fferent
elevations. The planting at the lowest elevation, maintained as a well
cultivated orchard, suffered almost 100 per cent loss from this fall
freeze. The trees at the highest elevation, in a forest planting, were
practically uninjured. The damage from this freeze varied from killing
of buds and shoots to killing of complete trees. Many owners of chestnut
plantings did not notice the damage until the following spring.
Fortunately fall freezes of this magnitude occur only infrequently.

In the winter of 1944, this Division lost 23 per cent of its hybrids at
Glenn Dale, Md., from freezing following abnormally high temperatures.
The hybrids had been fertilized in October of the preceding year, but
the effect on the extent of freezing damage is not known. The months of
November, 1943, through March, 1944, were characterized by extremely
variable temperatures. For example, in November a minimum of 15 deg. F.
occurred on the 17th, a maximum of 72 deg. on the 19th; in December a
maximum of 66 deg. on the 3rd, a minimum of 2 deg. on the 16th; in January a
minimum of 8 deg. on the 17th, a maximum of 74 deg. on the 27th; in February a
minimum of 11 deg. on the 2nd, a maximum of 72 deg. on the 25th; in March a
minimum of 8 deg. on the 10th, a maximum of 81 deg. on the 16th.

The extremes of temperatures in any one of these months may have been
sufficient to cause damage to chestnut, although the extent of damage is
influenced by the physiological conditions within the tree. The usual
type of injury to the hybrids was a killing of the cambial cells
extending from the base of the trunk up to varying heights. The cambial
region was grayish-black and the inner bark was sappy and
greenish-brown. More trees were injured and killed on the lower portions
of the plot than on the higher portions.

This catastrophe afforded opportunity to study resistance of the hybrids
to freezing. In the lower part of the plot there were several 3-year-old
American chestnut seedlings that were not damaged. Sixteen per cent of
first generation hybrids of Chinese and American chestnut were killed.
Chinese by American backcrossed with Chinese were killed to the extent
of 36 per cent. Chinese by Japanese chestnut of the second generation
were killed to the extent of 35 per cent.

Despite this extensive killing of hybrids by extreme variations of
winter temperatures, older Chinese and Japanese chestnuts on slightly
higher ground in the same plot suffere