532 Wisconsin Academy of Sciences, Arts, and Letters. 
Late in December, about two months after it was first 
brought into the greenhouse, the mildew began to spread over 
other cucurbit plants, mainly vines of various cultivated 
gyurds. At first the mycelium was very scanty on these vines 
and very few conidia were produced. Later, however, the 
mycelium spread rapidly, forming conidia abundantly. 
By growing at intervals young cucurbit plants, mainly 
squashes, and inoculating them, the mildew has been kept grow¬ 
ing in the greenhouse since its first introduction. 
.Various species of mildews have been reported as occurring 
On cucurbits. Sphaerotheca castagnei Lev. has been reported 
upon Cucumis sativus by Beck (3), Bucket (7, 8), Von Thii- 
men (36), and Voss (38) ; upon Cucurbita maxima by Ca- 
vara (6) ; upon C. Pepo by Beck, Von Thiimen and Wettstein 
(39) ; upon Cucurbita sp. indet., by Brunaud (5), Jaczewski 
(11), Lambotte (12), Leveille (13), and Passerini (21). 
Erysiphe polygoni DC. has been reported upon Cucumis sati¬ 
vus by Magnus (14) and Schroeter (35), and upon Cucurbita 
sp. indet. by Berlese and Peglion (4). Erysiphe cichoracea- 
rum DC. has been reported upon Cucumis sativus by Hum¬ 
phrey (10), and upon Cucurbita pepo by Salmon (23). The 
latter says: “It is, of course, possible that more than one spe¬ 
cies of Erysiphe occurs on these host plants [various cucur¬ 
bits], but in this case it seems more probable that the fungus 
has been named constantly Sphaerotheca castagnei merely be¬ 
cause this species was originally recorded on these host plants, 
and it would be very interesting to know if any example with 
perithecia of Sphaerotheca really exists.” 
Although the conidial stage of the mildew, known as Oidium 
erysiphoides, is very common upon cucurbits, especially in 
greenhouses, apparently perithecia are rarely formed. The 
vines where the mildew was first found were carefully exam¬ 
ined, but no perithecia were observed. The infected plants 
in the greenhouse were also closely observed for the sexual 
fruits of the mildew. Hone were found, however, until No¬ 
vember 6, 1905, over a year after the first introduction of the 
mildew into the greenhouse. At that time perithecia were 
