74 DISEASES OF GLASSHOUSE PLANTS 
and is responsible for considerable financial losses to the 
industry. In normal years it first appears about the 
middle of April and increases in intensity up to the second 
and third week in May, when it reaches its maximum. 
In normal summer temperatures the attacks die down 
during the second half of June, July, and August, but 
reappear at the end of September, when the plants die 
prematurely. 
Disease Symptoms.—Diseased plants are usually 
stunted, but not invariably so, while the internodes, 
especially the younger ones, are badly developed. When 
the conditions of temperature and light are most favour- 
able to the fungus, the disease symptoms appear quite 
suddenly and the plant wilts while the leaves are still 
green. ‘The plants may recover their turgidity at night, 
but wilt again as the morning advances. The leaves 
wither from the base of the plant upwards, adventitious 
roots emerge from the stem, and the plant dies. The 
process of death is much slower when the conditions are 
less favourable to the fungus: yellow blotches appear 
on individual leaflets on the lower leaves, and these 
leaflets either wilt and wither or wither without wilting. — 
Under conditions least favourable to the fungus the 
leaves do not wilt, but gradually desiccate from the base 
of the plant upwards. Finally death ensues. On cutting 
open the stem of a diseased plant the wood is seen to be 
discoloured practically to the top of the plant—the colour 
varying from light to dark brown. The discoloration of 
the stem may be followed to the root, and the place of 
entrance of the fungus into the plant may be distin- 
guished by the intense browning at that point. The 
disease-causing organisms hibernate in the soil or compost 
from season to season and infect the young roots as they 
develop. Entrance to the plant is assisted by wounds, 
but experiment has shown that such are not essential for 
infection, Verticillium having the power to invade roots 
absolutely free from wounds. The fungus destroys the 
cortex at the point of entrance, and, entering the wood, 
