PEACH DISEASES 281 



the spring rains at a time when the buds swell, and that the 

 germtube penetrates the very young leaf as it emerges from 

 the bud. This opinion is based on the following circumstantial 

 evidence: (1) lesions appear on leaves just as they are pro- 

 truding from the buds; (2) leaves from buds sprayed before 

 such buds swell show little or no infection during the season, 

 while unsprayed buds on the same tree curl badly ; (3) buds 

 sprayed after they swell, and especially after rains, show curled 

 leaves ; (4) the disease occurs only during cold, wet springs. 



From the above data it may be said that, theoretically, 

 some sort of spores are lodged by the wind or rains among the 

 hairs of the bud-scales during the late summer, and that these 

 spores remain there dormant until conditions favorable to 

 infection arise the following spring. 



The effect of the environment upon this disease is very 

 marked. This is noticed in a general way in connection with 

 the geographical range of the disease, which is most common 

 and severe in the neighborhood of large bodies of water. The 

 combination of conditions most favorable to an epiphytotic 

 of peach leaf-curl is a cold wet-period following warm spring 

 weather. Warm weather starts the buds; a cold wet spell 

 immediately following results in a saturation of the leaf-tissue 

 with water, due to a lowering of the temperature and to the 

 high humidity of the atmosphere. The buds are retarded, their 

 cells gorged with water, and their walls distended, while the 

 damp atmosphere permits spore-germination and infection. 

 As already noted, curl is most severe near large bodies of water ; 

 this is doubtless due to the increased humidity of the air in 

 these localities, and to reduced temperature in the early spring 

 as evidenced by the more frequent occurrence of fogs in such 

 regions. Heavy dews can exert but little influence on curl, 

 since the moisture and temperature factors are not sufficiently 

 pronounced nor of adequate duration to effect a response on 

 the part of the host and the parasite. Rainfall seems to have 



