DISEASES DUE TO FUNGI 93 
ing an ochreous-brown colour. The spots are definite in 
outline, irregular in shape, and may be distinguished 
readily from other leaf spot diseases. Frequently the 
entire leaf withers within the space of forty-eight hours 
after infection. 
An examination with a pocket lens of the upper 
surface of a “spot ’”’ shows the presence of brown erect 
fungal filaments, bearing conidia at their tips. These 
conidia are comparatively large, cylindrical in shape, but 
narrowed towards one end, 
and each possesses seven to 
nine cross walls (Fig. 22). 
Infection spreads rapidly, the 
conidia being easily blown 
about the house, as well as 
being transported by the 
workers, insects, and by the 
process of overhead damping. 
The disease can only 
attain epidemic proportions 
under conditions of high 
temperature and humidity, 
but rapidly growing, sappy 
plants are more susceptible 
to attack than slow growing 
plants with harder tissues. It 
has been observed that the 
tops of badly diseased plants Fic. 22. Spores of Cercospora melonis. 
. grow away clean if by any chance they pass through the 
ventilators into the open air. Similarly, cucumbers grown 
under frames or in the open air are not attacked by this 
disease. 
The control of the disease depends very largely upon 
the humidity of the glasshouse atmosphere, and efficient 
ventilation readily checks it by drying out the moisture 
from the house. All diseased leaves should be at once 
removed and burnt, for if these fall upon the damp 
earth they become covered with a fungal growth bearing 
