178 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



licle which envelopes the kernel of the nut. In very hot places such 

 discoloration occurs even without visible burning of the outside of the 

 husk. This effect, however, like that of frost, is one which we believe 

 to have been largely overestimated. There is much difference in differ- 

 ent trees or varieties as to the color of the pellicle, but in good, white- 

 meated varieties we have seen nuts of perfect quality in this respect 

 produced in very hot localities in the interior of the State. Where the 

 heat is not so severe as to scorch the foliage, stunt the growth of the 

 tree, or visibly burn the nuts, little attention need be paid to this dis- 

 coloration of the pellicle so long as proper varieties are planted. The 

 chief consideration in the warmer localities should be to choose vari- 

 eties of vigorous growth, with abundant foilage, well shaded nuts and 

 thick husks. 



Hot dry weather at the time of blooming in the spring is sometimes 

 as disastrous or even more so than frost. There is little danger of this 

 in the northern part of the State, but in the south the setting of nuts 

 is sometimes seriously damaged by conditions of this sort, and indeed 

 this danger is sufficiently great to make the planting of any late variety 

 of doubtful advisability in the south. 



Specifically, we may say in regard to the climatic limitations of wal- 

 nut culture in California that wherever suitable soil and water supply 

 can be obtained and by the proper choice of varieties, the crop can be 

 successfully produced in all the counties of southern California save 

 in the desert portion, in almost all the coast counties of the State, except 

 in localities very much exposed to cold wind and fog a large portion of 

 the time, in all the valleys about San Francisco Bay and in most of the 

 country within 200 miles of San Francisco or even further. In the 

 interior valleys no definite line can be drawn where commercial walnut 

 possibilities cease, as in these warmer regions much depends upon soil 

 and moisture supply. In the mountain districts walnuts can be grown 

 almost anywhere except at the higher altitudes where spring and sum- 

 mer frosts are of regular occurrence. 



SOIL. 



A fairly heavy, deep soil with an abundance of moisture, though at 

 the same time thoroughly well drained, presents by far the best condi- 

 tion for successful walnut culture. Very little success can be expected 

 on light sandy soil subject to a fluctuating moisture supply and walnut 

 culture should not be attempted under such conditions. Trees on such 

 soil are less thrifty, less productive ? and much more subject to all the 

 troubles which affect the walnut in this State. Walnut trees on light 

 soil may flourish for a time, especially if plentifully supplied with 

 water, and in the beginning of the industry in this State it was thought 

 that such were the best conditions for walnuts. Trees grown in this 



