50 Natural History Bulletin. 



1 6. P. OBDUCENs. — Schroeter. 



Impatiens -pallida. Decorah. 



17. P. PARASITICA. — Till. 



On Brassica nigra, Sisynibrittm cancscens, Nasturtium 

 palustre, Capsella bursa-p^istoris, Lcpiditmi virgini- 

 aini. Ames. Iowa City. 

 Dentaria laciniata. Decorah. 



Very common in the spring on Cruciferae. In the case 

 of Nasturtium, Capsella and Lepidium, it covers the 

 under surface of the seedHng leaves with a dense 

 white fleece. Conidia were found on the ripe pods 

 of Brassica. In Sisymbrium the stems and pedicels 

 were very much distorted. 



18. P. POLYGONi. — Thucm. 



On Polygonum aviculare. Iowa City. 



On P. dumctorum, var. scandens. Ames, (Halsted). 



19. P. POTEXTILLyE. — DeBy. 



20. P. PYGM^A. — Unp-er. 



On Anemone dichotoma. Ames. 



This species is peculiar in having short, stout conid- 

 iophores, with very short pointed branches for the 

 attachment of the spores. 



21. P. SORDIDA. — Berk. 



On ScropJuilaria nodosa. Ames, Iowa City, Decorah. 



22. P. TRiFOLiORUM. — DeBy. 



On Vicia americana. Ames, Decorah. 

 On Astragalus canadensis. Ames. 



23. P. URTicAE. — DeBy. 



On Laportea canadensis. Ames, Aug., 188S. 



24. P. viTicoLA. — DeBv. 



On Vitis riparia. Ames, Iowa City, Decorah. 



On cultivated grapes. Ames (Halsted), Iowa City, 



(McBride). 

 During the dry seasons of ""^6 and '87 the "grape mil- 



