177 
which results in these numerous asexual spores without a mycelial stage 
intervening, constitutes in reality asexual reproduction, and that these 
spores are conidia. This is largely theoretical, however, to account some- 
how for a conidial stage. 
DRAW a portion of the lower epidermis as seen in prepared cross-sections 
showing mycelium, holdfasts, and young and old asci with spores. 
Saprogenesis. The whereabouts and activities of this pathogene 
during saprogenesis, if such a period ensues, is unknown. 
Pathological Histology. Although the mycelium of T. coerulescens 
is confined to the space it makes for itself between the lower epidermal 
cells and the cuticle, the effect of the parasite is seen throughout the thick- 
ness of the leaf. In the stained cross-sections, find and compare the healthy 
with the diseased part of the leaf. NoTE:— 
10. The hypertrophy in the lower epidermis, spongy mesophyl, 
palisade-mesophyl and upper epidermis. 
11. The hyperplasia in the lower epidermis and spongy mesophyl- 
tissues. 
12. That in the normal tissue the cells of the lower epidermis 
are longer than broad. The effect of the fungus is to cause these cells to 
increase greatly in size and, being so tightly packed together, they elongate 
in a direction perpendicular to the surface of the leaf. Finally septa may 
be laid down at right angles to their long axes. 
13. That the cells of the spongy mesophyl are increased both 
in number and size and are tightly packed together, largely eliminating 
the intercellular spaces so common in the healthy tissue. 
14. That the cells of the palisade-mesophyl are longer and wider 
than the normal. 
15. That the cells of the upper epidermis are somewhat larger 
and more globose than the normal. 
16. That the chloroplastids in the diseased cells are much 
smaller and fewer in number. 
Make prawincs showing (comparatively) the histological structure 
of the diseased and normal portions of the oak leaf. Preserve correct 
proportions between the two drawings. 
REPORT 
1. From the literature on leaf-blister of oaks and the methods 
used for control of peach leaf-curl, suggest possible measures of control for 
leaf-blister. 
