Tests were made to determine the effect of different amounts of readily available soil moisture on the growth of plums in California's dry San Joaquin Valley. In the first and second years, when there was practically no available soil moisture in the 6- to 12-ft depth, the dry-treatment plums were not significantly smaller in diameter than the wettreatment ones. But when the soil moisture was exhausted to a depth of 12 ft, the dry treatment plums were significantly smaller. The combination of Japanese plums on apricot rootstock evidently produces a deep-rooted tree, with moisture below the 6-ft depth constituting an important source of supply.

The studies reported here were done in cooperation with Dr. A. H. Hendrickson, who died before this manuscript was written.