4 



Halsted : A new Genus of Powdery Mildews 595 



4 Appendages needle-shaped, abruptly swollen at base. Phyllactinia. 



5 Appendages not coiled or needle-shaped. Ery.rphopsis. 

 B. Appendages dichoton.ously forked at the tip. p,,o.phaera. 



6. Perithecia conta.nmg only one ascus. Microsphaera. 



7. Perithecia containing several asci. ^ 



It is not In the same group with Erysiphc and is closely asso- 

 ciated with Uncimda and Phyllactinia. 



Thus 



The Saxifragraceae, to which the Farnassia belongs, do not 

 abound in mildews and in the United States, they furnish a host^for 

 only one species of Erysiphc and two for a Phyllactima - 



Hcuchcra Americana L., is a host for Erysiphc ..;.;..;«. (Walh^) 

 and Hcuchera parvifolia Nutt., and PhUadclphus Ln.isn Pursh, 

 are recorded as bearing Phyllactima suffulta (Reb.). From the 

 standpoint of hosts it is therefore seen that the new species is asso- 

 cited with the Erysiphc and Phyllactinia. , . , • , 



I am under many obligations to Professor liurriU for his kindness 

 in examining the Parnassia mildew, and the suggestions that he 

 has made upon its peculiarities and affinities. 



The same fungus has been collected by several others. Dr. 

 Harper, of Madison, Wis., in his reply to my query concerning 

 the identity of the host, stated that he found the mildew at Wau- 

 kegan, III. during the same year it was taken at Madison. Mr. 

 F L Stevens, a former student of mine and now of the University 

 of Chicago, found the same in considerable quantity near Syra- 

 cuse N Y and elsewhere. The species is probably not rare ; but 

 one not easily seen, because of the evanescent mycelium and the 

 peculiar glabrous Parnassia leaves, as well as the inobtrusive habit 



of the host. 



