10 
BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 
Fig. 3.— Longitudinal section of a lesion from 
an Elberta peach twig of the current year's 
growth, showing the early subcuticular de- 
velopment of the fungus and a very early 
stage of cork formation. Camera-lucid a 
drawing. (Magnified 310 times.) 
cork layers may be formed before the final rapid swelling of the fruit 
prior to its maturity. In such cases stresses are set up and cracks of 
varying sizes result. In many cases such openings are scarcely 
macroscopic, but on badly diseased fruits, where the spots have 
become confluent, the cracks may ex- 
tend across an entire side of the peach 
and reach inward to the pit. 
Twig lesions. — In the early stages 
of twig infection, slender, branching, 
hyaline 5 septate hyphse of the fungus 
are found penetrating the subcuticu- 
lar areas immediately exterior to the 
cellulose walls of the epidermal cells 
(fig. 3). As the fungus develops, its 
ramifications become more general, 
its individual cells thicken, the un- 
derlying epidermal cells of the twig 
die, and the diseased areas are effec- 
tively cut off from the sound cortical tissues below by layers of 
cork cells. These corky layers are formed by means of tangential 
divisions of the subepidermal cells. It is not unusual, however, for 
the first division to be transverse, the daughter cells dividing tangen- 
tially. The two or three actively 
concerned hypodermal layers are, 
in each case, rapidly converted 
into a fairly uniform barrier of 
thin corky cells of meager proto- 
plasmic content. As the lesions 
age and the epidermal cells be- 
come more and more disorganized. 
the outer layers of subepidermal 
cells die and turn brown. 
After the advent of the dormant 
period of the host, the fungus con- 
tinues to develop throughout the 
fall, mild periods of the winter, and 
the spring. The subcuticular hy- 
phae increase in diameter and in 
number until they form stromate- 
oid layers which may extend over 
the entire lesions. While these structures may consist merely of 
single layers of cells, they are usually thicker, often developing into 
pseudoparenchymatous masses, six or eight cells deep (fig. 4). 
With the vigorous subcuticular development of the fungus, the 
cuticle is often slightly raised and at times broken, while the remains 
Pl.t, 4.— Longitudinal section of a lesion from an 
Elberta peach twig of the preceding year's 
growth, showing the abundant subcuticular de- 
velopment of the fungus and the vigorous pro- 
duction of conidiophores in the spring following 
infection. The host cells, which were badly 
disorganized, are semidiagrammatically repre- 
sented. Camera-lucida drawing. (Magnified 310 
times.) 
