82 



The Ohio Naturalist. 



[Vol. VII, No. 4, 



ment of the disease is checked. This explains why the potato 

 blight fungus seldom occurs to any extent in sections where the 

 mean or normal daily temperature exceeds for anv length of 

 time 77° F." 



I am unable to state at this time the basis upon which the 

 above statements rested at the time, but with certain modifica- 

 tions they will fully cover Ohio conditions. Recalling that the 

 years 1883 to 1886 inclusive, and 1903 to 190G in Ohio, were 

 periods of prevalence for Phytophthora infcstaus in Ohio, we may 

 glance at the weather conditions for these periods and compare 

 with the means of the past 24 years. It seems only necessary 

 to consider the months of June, July and August. Unfortunately 

 our data do not extend back further than 1SS3. 



I have prepared a table showing the mean summer tempera- 

 tures and mean rainfall in Ohio for 1883 to 190G: 



Mean Summer Temperatures and Rainfall in Ohio 1SS3-19U0 



The summer temperatures for the years 1S83 to ISSG, taken 

 as a whole, were decidedly below the normal. The same is true 

 for the summer months for the years 1902 to 1906, excepting the 

 month of August 1906. 



