DAMPING-OFF IN FOREST NURSERIES. 6 
authors the most serious enemy encountered in growing softwood 
cuttings in Germany, if distinct would be a further addition to these 
generalized parasites. However, it is now believed (34) to be identi- 
cal with Corticium vagum. Common generalized parasites of older 
plants, such as Sclerotinia libertiana, Sclerotium rolfsii (129), and 
Thiela/via basicola (47), capable of attacking roots or other parts of 
older plants of numerous species, may also be considered among the 
damping-off fungi when they cause the death of small seedlings, as 
occurs, for example, in attacks by Sclerotinia libertiana on lettuce 
(20, p. 28) and celery (103, p. 536) in seed beds. Further study will 
probably result in multiplying almost indefinitely the number of 
more or less important damping-off parasites, both of the specialized 
and unspecialized groups, although the most important of the latter 
type are probably already known. 
Most of the references in literature to damping-off describe its 
occurrence in truck crops and the losses caused in these crops. Ac- 
cording to Haisted (53, p. 342), weed seedlings are also very com- 
monly attacked. Duggar (33) names lettuce, celery, cotton, sugar 
beet, cress, cucumber, and sunflower as especially susceptible to 
injury by the two most important damping-off organisms. Except 
for the plant species in which damping-off by seed-carried parasites 
is common, it appears that the economic damage from damping-off 
is serious only with plants whose culture involves the raising of the 
seedlings in crowded seed beds for subsequent transplanting. For 
example, tomatoes do not ordinarily suffer from damping-off in the 
field (70), but the growing of seedlings in flats for subsequent trans- 
planting is sometimes seriously hampered as a result of the preva- 
lence of damping-off. This same principle holds in general for trees. 
Broad-leaved trees, which are usually not as crowded in the seedling 
stage as are the conifers, seldom give rise to complaint on the score 
of damping-off. The conifers, subject to serious losses in nursery 
beds, are not believed to be greatly affected in this country by the 
better known t}^pes of damping-off under forest conditions (68) 
except in the less common cases in which seedlings come up in close 
groups from squirrel hoards, artificial seed spots, or similar sources. 
A considerable number of broad-leaved trees have been reported at 
one time or another as injured by damping-off, though complaints 
of commercially serious losses are not common. The cases which 
have come to the writer's attention are listed below : 
Cause not determined : 
Orange (43, 108). 
Olive, in greenhouse at the University of California. 
Russian wild olive (Elaeagnus sp.), serious at an Iowa nursery; oral re- 
port by Mr. C. R. Bechtle, formerly of the United States Forest Service ; 
at another nursery in the same region this plant was reported as very 
little subject to injury. 
