94 DISEASES OF GLASSHOUSE PLANTS 
innumerable spores, and so constitute a constant danger 
as a source of infection. Spraying with a solution of 
liver of sulphur and flour paste is recommended as a 
means of control in severe cases. 
Colletotrichum Leaf Spot or Anthracnose.—In its 
commonest form this disease first attacks the leaves, and 
may appear at any time during the life of the plant. 
It has occasionally been observed during the propagating 
period, but generally it does not appear until March or 
April, when the plants are well established in the house 
and some fruits have been cut. The time at which the 
plants are attacked bears no relation to their age, but is 
determined by the presence of suitable sources of infec- 
tion. On the leaves the spots are washed into the 
hollows of the leaf surface by the process of overhead 
damping. The lesions commence as pale green water- 
soaked spots, barely distinguishable by the untrained 
eye, but quickly assume a characteristic appearance, 
becoming dry and reddish-brown in the centre with a 
yellowish water-soaked surrounding zone (Fig. 23). The 
lesions vary in shape from an almost circular spot in 
areas untouched by any large vein to irregular amceboid 
patches where they form over a vein. The spots fre- 
quently crack in the centre, and the desiccated tissue 
may not infrequently be beaten out by the daily overhead 
damping. The spots increase rapidly in size, become 
more circular and blotch-like, finally coalescing, and the 
leaf dies. At the final stage the leaves have a scorched 
appearance and are covered with spots. Microscopic 
examination shows the presence of numerous minute 
acervuli bearing spores and setz on the upper surface of 
the leaf. 
As the disease advances lesions develop on the leaf 
petioles and stems, showing as sunken, water-soaked areas 
at first, but rapidly becoming dry and powdery. At 
first they are usually linear in shape, but may spread 
round the stem, and under glasshouse conditions it is not 
