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Scrape some of the conidia from the scab-spot on an apple. Mount 
and study. Compare them with those found in the prepared slide. They 
are sometimes 1-septate. : 
Make prawincs to show the variations in size, form and septation of 
the conidia. 
Saprogenesis. The mycelium in the primary lesions on the leaves 
continues to produce conidia until the leaves fall. The fungus, which has 
up to that time lived practically on the surface, now sends new branches 
of the mycelium throughout the dead tissues of the leaf. From this 
mycelium are formed the globose perithecia. They are formed just 
beneath the epidermis of the lower or upper surface of the leaf, being 
most abundant near the surface facing upward as the leaf lies on the 
ground. Examine the old apple leaves provided and OBSERVE :— 
16. The evidence of the old scab-spots of the summer. 
17. With the hand-lens the pimple-like perithecia scattered over 
both surfaces of the leaf just beneath the epidermis. Note the color, size, 
distribution, relation to the old scab-spots, and relative abundance on 
two sides of the leaf. 
Make a prawinG of a portion of the leaf to show the perithecia as 
seen with the hand-lens. 
With the scalpel, cut from the leaf a small’square of tissue showing 
an abundance of the perithecia. Place between pieces of pith and with 
a razor make freehand sections through the perithecia. Mount and study. 
OBSERVE :— 
18. The shrunken dead condition of the host-tissue. 
19. The imbedded perithecia. 
20. The mycelium of the parasite throughout the tissues of the 
leaf; its form and character. 
21. The structure of the perithecium. (Best made out in the 
stained sections.) The walls, their relation to the host-tissues, form, size, 
mouth or ostiolium and asci, with ascospores. How many ascospores in 
an ascus? 
Make a DRAWING to show the structure and contents of the perithe- 
cium and its relation to the host-tissues. 
The perithecia begin to develop in the autumn but do not mature 
their ascospores until spring at the time when the apple leaves and blossoms 
are unfolding. 
Secondary Cycles are initiated by the conidia from the lesions on 
leaves and fruits on the tree. Aside from their conidial origin, the secondary 
cycles which are continuously initiated throughout the season, do not differ 
from the primary. 
22. Study the germinating conidia. DRAW. 
The fungus forms on the fruit a thick stroma-like growth from the 
upper surface of which arise the short conidiophores bearing the conidia. 
In order to study this structure and the relation of the parasite to the tissue 
of the fruit, make thin cross-sections through the scab-spots on the half- 
grown fruits. OBSERVE :— 
23. The thick stroma-like mass of the mycelium. Note its 
i Sl aati structure; thickest toward the center of the 
spot. 
24. The short conidiophores with conidia. Find conidiophores 
that show different stages in their formation and development. 
