PEACH SCAB AND ITS CONTROL, 21 



being less than 2° C; the optimal, between 20° and 27° — about 25°; 

 and the maximal, slightly above 32°. 



RELATIONS OF LIGHT. 



Numerous drop cultures of the type just mentioned were incu- 

 bated comparatively m strong diffuse light and in darkness at 

 temperatures ranging from 20° to 25° C. Normal development 

 resulted in aU cases, the differences in Olumination appearing to have 

 no marked influence on germination. 



PATHOGENICITY. 



Relative to an inoculation experiment with Cladosporium car- 

 popTiilum from culture, Chester (1897, p. 63) makes the following 

 statement : 



Sown on the uninjured surface of green peaches, a slight growth resulted, in only 

 a few cases simulating the natui'al infection; it was evident, however, that the peaches 

 were at that stage of their development not in condition for the best development of 

 the fungus on their surface. When the inoculation of the peach was accompanied 

 by a puncture, the fungus developed and produced spots like those seen in nature. 



Thus, no defuiite data are given concerning the source of inocula- 

 tion, the method of experiment, or the results obtained, and no 

 mention is made of controls. Furthermore, the writer's experi- 

 ments, reported below, show that punctures are not essential to 

 abundant infection, and that the utmost care is necessary for the 

 attainment of rehable results from fruit inoculation with Cladosporium 

 carpopMlum in sections where scab occurs abundantly. This experi- 

 ment, therefore, does not justify conclusions. 



Aderhold (1901, p. 657) conducted a cross-inoculation experiment 

 with Cladosporium cerasi and C. carpopMlum. The results, however, 

 were admittedly inconclusive. 



The writer (1914a, 1914b) reported, in a preliminary way, positive 

 results from inoculating peach fruits, twigs, and leaves with Cladospo- 

 rium carpopMlum from various sources. The results of these and 

 further experiments are given more completely below. They com- 

 prise, so far as the writer has been able to ascertain, the only authentic 

 records of positive results from inoculation experiments with this 

 fungus. 



Fruit Inoculations. 



Preliminary experiments and observations of two seasons showed 

 clearly that under field conditions where the disease occurs abun- 

 dantly, successful fruit inoculations with peach scab must be planned 

 to overcome the following difficulties: (1) The abundance of natural 

 infection, rendered especially baffhng by the long period of incuba- 

 tion of the fungus, and (2) the difficulty of obtaining at will condi- 



