12 
N. C. Experiment Station 
although under favorable conditions older plants were in a few instan¬ 
ces attacked. His investigations furthermore led him to assert that 
infection does not take place through the stomates, but by penetration 
of the epidermal cell walls. The results of direct infection of lettuce by 
ascospores of Sclerotinia libertiana led Stevens and Hall (24) to con¬ 
clude that it seldom, if ever, occurs, and that the fungus becomes para¬ 
sitic only after it has maintained itself for a time, as a vigorous sapro¬ 
phyte. Because of the fact that infection begin on the stems at or near 
the ground level in the case of stem rot of clover, it is believed that the 
vegetative mycelium is responsible for the disease and that little disease 
results naturally by direct infection with ascospores. 
Infection Experiments 
Several series of artificial inoculation tests have been made during 
the past two years. These involved plants of crimson clover, red clover, 
and lettuce grown within the greenhouse in flats or in beds, and crimson 
clover, hairy vetch, Yicia villosa, and lettuce grown under field con¬ 
ditions. Inoculation in the greenhouse was accomplished by introduc¬ 
ing the appropriate organism from cultures on steamed rice or steamed 
corn meal or from diseased plant parts into the soil near the collar of 
the plants. Wilting was apparent within 8 to 10 days in the case of 
lettuce, crimson clover, or red clover, when either Sclerotinia trifoliorum 
or S. libertiana were employed. Practically all of the inoculated plants 
succumbed, irrespective of whether the inoculum consisted of pure cul¬ 
tures or of decaying plant tissues. 
During April, 1917, plants of crimson clover and vetch five to eight 
inches in height were inoculated in the field by parting the stems and 
placing at the center of the plant fragments of lettuce affected with 
drop, S. libertiana. The plants thus inoculated were then lightly covered 
for 36 hours with a newspaper weighted at the corners. Five days after 
inoculation many of the younger stems near the center of the rosette 
were dead and their tissues involved in decay. The copious superficial 
mycelial growth was like that of the lettuce drop organism- Within 
twelve days even the larger stems had begun to wilt. Stem rot had never 
been present in this field and only the inoculated plants were affected. 
Furthermore, lettuce plants in another field were inoculated on the same 
day by inserting diseased lettuce leaves into the heads. These plants 
were in an advanced stage of drop a week later. 
During November, 1917, crimson clover in the field was inoculated by 
placing in the soil pure cultures on corn meal of S. trifoliorum and of 
S. libertiana. Four weeks later circular areas eight to ten inches in 
diameter in which all of the plants were dead, had formed around the 
