NOTES ON PERONOSPORALES FOR 1907. 
BY GUY WEST WILSON. 
Among the problems in the life history of the Peronosporales two important 
and interesting ones have received far less attention than they deserve. These 
are (1) the interrelation of meteorological conditions and the abundance and de- 
velopment of these fungi (2) the location of centers of seasonal distribution. 
While these problems have attracted the attention of a number of mycologists, 
they are of such a nature as to necessitate a series of observations extending 
over a term of years in a given locality and at the same time to require the co- 
operation of observers in localities widely separated in space and climate. To 
be of the greatest efficiency these observations, accompanied by specimens to 
properly authenticate them, should be communicated to somp one who can study 
and correlate the accumulated data. Tn this way we may be able to arrive at 
some more definite conclusions concerning the problems of oospore formation. 
As the papers on these subjects are of easy access, it is probably needless to 
review them at the present time. The most extensive series of these is by Dr. 
Halsted on the relation between the abundance of these fungi and the weather. 
These papers are based on observations mahe at , Ames, Iowa, and New Bruns- 
wick, N. J. This series began with the data for 1886 and contained seasonal 
summaries of the abundance of the various species, but as a rule not taking 
into account either the dates of appearance or disappearance or the presence or 
absence of oospores, all of which would have added materially to the value of 
the records. 
More recently another phase of the subject has been treated by Drs. Orton 
and Selby, who have been aided in their investigations of the centers of sea- 
sonal distribution by the facilities of the United States Department of Agri- 
culture. These observations have been confined almost entirely to economic 
species, such as Pseudoperonospora cubensis and PhytopJithora infestans. From 
these studies on the first species, the oospores of which have so persistently eluded 
the collector, it appears that this spore form may be elided or only produced at 
irregular intervals as a means of rejuvenation. The fungus is perennial in Flor- 
ida and from this center is carried northward by the conidia each season. 
That the same state of affairs may account for the absence from herbaria of 
the oospores of other species is not improbable, but such a theory will not 
sufiice in all instances. For example, RJiysotheca vuburnii extends from cen- 
tral New York to Alabama and may be perennial at some point in the south, 
thus dispensing with ooshores. On the other hand Rhysotheca ribicola extends 
from West Virginia through Wisconsin to Washington, with a probable north- 
ern extension of range, yet no oospores have so far been observed in America. 
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