PEACH SCAB AND ITS CONTBOL. 15 



collecting the spores in a platiniun 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 

 sterilizmg 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 

 Dematiiun 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 carpopTiilum 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 tripficate 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 weU on this wide range of media, and 



