t. The fruit had all been harvested from
certain of these trees for two weeks or more before the occurrence of a
freeze the last of November. From other trees the fruit crop had only
been partially harvested and none had been harvested from most of them.
The day and night temperatures had been warm but there was a rather
sudden drop into the low 20's during one night with the result that all
of the trees from which no fruit had been harvested were killed to the
ground. The trees from which a part of the fruit had been removed were
defoliated and all but the large limbs were killed. The trees from which
all the fruit had been removed two weeks or more before the freeze were
defoliated, but little or no injury to the woods occurred. The severe
injury was probably because the materials making for hardiness in the
wood had been transported to the maturing fruits and the temperature
dropped quickly before the trees had time to develop cold resistance.

It is a well-known fact that many kinds of non-woody as well as many
woody plants develop hardiness or cold resistance on exposure to very
gradually falling temperatures. This change, in the case of non-woody
plants such as cabbage or wheat, is spoken of as "hardening off." It is
not known how important this is in developing cold resistance in flower
and leaf buds of woody plants. It is quite possible that buds that have
become extremely tender as a result of rapid growth might, if held for
some time at temperatures too low for further growth, become quite
resistant to low temperatures just as do wheat or cabbage.

Generally speaking, the greatest amount of cold injury to the buds or
above-ground portions of a tree occurs on a single night. The length of
the cold period is of only indirect importance as influencing the rate
of temperature fall or the acquiring of cold resistance by the trees.
Trees that are subjected to low temperatures over a considerable period
of time are not nearly so likely to be injured as are those that are
subjected to a low temperature suddenly. That is really why there is so
much severe cold injury to woody plants in the South. In the deep South
freezing weather may be uncommon but when freezes do occur usually they
follow a period of comparatively warm weather and the temperature falls
quickly. It is this sudden change in temperature that causes the severe
injury. Two different places may have had the same mean monthly
temperature yet at one place s