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9. That the leaves are narrow, have failed to expand and are 
curled and deformed. Chlorophyl is not developed properly and the leaves 
show red and yellow tints. Defoliation often results from a severe infec- 
tion. 
10. The effect on the more succulent upper parts of the twigs. 
11. The felty character of the superficial mycelium which forms 
in white patches over affected leaves and twigs. This thick mycelial 
felt persists on the twigs after the leaves fall, becoming a dirty gray-brown 
in color. 
12. The more or less circular white patches of mycelium on the 
fruit. When very young fruits are affected they soon fall. 
Perithecial fruit-bodies rarely appear. 
Make prawincs to show the symptoms exhibited by the powdery 
mildew of the peach. 
On the grape. This disease is more destructive and develops more 
typically in the Pacific Coast regions than in eastern United States. All 
herbaceous parts of the host are affected. Examine the specimens pro- 
vided. OBSERVE:— 
13. The whitish patches on the upper and lower surfaces of 
the leaf. How do they compare with the spots of the downy mildew? 
These spots may spread to form a whitish, mealy coating over the greater 
part of the leaf-surface. Badly diseased leaves may curl upwards about 
the edges. : 
14. The small black perithecia scattered over affected areas on 
the leaves. 
15. The diseased canes. They also show the superficial greyish 
white patches of mycelium beneath which the tissues of the cane soon 
darken, making it spotted. (See California Bul. 186, fig. 3.) 
16. The diseased berries. (See California Bul. 186, fig. 4.) 
Blossoms and young fruits when affected, quickly fall. The disease may 
often cause shelling of the large green berries when the fruit-pedicles are 
affected. 
Make prawincs from specimens and illustrations to show the symptoms 
of the powdery mildew of grapes. 
On the gooseberry. In case of the gooseberry mildew, it is chiefly the 
young shoots and the fruits that are affected. In the material provided, 
OBSERVE :— 
17. The mycelial mats coating the shoots; color, thickness 
and distribution. ; 
18. That the superficial mycelium spreads out over-the leaves. 
How is the growth of leaf and stem affected? 
19. The character of the mycelial patches on the fruits. Does 
the growth and development of the fruit appear to be affected? 
20. The black perithecia of the pathogene embedded in the 
mycelial felt. 
This same gooseberry mildew may sometimes seriously affect some 
varieties of currants, as may be seen in the specimens provided. 
Make prawincs of mildewed shoots and fruits of gooseberry or currant. 
_On the chestnut. The leaves are the organs affected. This powdery 
mildew affects not only chestnut but a great variety of trees, shrubs and 
woody vines. Examine the diseased leaves provided. oBSERVE:— 
