slight convexity or malformation, the lower layers of cells in the 
leaves having continued to grow, while the development of the - 
cells near the upper surface was prevented by the action of the 
fungus. This mildew is also found on the lower surface of the 
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_ leaves, but never to the same extent as upon the upper side, and 
asitis only in the latter part of the season that it has been 
observed there at all, its presence is doubtless due to-an extension 
of growth from other parts, as from the petiole. 
Upon the young and tender shoots the fungus is often particu- 
larly abundant, its action being to check their growth. Its pres- 
ence on the older and half-ripened shoots is indicated by distinct 
but irregular brownish blotches in the epidermis. Sometimes the 
Unecinula appears during the season of bloom, and, coming on the 
newly expanded flower, causes them to abort. Attacking very 
_ young berries, when these are no larger than shot or small peas, 
their growth is permanently checked. Cases have come under my 
observation where the Pernospora, the Uncinula, and the fungus 
of the black rot were all engaged in their work of destruction upon 
a single bunch of grapes. It is needless to say that the destruc- 
tion was complete. Upon the older berries the presence of the 
powdery mildew is made evident, before the mycelial threads have 
obtained sufficient growth to become conspicuous themselves, by 
the minute brownish spots produced by the action of the suckers 
on the epidermal cells. These spots eventually become confluent, 
the epidermis dies or is so affected that it will no longer expand 
with the growth of the berry, and consequently bursts, first form- 
ing tiny then gaping tears, the result being the death and decay of 
the berry. Oftentimes the fungus spreads over only a small 
portion of the berry; this part ceases to grow and a much dis- 
torted or imperfectly formed fruit is the result. The distortions 
are often carried so far that the berries crack open, exposing the 
seeds. We sometimes find nearly full-grown berries completely 
overgrown with the mycelium of the Uncinula, so that the brown 
specks above mentioned, if present at all, are completely hid from 
view. These berries eventually become. dry and shriveled, and 
finally drop off. 
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2 ix 
