358 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



Northern California Black. These were seedling trees growing in our 

 station nursery. Vigorous, fast-growing sprouts from roots that had 

 been grafted were inoculated by puncture and gave definite positive 

 results. One observation is worthy of mention. In a single case the 

 walnut bacteriosis was observed to have spread from one of the positive 

 puncture inoculations to the nearby leaves of the tree. On these leaves 

 typical black spots appeared on the soft tissue of the leaf, as well as on 

 the veins, which were blackened. The black areas of the leaf appeared 

 to be quite characteristic and somewhat different from the effect on the 

 English walnut, in that the black, diseased and partially dried-out 

 tissue was surrounded by a narrow, yellowish-green zone just between 

 the dried-out and healthy tissue. Artificial cultures were made by 

 plating out directly from the diseased tissue and gave yellow colonies 

 which produced the characteristic growth on potato cylinders. 



Southern California Black. A single tree about five years old was 

 first used in this experiment work. Nuts were atomized in the same way 

 as with English walnuts and gave positive results. May 11, 1909, nine 

 nuts were atomized with a water solution of the walnut organism that 

 had grown on potato for six days. May 18, 1909, three nuts showed 

 positive infection and six negative. Later observations did not show 

 further infection on the other atomized nuts. Puncture inoculations on 

 nuts and shoots were also made. The punctured nuts often gave positive 

 results, but inoculations on the shoots of this tree gave negative results. 

 This may be accounted for because of the woody, hard growth. Later 

 puncture experiments on young southern California black seedlings gave 

 fine positive results and there can be no doubt as to the organism being 

 able to infect the southern variety. 



Butternut. Puncture experiment on a two-year-old seedling gave fine 

 positive results. 



Japanese Walnut. J. cordiformis and J. sieboldiana were inoculated 

 by puncture, but gave rather uncertain results. Positive inoculations 

 were produced in a few cases, but usually the lesion formed did not 

 appear typical, being simply a depressed, blackish spot without the usual 

 water-soaked zone surrounding the puncture. These later healed up 

 readily and would seem to show negative results. Results on these two 

 species are not as conclusive as could be desired : but we believe that on 

 young, vigorous, succulent growth infection could be produced. 



Hybrids. Fine positive puncture inoculations were produced on the 

 Royal Hybrid, the Paradox and Strong Hybrid (a local Paradox 

 Hybrid). These hybrids are vigorous in growth and the disease 

 develops fully as well as on either of the blacks or the English walnut. 



Walnut blight was found during the spring of 1909 on the nuts of a 



