PEACH SCAB AND ITS CONTEOL. 17 



production of microsclerotia, and (3) the depth of growth below the surface of the 

 medium. The most conspicuous development above the surface of the substratum 

 occurred on beerwort and synthetic agars. A greater or less development of this type 

 and the production of abundant microsclerotia occurred on all the sugary media used. 

 Little of the elevated stromateoid gi'owth occiured upon starchy media, nor were 

 microsclerotia observed in such cultures. The subsurface development on the 

 starchy media, however, was very vigorous. On agar in water the fimgus developed 

 slowly until the colonies were about Ih cm. in diameter, though they were considera- 

 bly less dense than on the more nutritive substrata, and their development above the 

 surface of the slant was very limited. The variations in strains from different organs 

 of the host were very minor, being no gi'eater than have been observed in strains 

 isolated from the same organ. 



Prune gelatin slants. — The early development of the fungus parallels that on prune 

 agar. The subsurface growth, however, soon becomes considerably more rapid on 

 the gelatin cultures. While no marked liquefaction is apparent, there is some evi- 

 dence of the softening of the medium immediately adjacent to the advancing hyphse. 

 It is quite possible that liquefaction occius very gi-adually, the liquefied areas being 

 occupied by the fungus as rapidly as the medium becomes softened. The fully 

 developed colonies occupy the entire slanted sections and extend somewhat into the 

 medium below. 



Lima-bean agar shale cultures. — The fungus develops quite vigorously and typically 

 upon the siirface of the medium, and good gi'owth occurs to a depth of 1 to 2 mm. At 

 greater depths colonies develop at various points throughout the cultiu'e, but they 

 grow very sparsely and barely become visible macroscopically. 



Other media. — The same strains of the fungus used for the agar slant cultures were 

 grown comparatively, at the same time and under like conditions, upon the following 

 media: Prune decoction (2 per cent) in (1) tubes, (2) elder pith, (3) plaster-of-Paris 

 blocks, and (4) filter paper; peach fruit and leaf decoctions in filter paper; steamed 

 bean pods; sweet-clover stems; peach twigs; peach leaves; potato plugs; rice; 

 corn meal; and sterile raw potato plugs. The developments were not sufficiently 

 distinctive to justify detailed descriptions. In the prune decoction the fungus 

 developed abundantly at the siuface of the liquid and formed fairly vigorous colonies 

 along the walls of the tubes to the bottom. Good growth occurred on all the other 

 media, though the development on raw potato was quite sparse while the plugs were 

 fresh. Later, the growth was very good. The most striking featm-e of these cultures 

 was the conspicuous development of microsclerotia upon the peach twigs. The 

 differences among the strains were no more marked than in the agar slant cultiues. 



RELATIONS OP MOISTURE. ^ 



The cultural studies reported above showed that the fungus may 

 grow vigorously on or in a suitable nutrient solution or saturated 

 substratum. If the substratum was gradually dried, however, the 

 cell walls of the fungus thickened and became ohvaceous, and chlamy- 

 dospores were developed in great abundance. In this condition the 

 organism was found to be highly resistant to desiccation. This was 

 strikingly shown in the case of Lima-bean agar slant cultures, which 

 were made on December 8, 1911, and kept in the laboratory, where 

 they dried gradually and became v.ery hard and brittle. On April 

 15, 1915, mycehal fragments from one of these cultures were plated. 

 Good growth and sporulation resulted. 



48408°— Bull. 395—17 3 



