Feb. 26,1917 Squash Disease Caused by Choanephora cucurbitarum 323 
an early stage in the development of a hypha from each of two conidia 
which were kept under constant observation and outlined at 15-minute 
intervals, with the aid of a camera lucida. Each successive stage is thus 
15 minutes older than the preceding one, making an interval of an hour 
between Plate 85, /, a, and Plate 85, /, e . Under favorable conditions 
of temperature (room temperature during July and August) the mycelium 
will have profusely covered a 10-cm. nutrient-agar plate within 24 hours 
and will have fruited luxuriantly. Thaxter 1 found that this fungus 
fruits abundantly in a moist chamber when cultivated on squash tissues, 
but that fructifications very rarely appear on potato agar and similar 
nutrients in tubes. 
SPORANGIAI, STAGE. 
The sporangia of C. americana , which is regarded as synonymous with 
C. cucurbitarum , was described, as has been indicated, by Moller. 2 Thax¬ 
ter states that he was never able to obtain sporangia of this organism, 
although he repeatedly cultivated it under unfavorable conditions of 
nutrition, which were held by Cunningham 3 to favor their production in 
C. infundibulifera. Such unfavorable conditions are present when the 
artificial medium is exhausted by the vegetative growth of the fungus and 
when the mycelia developed from conidia produced in artificial culture. 
When grown under artificial conditions, C. infundibulifera appeared to 
lose its vigor progressively, since no reproductive structures developed 
in cultures the third generation removed from the natural host. Neither 
were sporangia formed on the host in the natural state, a condition simi¬ 
lar to that found by the writer with C. cucurbitarum. In fact, the conidial 
stage only has been found on squashes, the other stages having all 
appeared in culture. 
Sporangia generally appear with conidial fruits, but have been formed 
alone on one set of cellulose-, bean-, and glycerin-agar plates which were 
continuously kept in the dark. Other series of cultures on the same 
kind of media when grown in darkness developed a few of both types of 
asexual spores. A different strain of fungus was used in these series. 
Certain cultures on cellulose agar, when kept in the light, developed only 
sporangia. Evidently light alone is not the determining factor in the 
formation of conidia and sporangia in C. cucurbitarum . Cunningham 3 
never obtained sporangia apart from the conidial form. 
Mature sporangia are present as early as mature conidia. They usu¬ 
ally form most abundantly at the center of the colony on plate cultures. 
Sporangia are first evident as pendent, white, globular enlargements 
The sporangium becomes separated from the sporangiophore by a glob¬ 
ular columella, which can best be seen when mature sporangia are burst 
(PI. 85, L). At maturity the sporangia are black and vary in diameter 
from 35 to 160/x. Diminutive sporangia have as few as two or three 
1 Thaxter, Roland. Op. tit. 
3 Moller, Alfred. Loc. tit. 
* Cunningham, D. D. Op, tit. 
