1900] BOTRYTIS AND SCLEROTINIA 383 
The disks have the usual discomycetous structure as shown 
in section (fig. 32). Asci and paraphyses are shown more 
enlarged in fig. 33. This fungus was a typical form of Sclerotinia 
Libertiana Fckl. (Peziza Sclerotiorum Lib., etc.) 
Similar infection experiments to those in the last case made 
with this material gave the same results. Diseased tissue or por- 
tions of mycelium never failed to produce the disease in healthy 
plants. No experiments have been made with ascospores in 
respect to infection. The conclusion is a safe one that Sc/erott- 
mia Libertiana is an active parasite of lettuce and, in some cases at 
least, the cause of the disease under consideration. The form 
just described, however, is far from common in greenhouses, and 
certainly does not occur in the great majority of cases of the 
“drop”, 
GENERAL CONSIDERATION OF THE CAUSE OF THE DISEASE. 
These three types cover all the cases of the disease which 
have been seen by the writer. The last occurred in but a single 
lot of plants. The second represents the bulk of the disease in 
this state. The first in its purest form was found only in the 
single lot of plants described and occasionally in a few plants in 
4 crop soon after setting. Cases are not rare, however, which 
appear to be a mixture of the first and second. Botrytis develops 
On affected plants but cultures from the most newly affected 
inner tissue give no Botrytis but characteristic growth of the 
no-botrytis form, 
The observations thus far recorded are sufficient to establish 
the following statements: : — 
: The “drop,” in the majority of cases, is a strictly parasitic 
disease and attacks the most vigorous plants. 
The ordinary Botrytis in its conidial form does not cause the 
disease €xcept in exceptional instances. 
Either of the last two forms described is able to cause the 
disease in a Strictly parasitic manner. 
The disease is spread and infection takes place most com- 
mdnly by saprophytic growth through the soil. 
