88 
18. The appearance of the ‘‘pimples’’,—the subcortical pycnidia. 
(See illustration photograph 8, and photographs 1-5.) = 
Make sections or study prepared slides of sections through the pycnidia. 
NOTE :— 
19. The mass of mycelium of the fungus aggregated in the outer 
bark just at the base of the fruiting structures. Such a ‘“‘bed” of mycelium 
is termed a stroma. (See illustration photograph 2c.) 
20. That this stromatic layer of mycelium encases the spore- 
bearing cavities. The fruit-bodies are said to be encased or enclosed in a 
stroma. 
21. The irregular convoluted cavities in the stroma,—the pycni- 
dia. (See illustration photograph 13c.) 
22. The compact laver of pycnospores lining the entire inner wall 
of the pycnidium (photograph 6). 
23. The manner of the cutting-off of the pycnospores (photo- 
graph 6). 
24. That each stroma contains a single pycnidium and that 
the spores produced are pushed out of the ostiolum through a rupture in 
the bark in the long thread noted above. These spores are disseminated 
and initiate secondary cycles. 
Make prawineGs to show these points. 
After a short period of pycnospore-production, the stroma grows to the 
extent that the bark is pushed back and a cushion-like structure is raised 
considerably above the surface. These stromata are at first reddish in 
color, but later at maturity of the spores they are a chocolate-brown and 
covered with numerous small projections or papillae. (See illustration 
photograph 11 and photographs 23, 30-33.) In the material provided, 
OBSERVE :-— 
25. The extent of the stroma as compared with that of the 
pycnidial stage. (See illustration photograph 13c.) 
26. The cavities here are simple flask-shaped perithecia. (See 
photograph 11 and illustration photograph 14.) 
27. The thick, lead-colored walls of the perithecia. 
28. The long black necks leading from the perithecial cavity 
to the surface of the stroma where they open through the papillae by the 
ostiola. (See illustration photograph 14.) 
29. The numerous asci contained in the perithecia and floating 
about (photographs 34-37). 
DRAW showing the perithecium in longisection. 
The ascospores produced on the canker are washed down the tree and 
can initiate secondary infections at any slight wound in the bark. Event- 
ually the tree becomes covered with cankers and dies. : 
Saprogenesis. The fungus does not require saprogenic conditions 
for the continuance of its cycles. On the other hand it is capable of exist- 
ing as a saprophyte producing both spore-stages, the perithecia following 
the pycnidia as in pathogenesis. Whenever a saprogenic habit is assumed, 
it is purely incidental and not a definite stage providing for something 
which cannot be produced during pathogenesis. Strictly speaking, 
however, the perithecial stage may, although produced abundantly on 
cankers on living trees, be considered as the saprogenic stage since it is 
developed far back from the advancing margin and probably is largely 
or entirely fed by saprophytic mycelium. 
