1895] Development of Uncinula. 487 
and during the months of September and October it may be 
ound in an active stage on leaves, fruit, tendrils, and growing 
shoots, covering the same with a whitish, powdery, meal-like 
growth, which has caused it to receive its characteristic name. 
The powdery appearance is due largely to the presence of the 
mycelium and conidia of the fungus, which develop as de- 
scribed below. 
Mycelium.—The mycelium consists of thin-walled, nearly 
hyaline, sparingly septate threads, which are very variable in 
thickness, but average from 6 to 7# in diameter. The 
threads usually run in all directions, but show a tendency to 
converge at certain points (fig. 1), crossing and recrossing 
each other until a more or less thickened mat is formed. Al- 
though the mycelium does not become noticeably abundant 
until July, it may be found much earlier by carefully search- 
ing vines known to be susceptible to the attacks of the fun- 
gus. It occurs on such vines soon after the leaves put out, 
forming more or less rounded patches, which are difficult to 
See without the aid of a hand lens. 
Haustoria.—At numerous points on the mycelial threads, 
More or less lobed swellings are formed (figs. 1 and 2). These 
are somewhat rounded on the upper side, but next to the leaf 
they are flat, clinging close to the surface. These swellings 
are the haustoria, and from their under side fine thread-like 
Projections grow out and into the epidermal cells of the host. 
Once within the cell the end of the haustorial filament swells 
into a bladder-like body (figs. 3 and 4), which is filled with 
granular matter like that in the mycelium 
Contdia.—At numerous points the mycelial filaments send 
These are 
