Feb., 1907.] 
Phytophthora and Plasmopora. 
S3 
The data at hand indicate that when we have cyclar periods 
of low summer temperatures we may anticipate one or more 
seasons of Phytophthora outbreaks. A single season, or a single 
month scarcely controls; abundant moisture alone may not de¬ 
termine, as is shown in contrasting the years 1905 and 1906 in 
Ohio. In 1905 the July rainfall was 3.93 inches; that for August 
4.46 inches, while in *1906 the July rainfall was greater, 5.14 
inches, and that for August 4.72 inches; however, in 1906 the 
August temperatures rose above the optimum, the mean being 
74.6° F. 
It will be well at all times to bear in mind that hot and cold 
are relative terms; our mean summer climate is above the op¬ 
timum for Phytophthora infestans —so that in Ohio the seasons 
that are below normal are the ones which favor the fungus. In 
Maine, Nova Scotia, New Brunswick and Ireland, this may not 
be relatively the case. The mean summer isotherm of 70° F. 
crosses Northeastern Ohio, in an irregular line, entering the state 
in southern Columbiana county and emerging at Vermillion 
Erie County; a second area in northwestern Ohio is crossed by 
the same isotherm. The southern area of the state is excluded 
from the Phytophthora areas by the higher temperatures, as well 
as by the early potato crop grown there. It may be mentioned 
in passing, that very early potatoes in Georgia and Florida are 
also attacked by Phytophthora. 
From other known considerations, the foregoing suggestions 
do not appear unreasonable. The potato plant is native in cool 
regions and is most successfully cultivated in the cooler portions 
of Ohio and in states of more northerly latitude. That the de¬ 
velopment of the parasitic Phytophthora should be favored by 
analagous conditions even though limited by a much narrower 
range of temperature and rainfall than the host itself, can scarcely 
be regarded as strange. The irregularity of the outbreaks of 
Phytophthora in Ohio, is an economic difficultv in its control, 
since the public mind acts only after the fact. For Ohio it 
seems not improbable to the writer, that a succession of favorable 
or cool seasons leads to the gradual southward advance of Phy¬ 
tophthora, until established within our area; we then have one 
or more violent outbreaks of disease, followed in turn by the 
gardual disappearance of the fungus during a cycle of hot or 
dry seasons, or both hot and dry seasons. It seems very evi¬ 
dent that we do not always have it with us. 
Concerning Plasmopora Cuhensis. 
This second fungus, Plasmopora Cubensis (B. & C.) Humph., 
parasitic upon the cucumber, Cucumis sativa, and upon other 
cultivated and wild species of Cucurbitaceae, offers a contrasting 
history of development. There is a brief history given in Bulle- 
