H. C. Experiment Station 
9 
organism attacks alfalfa and vetch. It seems desirable, therefore, that a 
comparative study of Sclerotinia trifoliorum and S. libertiana be made 
to establish their relationship to each other. They were accordingly 
isolated from crimson clover and from lettuce respectively and main¬ 
tained in culture under observation for a considerable period. 
The mycelium or vegetative body of the clover stem rot fungus appears 
under no conditions, except in the formation of sclerotia, to produce an 
abundant aerial growth on the surface of stems. It is then not loose and 
cottony, as in the case of lettuce drop fungus, in which there is a profuse 
mycelium, especially under conditions of high relative humidity. This is 
in accord with observations by Gilbert and Meyer (10) on Sclerotinia 
trifoliorum and Stevens and Hall (24) on Sclerotinia libertiana. Fur¬ 
thermore, constant differences in mycelial development are apparent in 
culture. On steamed cornmeal or potato agar, media noted to favor 
rapid growth of both organisms, S. libertiana makes the more luxuriant, 
rapid growth, a difference which persists even after sclerotial formation 
has been completed. Even though there is considerable variation in 
diameter of the hyphae, with an overlapping of extremes, the lettuce 
drop fungus possesses the larger, coarser mycelial threads. Compara¬ 
tive measurements of the younger growing tips, as shown in Plate 1, 
Fig. 1, indicate that the relative diameters are approximately in the 
proportion of 2 to 3. 
It does not appear to he possible to differentiate between the peculiar 
processes termed attachments, which have been described in previous 
accounts and which develop when contact between hyphal tips and wall 
of the culture flasks or Petri dishes is effected. In the case of each 
organism, the hyphae become flattened, septate, profusely branched and 
interlaced resulting in the formation of dark masses which adhere to the 
glass surfaces. 
The sclerotia of both are variable in shape, in that they are spherical, 
cylindrical, flattened or irregular, and in size which ranges in the case 
of S. trifoliorum from .3 to 10 mm. and to as large as 20 mm. in S. liber¬ 
tiana. In general, the latter is considerably larger as indicated in Plate 
2, Fig. 2. 1STo differences in development or structure were noted, how¬ 
ever. From 2 to 3 weeks are required for their formation. They begin 
as dense, floccose, white mycelial masses. After a few days the masses 
have increased in size, become compact and of a cartilaginous consis¬ 
tency. At this stage they are white to pale cream-colored, which color 
persists within although the exterior rapidly changes to an inky black. 
In culture on flasks of steamed corn meal, very abundant sclerotial for¬ 
mation results, forming in some instances, a sclerotial crust over the 
entire surface in the case of the clover stem rot organism, whereas the 
sclerotia remain for the most part separated in S. libertiana. 
