391] HA. §. Fawcett 193 
One of the necessary conditions for the occurrence of 
melanose, when Phomopsis is present, appears to be a con- 
siderable degree of air humidity, at the season of most rapid 
growth of new shoots and of the fruit, and the absence of 
the disease in California may possibly be accounted for by 
the dryness of the air at the time when the trees are most 
susceptible to infection. This, however, does not seem to 
be a sufficient reason for the absence of melanose in the 
southernmost parts of Florida and Cuba. 
Edgerton has recently emphasized the apparent bearing 
of temperature conditions on the occurrence of certain plant 
diseases in sub-tropical climates. He is convinced that the 
absence of anthracnose in beans grown at certain seasons in 
Louisiana is due to the fact that the average temperatures 
for those seasons are above the optimum for the growth of 
the pathogenic fungus. If this is true in the case of anthrac- 
nose it may also be true in the case of melanose. The first 
requirement for a test of this suggestion is, of course, some 
definite knowledge concerning the temperature relations of 
Phomopsis itself, and experimentation is now in progress’ 
in this direction. 
PRELIMINARY NOTE ON THE RELATION OF TEMPE- 
RATURE TO THE GROWTH OF CERTAIN ~ 
PARASITIC FUNGI IN CULTURES 
By H. 8. Fawcerrr 
Interest in the temperature relations of plant growth is 
rapidly increasing, and, as improved methods become avail- 
able, increasingly precise studies are being made of the in- 
fluence of temperature upon growth as variously measured. 
The study upon which the writer is at present engaged aims 
to compare the temperature-growth curves for cultures of 
a number of fungi that produce diseases of citrus trees and 
that are confized to limited geographical areas. It is hoped 
18 
