200 



FUNGOUS DISEASES OF PLANTS 



affected with this sclerotial disease. From a series of experi- 

 ments extending through several years, Smith was unable by 

 any means to produce a conidial stage from cultures of the 

 Sclerotinia Libertiana sclerotia, and he believes, moreover, that 

 there exists another type of this fungus in which no conidia are 

 produced and in which the more minute sclerotia are incapable 

 of producing the apothecia. Whether or not there is any connec- 

 tion between the large sclerotinial type, which must be designated 

 as Sclerotinia Libertiana, and the smaller type above referred to, 

 it is unquestionably true that there exists a disease of lettuce and 

 other greenhouse plants of which the small sclerotium-producing 



FIG. 76. THE LETTUCE DROP : CONTROL (HEALTHY) AND INOCULATED 

 (DISEASED) PLANTS 



fungus is the cause. The writer has found this type of the fungus 

 to be the cause of an important disease of- lettuce in New York 

 and Boston, and inoculation experiments have invariably shown 

 the disease to be unusually virulent (Fig. 76). Sclerotinia Liber- 

 tiana has been several times reported as an important disease of 

 the cucumber, and according to Humphrey it is rather common 

 in the cucumber houses in Massachusetts. Humphrey supposed, 

 however, that the Botrytis which he found upon diseased plants 

 was connected with the sclerotial stage, but no sufficient proof of 

 such connection is afforded by the work which he reports. 



The sclerotia of this species are said to reach 3 cm. in length 

 in exceptional cases. The asci .are cylindrical, and measure 1 30- 

 135 X 8-io/u, while the spores are small, 9-13 X 4-6.5 ^. 



