414 Witson: NortTH AMERICAN PERONOSPORALES 
late, 20-40 x 14-25; odspores spherical, yellowish, watery- 
papillate, 30-42 4, maturing in the decaying leaves. 
This is one of the most important pests of the truck farmer. 
Its adaptibility to almost any cultivated species of Cucurbitaceae 
and the comparative immunity of the native species, especially in 
the more northern states, makes it a pest which is most destruc- 
tive in regions where Cucurbitaceous vegetables are cultivated in 
commercial quantities. Its favorite hosts appear to be the cucum- 
ber and melon. It has been suggested that the fungus spreads 
from south to north each season, and in proof of this theory are 
cited the perennial character of the mycelium in Florida and the 
records of the distribution of the pest in the southern and eastern 
states in recent years.* It has also been suggested that hot-house 
culture of the hosts assists in scattering the disease, at least in the 
immediate vicinity. It is not impossible that both these factors 
enter into the distribution of the fungus, while the researches of 
Rostewzew, who found the immature oospores in the partially de- 
cayed leaves of infested vines, tend to establish the probability 
that odspore-production also plays a most important part in the 
persistency of the pest in infested areas. By the first two means 
suggested, the distribution of the fungus would of necessity be 
confined to those regions which could be reached by summer 
migration and in which hot-house cucurbits were produced. The 
third method of passing the winter, in addition to the first two, 
accounts for the occurrence and persistence of the disease in places 
which, according to the two preceding theories, should be immune 
from the pest. The problem presented is one of great scientific 
interest and of a not inconsiderable financial importance to certain 
sections of the country. 
On CucurBITACEAE : 
Bryonopsis lacunosa erythrocarpa Naud., Ohio, Selby. 
Citrullus vulgaris Schrad., Louisiana, Langlois 1122. 
Coccinia indica Wright & Arn., Ohio, Sedby. 
Cucumis angulatus Forsk., Ohio, Sedéy. 
Cucumis Melo \.., Ohio, Selby. 
Cucumis odoratissimus Moench, Ohio, Se/by. 
* Bull. S. Car. Agr, Exp. Sta. 116: 7, 1905. 
