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: Pathogenesis. The ascospores constitute the inoculum for the 
primary cycles. With the scalpel remove a few of the mature perithecia 
and crush in a drop of water or potassium hydroxide on a slide. Cover and 
OBSERVE :— 
11. The ascospores; their form; number in ascus, number of 
cells and color. DRAW. 
If living material is available, study the germinating ascospores. 
These ascospores mature and are discharged from the perithecia, usually 
during March. They are carried to the buds on the previous year’s growth 
and infect the twig. The development of the pathogene and the reaction 
of the host is slow. Slight swelling of the infected twig begin to show 
by autumn. It develops rapidly during the early days of the following 
spring and burst through the epidermis. On the exposed surface, the 
scattered conidial stromata develop on which conidiophores bearing conidia 
are matured in late spring or early summer. ‘These conidia are dissemi- 
nated and initiate secondary cycles. 
Study cross-sections through the conidial stromata and OBSERVE :— 
12. The structure of the stroma; relation to mycelium in host; 
size of cells; color. 
13. The erect conidiophores; septate or non-septate? 
14. The conidia; shape, size, color and number of cells; where 
and how attached to conidiophores? 
Make a DRAWING to show these structures. 
After the conidia are matured and disseminated, the velvety covering 
of conidiophores gradually disappears, giving place to the continuous 
black crust-like stroma of the sexual stage which has been developing, 
so that by autumn the knot shows the black carbonaceous character, 
distinctive of its second season, and the minute pimple-like perithecia 
(fruit-bodies of the sexual stage) developing on the surface. 
During the first warm days of the spring (two years after primary 
infection) ascospores are formed within the asci in these perithecia. 
Examine with the hand-lens, the surface of mature galls provided. 
OBSERVE :-— 
15. The minute black bodies crowded together over the surface; 
shape and size; adherent to each other or separate on the stroma? 
16. The apex of the perithecia often depressed; a minute 
opening at the center of each,—the ostiolum. 
Study prepared sections through mature galls showing longitudinal sec- 
tions of perithecia. MAKE OUT:— 
17. The relation of perithecia to each other and to the stroma; 
character of the stroma as compared with that of the conidial stage. 
18. The structure of the perithecial wall; ostiolum; relation 
of asci and paraphyses to the perithecial cavity. 
Crush in water one of the mature perithecia. OBSERVE:— 
19. The structure of the asci, ascospores and paraphyses. 
Make an enlarged pRawING of a longitudinal section of the perithecium 
and supporting stroma to show these structures in detail. . 
The ascospores mature in early spring and are shot, during rainy 
periods, from the asci out of the ostiolum. Caught by the breeze, they 
are carried to the trees and infection occurs in the swelling buds or develop- 
ing shoots. Thus in two full years is the primary life-cycle, starting with 
ascospores, completed in the production of another crop of ascospores. 
