STUDIES IN NORTH AMERICAN 
PERONOSPORALES— V. 
A REVIEW OF THE GENUS PHYTOPHTHORA 1 
Guy West Wilson 
(With Plate 119, Containing 5 Figures) 
Within recent years our knowledge of this genus has been • 
materially augmented by the appearance of a number of important 
papers. While it is not the present purpose to present a formal 
review of all these contributions, it seems worth while to make a 
general survey of the work which has been accomplished to see 
what advances have been made in our knowledge of this economic- 
ally very important genus, as well as to take stock, to use a com- 
mercial term, with a view of learning what future lines of in- 
vestigation promise most valuable results. Perhaps nothing has 
given greater incentive to the study of this genus or made the 
progress more rapid than the discovery that these fungi could be 
grown in pure culture. The first contribution to this subject was 
by Hecke (1898) who grew P. infestans on liquid media such as 
decoctions of plums, tomatoes, cherries, and potato leaves, but 
was unable to secure a growth on solid media. Later Clinton 
( 1906) discovered that species of this genus could be grown on 
solid media other than vegetable plugs. Further discussion of 
this subject, however, is reserved for a later page. In order to 
best accomplish our object the various species will be taken up 
separately, reserving general subjects for the later part of the 
paper. 
1. Phytophthora parasitica Dastur 
The most destructive of the few really serious diseases of the 
castor bean in India is due to this fungus which has been studied 
in great detail at Pusa (Dastur, 1913). Seedlings are attacked, 
1 Previous papers of this series have appeared in the Bulletin of the Torrey 
Botanical Club as follows: I. 34: 68-84; H- 34 : 387-416; III. 35: 361—365; 
IV. 35: 543 - 554 - 1907-08. 
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