conditions they are said to be dormant.

The difference between rest period and dormancy is of great importance
in th