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 growth occurred 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 fungus developed 
slowly until the colonies were about lh 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 greater 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 hyphae. 
It is quite possible that liquefaction occurs very gradually, 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 shake cultures. — The fungus develops quite vigorously and typically 
upon the surface of the medium, and good growth occurs to a depth of 1 to 2 mm. At 
greater depths colonies develop at various points throughout the culture, 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 surface 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 feature 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 cultures. 
RELATIONS OF 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 olivaceous, 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 very hard and brittle. On April 
15, 1915, mycelial fragments from one of these cultures were plated. 
Good growth and sporulation resulted. 
48408°— Bull. 395—17 3 
