1914] 
COOLEY—SCLEROTINIA CINEREA 317 
content of these restraining agents. The question of the acid 
relation of the host tissue is one of fundamental significance 
and one that is worthy of considerable investigation; it is im- 
portant to know to what extent acidity may be a limiting factor 
in parasitism. 
A case in which a certain acid content is favorable for the 
fungus is developed by Falck (22). He finds the acidity of the 
substrate to be a conditioning factor for the growth of several 
species of Merulius. In this connection the author observes that 
Coniophora, in particular, acts to pave the way for Merulius in 
that the former organism renders the nutrient substrate deci- 
dedly acid, and thereby provides favorable conditions for the 
germination of the spores and the subsequent growth of myce- 
lium and fruit bodies of Merulius. In connection with the in- 
vestigation of the plum disease here discussed it would be well 
to know if the acidity of the fruit changes during the progress of 
its growth, and if so in what direction. It is also essential to 
know whether or not a change in the acidity of the host can 
account for the fact that ripe fruit is more susceptible to the 
disease than green fruit. Some experiments were planned, 
therefore, to determine to what extent the acidity of the host 
influences the attack of the parasite, and also to investigate 
what effects, if any, the fungus has with respect to the acid 
content of the host. 
In order to determine the changes in acidity which take place 
during the growth of the fruit (plums), several analyses for acid- 
ity were made at intervals during the summer. The plums for 
all of the analyses were taken from the same tree, a known 
weight of pulp being ground up in a mortar and squeezed 
through muslin. The acidity was reckoned in the number of 
ec. of N/10 NaOH required to neutralize one gram of plum 
pulp. Тһе results were as follows: 
June 28, 1 gram plum pulp required 0.66 cc. N/10 NaOH for 
neutralization, 
Aug. 2, 1 gram plum pulp required 2.12 cc. N/10 NaOH for 
neutralization, 
Aug. 19, 1 gram plum pulp required 2.46 cc. N/10 NaOH for 
neutralization, 
