418 . F. M. Rolfs 



from infected Elberta twigs. During 1908 the shot-hole condition de- 

 veloped on the foliage of nearly all these trees, and cankers were more or 

 less plentiful on the twigs of many of them. Trees of this sort, when set 

 out, not only grow poorly, but also serve as centers from which all neigh- 

 boring trees become inoculated. In the course of the past five years 

 several cases have come under observation in which a few infected trees 

 from a poorly kept nursery were mixed in large shipments of clean trees. 

 The infected trees served after planting as inoculum centers, and three 

 years after planting every tree in these orchards was diseased. 



In a careful inspection of peach and plum trees in various sections of 

 South Carolina, not a single case of the disease was observed on isolated 

 seedling peach and plum trees; yet the organism was repeatedly collected 

 on the budded peach and Japanese varieties of plum in both family and 

 commercial orchards, indicating that the nurseries are largely responsible 

 .for the spread of the pathogen. 



Incubation. — The period of incubation varies more or less, depending 

 on temperature, moisture, and method of inoculation. The period is 

 about the same on all four kinds of trees. In some cases, however, it 

 appears to be slightly longer on leaves and twigs of apricot and plum than 

 on those of the nectarine and the peach. 



In experiments in which the organism was suspended in water and ap- 

 plied to the leaves and fruit with an atomizer in warm, moist weather, the 

 period apparently varied from seven to fifteen days, but in cold weather 

 the period was prolonged to twenty and even twenty-five days. When 

 water containing the organism was apphed in warm weather to the lower 

 surface of the leaf and to the fruit by means of a pipette dropper, and was 

 spread by gently rubbing leaf or fruit between the thumb and the fingers, 

 signs of disease appeared on the leaves in from five to seven days and on 

 the fruit after seven or eight clays; in cold weather, however, the period 

 was considerably extended on both leaves and fruit. On the twigs, con- 

 siderable difficulty having been experienced in obtaining results with the 

 spray and rubbing method, a hypodermic syringe was used. The needle 

 was inserted just beneath the cuticle and a small quantity of water con- 

 taining the bacteria was forced into the tissue. Very uniform results 

 were obtained in this way. The period of incubation following these 

 inoculations varied from four to ten days, depending largely on the tem- 

 perature and on the number of organisms forced into the tissue. In the 



