PEACH SCAB AND ITS CONTROL. 11 
of the dead epidermal cells are compressed inward in extreme cases 
until their identity is almost lost. In such cases the fungus often 
grows down between the epidermal cells, and occasionally hyphse 
penetrate the intercellular areas of the first subepidermal layer. 
After the protective corky layers are fully formed, no further 
pathological anatomical changes occur. As the bark forms and 
roughens with the second year's growth of the twigs, the cuticle of 
the diseased areas partially sloughs off; and, as the bark thickens 
with subsequent development, the lesions gradually lose their 
identity. 
Leaf lesions.- — In the early stages of leaf infection, the slender 
hyphse of the fungus are found between the cuticle and the cellulose 
walls of the epidermal cells of the lower (dorsal) surface. As the 
fungus develops, its ramifications become more abundant, and 
under favorable conditions conidiophores and conidia are produced. 
Its ultimate development, however, is much less vigorous than upon 
twigs or fruit, no pseudoparenchyma having been observed on the 
leaf lamina. The invasion appears to be merely subcuticular and 
the fungus is very inconspicuous, even in well-stained preparations. 
The chlorophyll usually disappears from the mesophyll cells imme- 
diately adjacent to the invaded areas, while in extreme cases this 
abnormality extends into the leaf lamina to such an extent that the 
areas above the lesions appear distinctly yellow or purplish when 
viewed from the upper (ventral) surface. 
When infection occurs upon the petioles or larger veins, corky 
layers similar to those described for fruit and twig lesions are formed. 
In such cases the development of the fungus is distinctly more vig- 
orous than on the leaf lamina, but much less so than on fruits and 
twigs. 
THE CAUSAL ORGANISM. 
TAXONOMY. 
Von Thiimen (1877), at Klosterneuberg, Austria, first described 
the peach-scab fungus, naming it Cladosporium carpopltilum. Two 
years later the same author (1879, p. 13) emended his original de- 
scription. Saccardo (1886, p. 353) gives Von Thumen's emended 
description in slightly abbreviated form. Arthur (1889, p. 7) reviews 
the references cited above and gives a translation of Von Thumen's 
emended description. Oudemans (1901, p, 388) describes as Fusi- 
cladium carpopMlum Oud. a fungus growing on fallen young peaches. 
He lists as a synonym Cladosporium carpophilum Thum., but neither 
gives Von Thiimen credit as authority for the specific name nor 
states reasons for transferring the fungus to the genus Fusicladium. 
Aderhold (1900, p. 541-549; 1901, p. 656-657), after extensive 
investigations, concluded that Fusicladium cerasi (Rbh.) Sacc. 
should be referred to the genus Cladosporium. On comparing this 
