APPLE DISEASES 107 
troduced parasites, especially those of such alarming habits as 
the gooseberry-mildew fungus and others. 
The radiating threads which compose the blotches are hyphe 
of the fungus Leptothyrium pomi. Likewise the black specks 
belong to this fungus; they are sclerotial bodies. It is unknown 
just how the causal fungus passes the winter. It has been 
suggested that it hibernates on the apple-twigs, presumably as 
specks or sclerotial bodies. In the late spring each sclerotial 
body undergoes certain developmental changes which result in 
a pycnidium. Conidia, developed within the pycnidia, serve 
to bring about the first infections in the summer. On the sur- 
face of the apple a conidium germinates in the presence of mois- 
ture with the result that a radiating growth of mycelium is 
initiated. Apparently inoculations do not occur prior to the 
month of July. The threads extend themselves superficially, 
or at most penetrating the cuticle but to a slight degree. As 
the hyphe grow, they branch uninterruptedly until there is a 
prostrate, soot-colored mat of fungus threads; these compose 
the blotches, whence the name sooty-blotch. The cells of the 
radiating hyphe become enlarged and function in propagation 
by breaking away and causing new infections. This probably 
composes the inoculum during midsummer; for at this season 
no fruiting structures and no spores are to be found. When 
the fungus develops the fly-speck stage, the sclerotial bodies may 
possibly break away from the skin of the apple and may sub- 
sequently be washed to new quarters, where secondary infections 
may occur. This point, however, needs confirmation. In all 
cases the fungus is highly favored by damp situations and it is 
most abundant in seasons of considerable late summer rainfall. 
Little difficulty is experienced in dry seasons; in some years 
sooty-blotch and fly-speck are practically unknown. 
Control. 
Fortunately the disease may be kept under control by the 
methods of treatment employed for other more serious diseases 
