614 
Journal of Agricultural Research 
Vol. XXXI, No. 7 
host plants. This is chiefly due to the fact that they are not formed 
until the host* tissue is almost totally consumed, and when plants 
reach this condition they are usually thrown away without exam¬ 
ination. 
More than 200 cultures have been under observation for 3 years, 
and all have at some time produced microconidia in greater or less 
abundance. Some strains normally produced more than others, 
but this occurred on the general stock media, potato-dextrose agar, 
which was manifestly less suitable for vegetative growth of some 
cultures than others. 
The method and time of production of these small microconidia 
leads one to suspect that they either function now as true spores in 
the life history of the fungus or that they have done so in the past. 
Working on this latter theory, the writer studied a large number of 
cultures from a wide geographical range and a large number of 
hosts, in the hope that some cultures would be in such a stage of 
adaptation or evolution that their microconidia would still be func¬ 
tioning. In all cultures collected the size, shape, and color of the 
microconidia, and the time and manner of sporulation, were essen¬ 
tially the same. - No peculiarities or distinctions of any kind could 
be noted that would indicate that one culture was more likely to be 
viable than another. 
While potato agar plus 2 per cent dextrose is a good culture 
medium for most Sclerotinia species, the addition of the dextrose 
seems to have a decidedly inhibiting influence on microconidial pro¬ 
duction. Few if any microconidia are formed in potato-dextrose 
agar cultures 20 to 30 days old, whereas on potato agar they are 
formed in great abundance at this age. On 20 per cent dextrose 
agar, a moderate growth of mycelium and a few sclerotia are pro¬ 
duced, but no microconidia are found even in cultures 30 days old. 
In contrast with these results, cultures on plain potato agar and on 
Pfeffer’s agar, held at room temperature, have formed some micro¬ 
conidia within 10 days, and plates of pure gelatin inoculated with 8. 
libertiana have developed in 10 days a very scant, loosely appressed 
mycelium which bore prodigious numbers of microconidia on the 
surface as well as on the submerged mycelium. 
GERMINATION STUDIES 
While the presence of microconidia in Sclerotinia cultures has been 
noted by many writers, no one, as far as the writer is aware, has ever 
seen them germinate. The fact that they are borne late in culture, 
and when found look like a contamination, may account for lack of 
work on this particular phase of the life history. During the past 
three years the writer has devoted a great deal of time and study to 
the attempt to determine the r6le of the microconidia in the life 
history of the genus Sclerotinia. 
The apparent de novo origin and rapid spread of watery soft rot 
in transit in such crops as lettuce, celery, cabbage, carrots, etc., has 
often suggested that some spore form was responsible for the primary 
field infection and for spreading the fungus from one plant to another 
during the transit period. A large part of this apparent spreading 
is undoubtedly due to ascospore infection from the field, but since 
even a small lesion in advanced stages of decay may bear innumerable 
