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 suffered no visible injury. These old trees have rough bark, which may serve as an effective insulator against extremes of temperature. In 1944, there was no damaging late spring frost, and these old trees produced the largest nut crop in their history. Winter temperatures of -25 deg. F. or lower are usually injurious to Oriental chestnuts. A few reports of chestnuts surviving temperatures of -25 deg. F. have been recorded, but usually Oriental chestnuts do not thrive in those northern States or regions where such temperatures occur. Many of our cooperators report that late spring frosts frequently cause failure of chestnut crops. Damaging frosts in late spring occur more frequently and over greater areas than early fall frosts or extreme winter temperature variations. A late spring frost in 1945 reduced the chestnut crop at Glenn Dale, Md., from 50 bushels expected to 3 bushels actual. A freeze of 24 deg.F. on the nights of April 4 and 5 was sufficient to inflict this damage after two weeks of abnormally warm weather. Many of the trees were visibly injured, with wilted or dried unfolding buds. Other trees on higher ground were not visibly affected, yet they produced no crops. Again it was noted that the American chestnut, followed by American chestnut hybrids, sustained none to little damage. The American chestnut, besides its inherent resistance to freezing, leafs late in the spring. Most of the crop of nuts obtained in 1945 was produced by the American chestnut hybrids. Late spring frosts in 1945 were very extensive, reaching throughout the eastern and northeastern States, and there were practically no chestnut crops. There were also numerous reports of late spring frost injury to chestnut in the Central States.