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UNIVERSITY OP CALIFORNIA EXPERIMENT STATION. 



enough has been done to show that nuts in such late trees are compara- 

 tively free from the disease. Some of these late varieties are described 

 in another part of this bulletin. 



Immunity. Certain trees are some times spoken of as being immune 

 to the blight, but while there is probably no such thing among walnuts 

 as absolute freedom from this disease, where conditions are favorable 

 for blight infection, yet some trees do show quite a marked resistance, 

 and, if otherwise desirable, are given precedence in new plantings on 

 this account. (See Eureka, etc.) It may be that in certain localities 

 there is no blight, but this probably is not due to any immunity that 

 the trees possess but is rather the effect of climatic conditions or due to 

 the fact that the specific organism has not yet reached this particular 

 locality. 



Isolation. Pure cultures of the walnut bacteriosis are most easily 

 obtained from recently diseased nuts, although they have also been 

 secured from diseased leaves, old lesions and young blighted shoots, as 

 well as from certain flies that are quite abundant about walnut trees 

 during the period of infection. 



Table shoiving dates and results from various attempts to isolate the walnut blight 

 organisms from diseased tissue. 



