62 
Make a DRAWING of the tissue as seen in this mount, showing the my- 
celium and the extent of its penetration. : : 
The hyphae invade the cell, using up the contents, and permit the air 
to enter the tissue, thus giving the white appearance to the center of the 
lesion. These hyphal threads grow upward and produce a stroma just 
below the cuticle; the cuticle is then ruptured permitting the fruit-stalks 
to emerge. : 
With the aid of pith, cut thin sections through the diseased area of the 
leaf. Mount these in water (or use prepared slides) and OBSERVE :— 
8. The location of the mycelium and its relation to the diseased 
cells. 
9. The mat of mycelium or stroma just below the cuticle. ; 
10. The three or more short stalks or conidiophores which arise 
from each stroma. Are they septate? A single conidium is borne on the 
tip of each conidiophore. The conidia will probably not be present in 
this mount. Why? : 
Make a DRAWING of a cross-section of a leaf showing the location and 
structure of the stromata with their conidiophores. ; 
For study of the conidia, scrape several of the spots on the leaf with 
the scalpel and’make mounts in potassium hydroxide. (If spores are not 
present, consult text books of Duggar, Stevens, or Tubeuf and Smith.) 
OBSERVE :-— 
11. Their size, shape and septation. DRAW. 
Saprogenesis. The infected leaves which drop to the ground 
are still farther invaded by the mycelium of the pathogene. This mycelium 
finally develops a sexual fruit-body or perithecitum. This is at first covered 
by the tissue of the leaf, but soon breaks through the epidermis. 
In the leaves provided OBSERVE :— 
12. Small black bodies just large enough to be seen with the 
naked eye, near or in the old lesions. They are never numerous. Make 
a DRAWING of part of a leaf showing these small black perithecia. Com- 
pare their size and appearance with the acervuli of Marssonia found on 
old fallen leaves of strawberry. (The two fungi are not related.) How 
can the perithecium be distinguished from the acervulus? 
With the aid of pith, cut thin cross-sections of a leaf containing perithe- 
cia (or use prepared slides). Under the microscope, OBSERVE :— 
13. That the perithecia are more or less hemispherical. 
14. That the wall of the perithecium seems to be made of two 
layers, the outer one being made up of thick-walled pseudoparenchymatous 
cells, and the inner one of thin-walled cells. 
15. That there is an opening at the tip of each perithecium,—the 
ostiolum. 
16. That arising from the inner base of the perithecium are 
club-shaped bodies,—the asci containing eight hyaline, uniseptate spores 
with acute ends. 
Make a pRawING of a cross-section of the perithecium, with the sur- 
rounding host-tissue. Make an enlarged pRAWING of a single ascus with 
its spores. 
It is from these spores that the primary cycles start, the following spring. 
The mycelium may also live during the winter in the partially green leaves 
and produce conidia the following spring, thus initiating primary cycles. 
