374 BOTANICAL GAZETTE [JUNE 
were produced abundantly on affected plants and in cultures. 
These were very small and insignificant, but numerous in every 
case. 
Humphrey’s conclusions that the disease is caused by Botry- 
tis vulgaris appears to have been generally accepted by all who 
have written concerning this disease. It is very probable that 
in some of the citations given above the disease was not the 
real stem rot or “drop,” but simply a case of Botrytis on the 
leaves, as often occurs on all kinds of plants when growing 
poorly or under unfavorable conditions. But in many of the 
references it is evident that the typical stem rot was found and 
ascribed to Botrytis. In no case was any extended investigation 
made. Early in the writer’s study of this disease it became evi- 
dent that whatever the cause might be, many cases occurred in 
which no Betrytis could be found, although otherwise the 
disease was very typical. Extended observation of a very large 
amount and variety of material from various sources has shown 
the existence of what may be called three forms of the typical 
disease. This excludes some other lettuce troubles of a more or 
less similar nature. 
THe BOTRYTIS TYPE. 
This form of the disease has already been described in a gen- 
eral way. It should be clearly distinguished from cases where 
Botrytis grows locally, more or less as a saprophyte, or even 
as a true parasite, upon the outer leaves. The rotting of the 
stem and collapse of the leaves and head is the character- 
istic of this and all types of the real “drop.” Botrytis vulgaris 
is well known as one of the fungi, though not, perhaps, the most 
common, which cause the death of young seedlings and cut- 
tings by what is known as “damping off,” a trouble entirely 
similar to the ‘‘drop” in its effect, being a rotting of the stem at 
the surface of the ground. The principal difference between 
‘‘damping off” and “drop” from a practical standpoint. is in the 
age of the plants affected. ‘ Damping off” of lettuce seedlings 'S 
common and may often be traced to Botrytis. It would not 
