630 
Journal of Agricultural Research 
Vol. XXXI, No. 7 
No definite period of dormancy is necessary to prepare sclerotia 
for production of apothecia. The ecological factors of moisture, 
temperature, and light determine apothecial formation. 
Small sclerotia are especially susceptible to decay if kept too 
moist. This is one reason why it is usually much more difficult to 
obtain apothecia from S. minor and 8. intermedia than from 8. 
libertiana. 
Morphological studies, including measurements of sclerotial 
apothecia, asci, and spores, show that all of the large sclerotia, 
forms found upon the market belong to the species 8. libertiana . 
All strains of Sclerotinia under observation produced micro- 
conidia to a greater or less extent sometime during their life history. 
The amount of available food is the chief factor in determining the 
time of microconidial production. Media unfavorable for the vegeta¬ 
tive growth of the fungus induces a rapid and prolific production of 
microconidia. 
Previous to this time, as far as the writer knows, no one has ever 
observed germination of the microconidia in the genus Sclerotinia. 
In these studies the writer has been able to induce the microconidia of 
several strains to germinate. 
The experiments herein described indicate that the microconidia 
do not play an important r61e in the life history of the genus Sclero¬ 
tinia. 
Artificial infection of host plants is readily obtained by inoculation 
with sclerotia and mycelium, under favorable conditions. Moisture 
and temperature are the important limiting factors in determining 
infection. Infection may take place through unwounded as well as 
wounded surfaces. 
The more succulent plants and plant parts are penetrated most 
rapidly, while the woody tissues are a great deal more resistant, thus 
indicating that the mechanical make-up of the plant may play a part 
in resistance to Sclerotinia infection. 
Infection of freshly cut surfaces of turnip and carrot roots, by hold¬ 
ing them over “shooting” apothecia, has proved successful. An 
ascospore dilution in distilled water sprayed over lettuce leaves also 
gave positive results. 
Cross-inoculation studies show that 8. libertiana , S. intermedia , 8. 
ricinij and 8 . minor are capable of producing decay in a wide range of 
vegetables. 
None of the Sclerotinia cultures were found to be pathogenic to 
potato tubers. Beet roots were also highly resistant, although a few 
inopulations produced slight decay. 
The host range of the Sclerotinia species considered in this study 
was so wide that it is impossible to separate them on the basis of host 
infection. The decay produced (8. ncini excepted) is so similar that 
it is not until peculiarities of mycelium or sclerotial growth become 
evident that the species can be distinguished. 
S. minor produced a more rapid decay than any of the other species 
when inoculated into bean pods and other host plants and held at 
20 ° c. 
Inoculation studies as well as plate cultures show that Sclerotinia is 
able to grow and produce infection at temperatures as low as — 0.5° to 
0° C. Of all strains tested, 8 . intermedia grew fastest and produced 
most decay at this temperature. 
