Feb. s 6 , 1917 Squash Disease Caused by Choanephora cucurbitarum 325 
is increased until the terminal walls of the suspensors tend to be in the 
same plane (PI. 86, £), and the suspensors appear to support it from one 
side. Meanwhile the exospore has thickened, become dark brown in 
color, and the oil globules have fused to make one large globule, which 
occupies one-third to one-fourth of the volume of the ripe zygospore. 
Zygospores vary in size from 50 to 90 /x in the longest diameter. . 
Mature zygospores were first observed in nutrient agar cultures 48 
hours old which had been planted with conidia taken from squash 
flowers. They appeared, however, in only a small number of isolation 
cultures prepared in this way. They are formed embedded within the 
agar and on its surface and can be seen with the unaided eye as numer¬ 
ous black specks when the isolation plates are held against a white back¬ 
ground. Conidia and sporangia are always present in these plates. All 
attempts to germinate these zygospores have thus far met with failure. 
Furthermore, all attempts to determine the conditions necessary for 
zygospore formation have been futile. Curiously, no zygospores ap¬ 
peared in subcultures from cultures in which zygospores were present; nor 
have they ever been noted in culture except when the conidia for making 
these cultures were taken directly from the host plant. It was presumed 
that this might be due to a loss of vigor in artificial culture. It will be re¬ 
called that cultures of C. infundibulifera three generations removed from 
the natural host failed to form asexual spores. No such failure to form 
conidia and sporangia appears to occur in C. cucurbitarum , since it has 
been grown for 15 generations with no resultant decrease in the luxu¬ 
riance of its asexual fructifications. Numerous cultures have been 
obtained from single conidia and sporangiospores with the view of 
determining whether in this species zygospore formation was condi¬ 
tioned by heterothallicism. Thus far, however, no evidence of this 
separation of sexes has been found. 
When material for studying zygospore development was at hand, the 
press of other duties prevented the making of a detailed study of the 
process. Subsequently, it has been impossible to develop zygospores. 
However, several blocks of agar containing zygospores were fixed, sec¬ 
tioned, and stained. Unfortunately, only a few of the stages were ex¬ 
hibited in these sections. Plate 86, A, represents an early stage in which 
the gametes have been separated from the suspensors. Gametes, sus¬ 
pensors, and vegetative mycelium (Pi. 86, D) are found to be multinu- 
cleate. It is hoped subsequently to be able to furnish an account of the 
conditions necessary for zygospore formation and of the cytological 
phenomena accompanying this process. 
Since no complete account of all of the spore forms of this organism 
has ever been given, it seems desirable to present herewith a brief tech¬ 
nical description, together with its synonomy and the known list of hosts. 
