Feb., 1907.] 
Phytophthora and Plasmopora. 
85 
known. Observations made by the writer during the years 1S95 
to 1906 inclusive, show that this Plasmopora makes its appear¬ 
ance upon field cucurbits in northern Ohio very much earlier 
in a warm season than in a cold one; it has never been collected 
earlier than August 10th in the vicinity of Wooster (August 3rd, 
Marietta, O.) and it is sometimes as late as Sept. 10th, and, pos¬ 
sibly, altogether absent. The cool seasons of 1902-1905 have 
brought very late or no development of Plasmopora in Ohio, 
while the warm August of 1906 witnessed an early development 
near Wooster, August 11-14. These dates but repeat those of 
1898 and 1897. While the optimum temperatures of Plasmo¬ 
pora Cubensis are not specifically known to me, these are prob- 
ablv near the summer maximum in Ohio. Seeking to get fuller 
data upon the occurrence of this fungus in the United States, the 
writer through the co-operation of Dr. T. B. Galloway, U. S. 
Department of Agriculture, mailed letters of inquiry to most 
mycologists and pathologists of the United States in 1898. The 
replies elicited the fact from Prof. H. H. Hume that the Plas¬ 
mopora evidently survives the winter upon wild cucurbits in 
Florida and from other data, the same appears at successively 
later dates northward as the season advances. At that time 
the writer suggested the possibility that the Plasmopora upon 
cucurbits is propagated northward each season by means of its 
conidia; a possibility that may now be regarded as a probability. 
In addition to this the disease is occasionally domiciled in forcing 
houses and there survives. May this northward advance each 
year, like that of migrating birds, be the true explanation of its 
recurrence with us? The matter is difficult of proof but vet 
scarcely improbable. 
