1¢00 | BOTRYTIS AND SCLEROTINIA 387 
originally from lettuce in a house which had never contained 
any other form of the disease. In this culture the usual small 
sclerotia were first produced, but later there appeared a con- 
siderable number of larger ones, appearing similar to those of 
S. Libertiana. A number of these were obtained and cultures 
made from them on ordinary prune bread, with the result that 
the typical large-sclerotia type developed. No spores of this 
type had ever been developed in the laboratory at the time this 
culture was made nor had any trace of the large-sclerotia form 
ever appeared in connection with any of the material used, so 
that there would seem to have been no possible chance for acci- 
dental infection. Consequently the only possible explanation 
seems to be that Sclerotinia Libertiana developed directly from the 
small-sclerotia, no-botrytis form.3 (In this connection should be 
borne in mind the fact already mentioned that in one case one 
of the small sclerotia started to develop an apothecium just as in 
os Libertiana. ) 
CONCLUSIONS. 
From all the observations and experiments thus far recorded 
it is concluded : 
I. That the lettuce “drop” in Massachusetts is caused by 
two distinct species of fungi, namely, Botrytis vulgaris Fr. 
and Sclerotinia Libertiana Fckl., which are remarkably alike in 
Some respects and have an entirely similar effect upon the 
plant. 
2. That the bulk of the disease is caused by a degenerate 
form of the latter species, which has almost entirely lost the 
ability to reproduce by spores but which is highly specialized as 
4 vegetative, facultative parasite. i 
3. That the disease is caused by Botrytis vulgaris and the typi- 
Cal Sclerotinia Libertiana in mature plants only in rare instances; 
the former on account of its inability to attack vigorous plants 
under normal conditions, the latter because of its infrequent 
°Ccurrence, 
3It is not asserted that this result is to be attributed to the alkalinity of the cul- 
ture medium 
