THE MONTHLY BULLETIN. 429 



greatest limiting factor for walnut production in the principal nut- 

 growing countries. 



It is a well known fact that in the vegetable kingdom closely related 

 species suffer in different degrees from the attacks of the same parasite. 

 This difference in resistance is as often marked among different vari- 

 eties of the same species as between the species themselves. There is a 

 great deal of difference in the amount of blight prevalent at the present 

 season in the different walnut-growing sections. The absence of blight 

 is not necessarily an indication of immunity. Again, the immunity 

 from blight of a particular tree for one season may be followed by more 

 or less prevalency of blight the next season. This must be tested out 

 through a number of years before any varieties can be pronounced 

 resistant to this disease. The observations must also be carried out in 

 different localities, as certain sorts seem to behave differently on dif- 

 ferent soils, and growing under different climatic conditions. 



Some varieties seem to avoid the blight the majority of the seasons, 

 and really have little or no resistant qualities when the seasonal condi- 

 tions for the most favorable spread of the disease happen to coincide 

 with the season of the susceptible growth of the plant. An example of 

 this is seen in the Eureka variety the present season. While this 

 variety has maintained a reputation during a majority of seasons 

 for freedom from blight, during the present year the Eureka is badlv 

 diseased in certain sections of Orange County. This may perhaps be 

 explained by the prevalence of damp, cloudy weather for about a week 

 or ten days along the first of May. when this variety was in full bloom. 

 In one grove under observation the trees Avere thought to have lost at 

 least 50 per cent of their blossoms soon after blooming. At the present 

 time on these same trees 32 per cent of the nuts, as they are on the trees 

 at present are afflicted with more or less blight. To "be sure, some of 

 these wall likely mature, but the appearance of blight on nearly one- 

 third of the crop shows that this variety has very little actual resistant 

 power against walnut blight ; its freedom from disease in the past has 

 no doubt been due largely to its dormancy during the most favorable 

 weather conditions for the spread of the disease. 



The field for the selection of blight-proof varieties must necessarilv 

 be in the sections very favorable to blight. A tree which has only 

 10 per cent blighted nuts, in an orchard which averages from 70 per 

 cent to 80 per cent may really be more resistant to blight than a variety 

 which appears to be positively free from the disease, growing among 

 trees which are only 15 per cent to 20 per cent blighted. In the making 

 of any observations and selections, therefore, it is quite as important to 

 know the amount of blight on the surrounding trees and the grove as a 

 whole, as it is to know the prevalence of blight on the selected indi- 

 vidual. The extreme variation of different seedling trees in their sus- 

 ceptibility to this disease is well illustrated in .some of the following 

 observations whicli were made the present year: The percentages which 

 follow the varieties named were determined by counting at least 100 

 nuts on a tree just before the nuts began to drop. In a seedling grove 

 in the Whittier district about 300 trees were counted, 100 nuts on a tree. 

 The individual trees varied from 2 per cent to 85 per cent blighted nuts 

 while the grove as a whole averaged 25 per cent. There were at least a 

 dozen or fifteen trees in this grove which were blighted less than 10 per 



