ENpDOTHIA CANKER OF CHESTNUT 577 
looser (Fig. 92, e) and those branches that extend into this loose central 
area begin to cut off regular cells (pycnospores) from their apices. More 
branches (conidiophores) now grow in and cut off spores from their apices, 
until the wall, which constantly recedes as the pycnidium becomes larger, 
is completely lined with the brush-like hymenium (Fig. 86, page 559) 
and the cavity is packed with spores. Meanwhile an ostiole is formed 
by the loosening of the hyphz at the apex, and the spores are forced out 
through it in a gelatinous mass. The cells of the loose wall seem never 
to divide meristematically, and the wall in this type never appears 
pseudoparenchymatous. 
The first outward indication of the formation of pycnidia on the young 
canker is the appearance of numerous small, raised, smooth blisters just 
back of the advancing edge of the lesion (Plate XXXVIII, Fig. 1). 
They show no relation to the lenticels. Under each blister is the beginning 
of asingle pycnidium. At this stage the pycnidia are more or less globose 
cushions with a moist, gelatinous appearance; about half of the pycnidium 
is imbedded in the disintegrating collenchyma tissue, the other half pro- 
jects upward and raises the cork layer to form the pimple. There is no 
stroma at this time, but each pycnidium is early surrounded with a fringe 
of loose mycelium which is the forerunner of a stroma. A cross section 
of this hygrophanous cushion shows it to be a closely wound ball of hyphz 
corresponding to the stage represented in Fig. 92, c and d. It increases 
in size and develops into a mature pycnidium just as the process on agar 
was described above, pushing up the cork layer and finally causing it to 
rupture at the tip, from which point the spores are forced out. Mean- 
while the stroma is forming about the pycnidium. So far as observed, 
the stroma never precedes, but always follows, the early stages in the 
development of the pycnidium. With the active increase in the amount 
of stromatic tissue which is constantly added from below, the pycnidia are 
pushed out in the top of the stroma through the cork layer. Meanwhile 
they continue to increase in size and become irregular in shape. (Fig. 84, 
page 558, and Plate XL, Fig. 1). Often the entire stroma is found 
honeycombed with numerous communicating lobulated chambers. 
Time of production of pycnospores.— In Pennsylvania during the seasons 
of 1912 and 1913 the spore horns first began to appear on the cankers 
about the middle of April; after that they could be found at any time 
during the summer, being especially abundant after periods of rain. 
During the season of 1912, on cankers produced by inoculation in the 
spring, the tendrils were abundant after each rain period until the latter 
part of the summer, when the perithecial stage began to develop; after 
that, few spore horns were found on the cankers. Heald and Gardner 
(1913 a) state that pycnospores are produced in enormous numbers during 
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