340 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



the following one showed comparatively little of the disease. It will be 

 instructive to observe a few of the reasons for this difference. 



The winter of 1906 and 1907 was a rather wet season, there being 

 about 20 inches of rainfall in the vicinity of Los Angeles. The spring 

 opened very early, some walnut trees beginning to show leaves during 

 the last week in February. Some of our preliminary inoculation work 

 was done at this time, February 22d. Small nuts appeared early in 

 March, and on March 7th we inoculated our first small walnuts for 

 bacteriosis. It is safe to say that the season was at least three weeks in 

 advance of the average time of blossoming, which gave a longer period 

 favorable for infection to take place. This is an unusual situation, and 

 has not been repeated. 



The winter of 1907 and 1908 was a dry winter, there being about 

 twelve inches of rainfall in the regions around Los Angeles. The earlier 

 trees began putting out leaves about April 1st. Too much importance 

 should not be given to the difference in the amount of rainfall of the 

 two years, as its relation to the amount of bacteriosis is exceedingly 

 doubtful. 



Another favorable condition of 1907 was the cloudy weather during 

 March, April and May, the time of year when the bacteriosis is most 

 active, as compared with the conditions of the same period during the 

 following year. This is well shown in the following table compiled 

 from data very kindly furnished by Mr. A. B. Wollaber, the local fore- 

 caster of the United States Government Weather Bureau at Los Angeles. 

 It is well known that sunlight is fatal to most kinds of bacterial germs 

 and the walnut bacteriosis is no exception to this rule. The table shows 

 that the nuts during the spring of 1908 had a much greater amount of 

 sunshine during their first three months of growth than did those of 

 1907 during the corresponding three months. May not this in some 

 measure be the reason for the difference in the amount of this disease 

 during these two years? 



