9 
Peronospora polygoni, Thum., is rare on Polygonum dumctorum . 
Mr. Hitchcock found the mildew upon P. aviculare , at Iowa City in 
May of 1887, but it was not at all common. It was abundant upon P. 
convolvulus in July of the last season. 
Peronospora alta, Fckl., has been almost entirely absent from 
Plantago major , for the last three years. In 1885 it was one of the 
easiest of the Peronosporas to obtain in quantity. 
Peronospora trifoliorum, DBy., has heretofore been one of our 
most common species upon Astragalus Canadensis , and especially on 
Vicia Americana. Upon the latter two years ago it was so abun¬ 
dant as to almost destroy the host in whole patches. It was found in 
1887 only after diligent search in the moistest places where the vetch 
will grow. It again appeared in 1888 but in milder form than before 
the dry years. 
Peronospora euphorbia, Fckl., is a species which quickly dis¬ 
appears in times of drought. It is not uncommon on Euphorbia mac - 
ulata , in a wet season, but rare indeed in 1887. The usual amount 
was met with in 1888 noticeably dwarfing the small leaves of the host. 
Peronospora leptosperma, DBy., was common in 1885 on both 
Artemisia biennis and A. Ludoviciana. During 1887 it was met with 
in only a few places on A. biennis , growing in moist spots near excava¬ 
tions along a railroad track. Last season found it abundant again. 
Peronospora sordida, Berk., is a good illustration of the influence 
of moisture upon the development of Peronosporew. The host Scrophu- 
laria nodosa is a common plant on the banks of streams, especially 
where the surface is without sod. In 1887 the mildew was abundant 
in only one place—a bend of a stream where the host grew close to the 
water and could obtain moisture freely. It was not at all uncommon 
during the last growing season. 
Peronospora lopiianthi, Farlow, on Lophanthus scrophularicefo- 
lius , is a rare species in Iowa and was met with only in 1887. 
Peronospora graminicola, Schrcet., which was abundant in 1886 
upon Setaria viridis , transforming the inflorescence of the grass into 
strange shapes, was far less common during 1887. Last autumn it in¬ 
fested the foxtail quite generally and appeared to some extent upon 
the Hungarian grass. This new parasite may do much mischief in the 
i'u t ure. 
Peronospora calotiieoa, DBy., is not rare upon species of Ga¬ 
lium. In October, 1S87, seedling plants, which had come up in a rich 
mold since the September rains, were badly infested. This is a good 
illustration of fresh, growing tissue being favorable for the development 
of Peronosporece. 
The genus Cystopus has four species common to Iowa. 
Cystopus candidus, Lev., like Peronospora parasitica, is confined to 
the Crucifercc , and also like it lives over the winter within the tissue of 
the seedling plants. There was an abundance of the Cystopus on Shep- 
