52 
IOWA ACADEMY OF SCIENCE 
The Downy Mildews. (Peronosporeae) . This group of fungi has been studied 
more carefully with respect to meteorological conditions than any other kind. 
The years 1895, 1903 and 1905 were particularly favorable for their development. 
It will be seen from the weather conditions that we had during growing a great 
deal of moisture accompanied by high temperatures. 
The year 1903 will be remembered as very destructive to the potato. In 
addition to the potato rot fungus {Phytophthora infestans) the grapevine mil- 
dew (Plasmopora viticola) was abundant. 
Prof. Guy West Wilson whose work on the Peronosporales, for 1907, has been 
noted in another place, says: 
''Plasmopora Halstedii (Parlow) 
This species was first observed July 29th in the vicinity of Greencastle, 
Indiana, where a few infected leaves were found on one or two plants on Bidens 
frondosa. By August 13th the fungus was fairly abundant in this locality and 
by the 27th of that month scarcely a plant remained uninfected in all the 
Indiana localities visited. The infection was as complete as any seen during 
the season, all the leaves being affected and the lower ones killed outright, but 
no oospores were found. A sihgle clump of Erigeron annuus was also found 
infected.” This species was common in Ames in August and September. 
"Plasmopora viticola (B. & C.) 
This species was quite abundant on both wild and cultivated species of 
Yitis when they were first examined in July. Conidia were collected on leaf, 
petiole, tendril, and young twigs. In some vineyards the disease was respon*. 
sible for heavy loss of fruit but none of the diseased berries were examined 
for oospores. Among the twelve specimens collected one was upon seedlings of 
cultivated grapes.” 
The Grape Vine Mildew was abundant in Ames and in northeastern Iowa 
in June and July. It was not abundant later in the* season. Spring shoots of 
the wild grape were badly diseased. 
Premia lactucae Regel. Mildew of Lettuce. 
Prof Wilson states that this fungus was “collected on Lactuca canadensis 
in Hamilton and Putnam counties, Indiana, between July 23d and August 3d. 
All this material had the appearance of being quite old and indicated that the 
conidia had been produced for some time past. Of the three specimens collected 
none contained oospores.” It was abundant on wild lettuce in June in the 
vicinity of Ames, none, however, was observed on the cutivated lettuce. 
Peronospora alta Fuckel. 
Prof. Wilson did not report it as common in Indiana, but it was abundant 
in Ames in June in 1907, where thousands of leaves were diseased. It was not 
abundant in Ames in 1908. 
Peronospora parasitica (Pers.) Fries. Downy Mildew of Mustard. 
This fungus was abundant during the month of May and June, 1907, in Ames, 
later appearing on other hosts. It was not common in 1908. Prof. Wilson says 
concerning this fungus: 
“During the early spring in New York this fungus attacked great numbers 
of seedlings of Lepidium virginicum but soon run its course. The previous 
summer the fruiting and infiorescence was frequently destroyed during mid- 
summer, but this season no such attack was noted oefore reaching Newark, 
Delaware, where the fungus was evidently just making its appearance. The 
same host was found sparingly affected in Indiana. Here a single clump of 
