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 OP LIGHT. 
Numerous drop cultures of the type just mentioned were incu- 
bated comparatively in strong diffuse light and in darkness at 
temperatures ranging from 20° to 25° C. Normal development 
resulted in all cases, the differences in illumination appearing to have 
no marked influence on germination. 
PATHOGENICITY. 
Relative to an inoculation experiment with Cladosporium car- 
popTtilum 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 natural 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 definite 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 reliable results from fruit inoculation with Cladosporium 
carpopJiilum 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. carpophilum. 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 carpophilum 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. 
Prehminary 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 baffling by the long period of incuba- 
tion of the fungus, and (2) the difficulty of obtaining at will condi- 
