296 MANUAL OF FRUIT DISEASES 
grown in higher places are more free from scab than those in 
low areas. 
The twigs have more or less circular blotches of a yellowish 
brown color, with a dark-gray or bluish border. Frequently 
the spots become confluent, masking the normal pink-brown 
color of the young bark. The cuticle is separated from the 
cells beneath, corky cells are developed under the lesion, 
and in some cases the cambium is killed, and as a result the 
twig dies. 
That portion of the leaves of the peach lying midway be- 
tween the main veins is especially affected. Brown, scattering 
spots are developed in which the tissue dries up and finally 
falls away, leaving circular holes. 
Cause. 
Peach-scab is caused by the fungus Cladosporium carpophilum. 
Its mycelium occupies the space left by the partial separation 
of the cuticle from the underlying cells. On the twigs the 
mycelium hibernates in the form of dark-brown spherical 
cells. It is possible that conidia lying about the lesions may 
also be capable of tiding the fungus over winter. From the 
resting-cells described above, conidia are produced in the 
spring, and the latter are carried to the leaves and fruits. Ger- 
mination follows shortly and penetration is effected. Inocu- 
lation begins four to five weeks after the petals fall, but symp- 
toms do not show to the naked eye for about three weeks subse- 
quently. Inoculations and infections continue to take place 
until about one month before the fruit matures. As the fungus 
grows on the fruit the mycelium attaches itself closely to the 
surface between the hairs, forming a mat of short, plump cells 
which give rise to conidiophores and conidia. The flesh of 
the peach is not penetrated, but the close contact of the fungus 
with the outer cells allows absorption of nutrition from the 
fruit through the unbroken walls. Evidently there is some 
injury to the outer cells, for a cork-layer is developed just 
