PEACH SCAB AND ITS CONTBOL. 15 
collecting the spores in a platinum loop of water touched to the ends 
of sporulating hyphse. In cases where other measures were neces- 
sary, individual spores were isolated by a method which the writer 
(1915) has described elsewhere. By the use of this method all the 
cultures reported upon in this bulletin were isolated from single 
spores. 
The organism was also isolated from leaf and twig lesions by 
sterilizing the surfaces with mercuric chlorid in the usual fashion 
and plating fragments in agar preparations. This method, however, 
was rendered unsatisfactory (1) by the superficial nature and slow 
growth of the fungus and (2) by the prevalence of a species of 
Dematium which agrees morphologically with the description of 
Dematium puUulans De By. This organism grows very rapidly in 
culture and forms myriads of spores, from which it is very difficult 
to isolate the slow-growing Cladosporium. 
In connection with these isolations, observations were made to 
ascertain what organisms are commonly associated with scab lesions. 
Hundreds of plates were made from scrapings from scab infections 
on fruits, twigs, and leaves. The media most commonly used were 
agar in water, with prune decoction added, Lima-bean agar, and 
Thaxter's potato hard agar. Cladosporium carpophilum developed 
uniformly when the plates contained freshly produced normal spores, 
but it frequently failed to appear if the lesions had passed through 
adverse conditions, such as exposure to excessive heat or drought. 
The following organisms appeared frequently: Dematium sp., Hor- 
modendron sp., and two undetermined imperfect fungi, hereafter 
designated for convenience as undetermined fungi A and B. While 
these four organisms appeared frequently and abundantly, only 
the Dematium developed constantly. All occurred superficially, 
and all were readily isolated from apparently normal surfaces of 
fruits, twigs, and leaves, as well as from scab lesions. The Dematium 
and the Hormodendron were especially abundant on dead tissues. 
While there was little reason to suspect that any of these superficial 
fungi bore a causal relationship in the production of scab, they were 
all isolated in single-spore cultures and tested for pathogenicity. 
The results, which were uniformly negative, are discussed later. 
CULTURAL CHARACTERS. 
Strains of the fungus isolated from (a) fruit, (b) twig, and (c) leaf 
lesions, respectively, were grown comparatively in triplicate cultures 
on 31 media. No marked differences occurred in the behavior 
of strains from the different organs of the host, the variations being 
no greater than those observed in strains isolated from the same 
organ. The fungus grew well on this wide range of media, and 
