391] H. 8. 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. S. FAWCETT 



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 confined to limited geographical areas. It is hoped 



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