172 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
August, but reappear at the end of September. Fusarium wilt 
occurs at the height of the season, usually in July and August. 
The term " Sleepy Disease " aptly describes the appearance of 
the diseased plants. They are usually stunted in habit, but not in- 
variably so, and the internodes are badly developed, especially near 
the top, where the leaves form a rosette. When conditions are 
most favourable to the fungus, the symptoms appear quite suddenly. 
The plants may be perfectly turgid and green with no signs of yellow- 
ing, when, without any warning, the leaves become limp and droop. 
During the night the plants may recover their turgidity, only to wilt 
again as the morning advances. The plants wither from the base 
upwards and finally die. On cutting open the stem of a diseased 
plant the wood is seen to be discoloured, the colour varying from 
light to dark brown. The discoloration of the stem may be traced 
to the root, and the point of entrance of the fungus into the plant may 
be distinguished by the intense browning at that point. The disease 
organisms hibernate in the soil or compost from season to season 
and infect the young roots as they develop. The fungus destroys 
the cortex at the point of entrance and, entering the wood, passes up 
into the stem. Here it is found solely in the woody parts. When 
the plant dies the fungus leaves the vessels and-, penetrating the 
cortex, forms at the base of the stem a white external growth. This 
is the active fruiting stage, and the spores are readily blown about, 
enabling a rapid spread of the fungus. 
Experiments at Cheshunt have shown that plants grown " hard " 
are more susceptible to the disease than the softer succulent types, and 
consequently varieties like Kondine Red show a strong susceptibility. 
Considerable attention has been paid to the temperature relations of 
Verticillium wilt, and it has been found that temperatures between 
6o° F. and 75 0 F., with an optimum of 70-73 0 F., are favourable to 
the rapid progress of the disease, which below 6o° F. and above 75 0 F. 
is exceedingly slow, while suitable shading counteracts the effect of 
low temperatures. It has been found that wilted plants recover 
when the average temperature is raised to 77 0 F. and they are 
shaded. Based on these results, a method of controlling Verticillium 
wilt, by enforcing suitable cultural conditions, has been devised and 
tested with promising results. 
As soon as the wilt appears and it is proved that Verticillium 
albo-atrum is the pathogen, the average temperature of the houses 
should be raised above 77 0 F. by suitably increasing the boiler heat, 
regulating the ventilation, and by closing down the houses from two 
to four hours in the middle of the day. A light dressing of white- 
wash on the glass makes the conditions still more favourable for the 
plants. As little water as possible should be given to the roots, as 
heavy watering merely aggravates the wilting, but a* light overhead 
damping helps the wilted plants to recover. The plants should be 
encouraged to make fresh roots above the original diseased ones, by 
placing fresh soil round the base of the plant. 
