118 
12. The dwarfing effect on the inflorescence. Flowering is 
often partially or entirely prevented. 7 ; 
Make a series of DRAWINGS to show the symptoms exhibited by mildewed 
phlox. 
On peas. Both sweet peas and garden- or field-peas are affected. 
Examine the material provided and NoTE:— 
13. That the mycelial coating spreads almost uniformly over 
the entire leaf-surface, stems and pods. 
14. That it is much thinner than that on rose or phlox, and is 
web-like instead of felty. 
15. That there is little difference in the character of the mycelial 
coating on the upper and lower surfaces of the leaf. 
16. The general effect on the growth of the plant. Is dwarfing 
marked? Peas are usually affected late after growth is largely completed. 
17. The minute black perithecia in groups here and there in the 
mycelial weft; not prominent; usually not found on sweet peas. 
Make prawincs to show the powdery mildew on peas. 
On lilacs. The powdery mildew on the lilac is so common as to be 
almost always found on lilacs wherever grown and every year. ‘The leaves 
are the organs affected. Examine the material provided and OBSERVE :— 
18. The character of the mycelial coating. On which surface of 
the leaf does it develop? 
19. The minute black perithecia; their arrangement and 
distribution on the leaf. 
20. Any evidences of pathological effects on the leaves. 
Make prawincs to show the symptoms of the mildew on lilac leaves. 
On bittersweet. This mildew is not only common on Celastrus scan- 
dens L. but affects the foliage of many shrubs and trees. Examine the 
leaves provided and oBSERVE :— 
21. The size and location of the spots; the habit which this parti- 
cular mildew-pathogene has, of sending mycelial branches into the leaf- 
tissues through the stomata, is responsible for the location of the spot. 
22. The chlorotic effect on the leaf-tissue beneath the mildewed 
area as evidenced through the upper surface. 
23. The character of the superficial mycelial growth. 
24. The comparatively large and numerous perithecia in all 
ig of development, the younger ones smaller and brown or yellow in 
color. 
DRAW to show a leaf with a mildewed spot. 
ETIOLOGY 
Powdery mildew pathogenes all belong to the Erysiphaceae, a family 
of ascomycetous fungi. They are characterized among other things by 
their habit of growing externally over the surface of their hosts. They 
attach themselves by means of short haustoria sent into the epidermal 
cells. One or two species are known to send intercellular hyphae through 
the stomata into the tissues. The diseases above studied and their 
respective pathogenes are:-—the powdery mildew, 
of rose, caused by Sphaerotheca pannosa (Wallroth) Léveillé; 
of phlox, caused by Erysiphe Cichoracearum DeCandolle; 
