Feb., 1907.] Phytophthora and Plasmopora. 85 



known. Observations made by the Avriter during the years 1895 

 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 ver}^ 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 Cuhensis are not specifically known to ine, these are prob- 

 ably 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 CA'idently 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 occasionallv 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 yet 

 scarcely improbable. 



