Two serious enemies of the chestnut, if we disregard parasitic organisms, are drought and extreme cold. The winter of 1950-51 was unusually mild--scarcely cold enough to freeze the ground. The precipitation was plentiful during the winter months so that the water table was sufficient to tide over a slightly dry June and a much more serious drought in September and early October. But the latter dry period came when the nuts were matured, or nearly so. The winter of 1951-52 was again mild except for a short cold spell at the end of January, with plentiful precipitation up to the first week of June, and then a long drought with the driest July since 1944. However, the heavy rainfall of August, 8.69 inches,[19] made amends for this, and with the normal rainfall of 3.48 inches of September, prepared the trees to endure the long drought of October and early November. This serious drought,[20] which resulted in disastrous forest fires filling the air with smoke over much of the New England States, came late, however, after the nuts were nearly matured, some of the early kinds being ripe as early as the first week in September. The excessive heat of July, in which month occurred the greatest number of days on record with a maximum temperature of 90 degrees or above, was probably the chief cause of somewhat smaller results from our cross pollination work. There is evidence, indeed, that for effective fertilization, considerable heat is needed, but not the extreme temperatures that occurred during this period. In spite of the mild winter of 1951-52, the attacks of _Cryptodiaporthe castanea_ (Tul.) Wehmeyer caused considerable twig blight, especially on our crosses of _Castanea mollissimax seguini_. This is not surprising since _C. seguini_ comes from a warmer region in China, but why these attacks should occur during a mild winter is a puzzle. Evidently other factors, such as the drought of the preceding fall, entered in. Hybridization in 1951 and 1952 A total of 2400 hybrid nuts was harvested in the 1951 season and 1690 in 1952. This compares with the 1259 nuts reported for 1950. The increased production over past years can in part be ascribed to a concentration of the efforts on a fewer number of different crosses; while 103 were made in 1950, the total was 77 in 1951 and 80 in 1952. The pollinations followed the same general program in the two seasons, the emphasis being on the Chinese x (Japanese x American) hybrids. This is our most promising timber tree hybrid, and it seems worthwhile to test it on a somewhat larger scale under forest conditions. Therefore, some of the best early crosses have been repeated, new parent trees are being tried and selected hybrids intercrossed. Back-crosses to the native chestnut with the CxJA hybrids were made in an attempt to improve the form of the hybrid.