A SEKI0US LETTUCE DISEASE. 
117 
abundance, Fig. 22. Attention has been called elsewhere, 18 to the im¬ 
portance of mycelial crowding as a stimulus. 
Fig.’ 22. —Sclerotia produced in culture upon corn meal wetted with apple broth, showing rows 
of sclerotia where colonies met. 
To determine the length of time necessary for sclerotia to mature, 
for germination, a large number of sclerotia was taken from corn meal 
cultures and air dried for a few days. They were then planted in 
pots of sterilized soil at periods of a week apart. At each of these 
plantings old sclerotia, that were known to be mature, were also planted 
as controls. All of these grew, even those which were picked and merely 
air dried for a day or so showing as vigorous germination as did the 
old sclerotia. It thus appears that sclerotia are mature as soon as 
formed and are ready to germinate at once if favorable conditions 
obtain. 
Attempts were made to determine the length of life of sclerotia 
under laboratory conditions and lettuce bed conditions. In the labora¬ 
tory sclerotia were stored in ordinary room temperature, one lot in the 
dark all the time, another lot alternately in the light and dark of day 
and night, a third lot was kept wet all the time. Three similar sets were 
kept in the incubator room (temperature 37 degrees). At the end of 11 
3 
