90 DISEASES OF GLASSHOUSE PLANTS 
cracked, and generally exhibits a canker-like appearance 
(Fig. 20). Innumerable minute black pimples may be 
seen on the surface of the lesions. These are flask-like 
vessels called pycnidia, which contain many tiny spores, 
by means of which the disease is able to spread. 
During its most destructive years the disease was 
extremely virulent. Affected plants died quickly and 
infection spread with alarming rapidity. Diseased plants 
should be at once removed and burned, and of recent 
years a solution of ‘‘ Cheshunt Compound ”’ has proved 
useful in preventing the spread of the disease from plant 
to plant. Sterilization of the soil by means of steam has 
proved successful in eliminating the disease from infected 
nurseries. 
A similar disease of the cucumber and vegetable 
marrow has been reported in this country, and Massee 
demonstrated that the fungus from the tomato was able 
to infect these plants also. 
Botrytis Stem Rot.—This disease is common to many 
plants grown under glass, and is especially important in 
the case of the tomato. Under conditions of excessive 
humidity Botrytis sp. attacks badly pruned leaf bases of 
the tomato and, gaining strength by feeding on this half 
dead matter, works into the healthy stem tissues, de- 
stroying the cortex, vascular ring, and pith in turn, and 
by cutting off the water supply to that part of the plant 
above the point of attack causes it to wilt. 
The first signs of disease are the appearance of grey, 
sunken areas on the stem, generally round a ragged 
wound or half dead leaf base. The lesion slowly enlarges 
and may finally extend from six to twelve inches along 
the stem and girdling it (Fig. 21). Once the stem is 
attacked the plant can be saved, but only by cutting out 
all the browned tissue and rubbing the wound thus made 
with a moistened lump of liver of sulphur or a crystal of 
copper sulphate. 
The disease may be prevented by careful pruning, 
