80 



The Peeonosporales of Indiana. 



Guy West Wilson. 



The species of this order of fimgi are all parasitic upon the higher 

 plauts and are of two types known respectively as the White Rusts and 

 the Downy IMiklews. The White Rusts (AWuyo) are easily recognized by 

 their milk-white, glistening sori which are produced on the leaves and 

 stems, and even on the Ilowers and fruits of various weeds and a few 

 useful plants. The Downy Mildews produce white mould-like patches 

 upon the under surface of the leaves of various plants. To this group 

 belongs the Downy Mildew of the grape (Rhysothcca viticola (B. »& C.) G. 

 W. Wilson) which is one of our most destructive fungous diseases. 



Our knowledge of the Indiana species of the order is in a great de- 

 gree due to the work of the late Dr. L. M. Underwood, whose "List of 

 Cryptogams at Present Known to Inhabit the State of Indiana"* contains 

 a list of fourteen species of three genera on twenty-seven hosts which 

 were completely determined, besides six additional entries of hosts by 

 generic name only. As a result of a study of the material in the herbaria 

 of Dr. J. C Arthur and of the author, a paper entitled "The Phycomycetes 

 of Indiana" ^^'as prepared and presented to this Academy two years ago. 

 This paper contained four additional species of this order, one of them 

 being admitted on the authority of Dr. W. A. Kellerman. Since this time 

 Peronospora floerkeoe Kellerman has been recorded as a member of our 

 flora.t 



Within the last year the opportunity presented itself of restudying the 

 material in the herbarium of Dr. Underwood and of verifying the deter- 

 minations both of fungi and hosts. This resulted in the detection of a new 

 host and in the reduction of three of the six partially determined ones to 

 others already listed. Subsequent field work has supplemented the list 

 both of fungi and hosts imtil now twenty-two species of six genera on 

 forty -seven hosts are known from the state. 'J he number of genera 

 as compared with previous published records is doubled, the number of 

 species has been increased a third, and the list of hosts almost doubled. 



*Proc. Ind. Acad. Sci. 1893: 31-33. 1894. 

 fWilson.Torreya, 6:192. 1907. 



