102 . DISEASES OF GLASSHOUSE PLANTS 
ment of C. fulvum, laboratory experiments having shown 
that the rate of growth is much slower in well-lighted 
conditions than in the dark. The minimum growth 
temperature is approximately 9° C., the maximum 
temperature 30° C., while the most favourable tempera- 
ture lies between 20° C. and 25° C. The fungus also 
grows best when the atmosphere is rich in moisture. 
Such facts are confirmed by observations in commercial 
nurseries, where outbreaks have generally occurred after 
periods of dull, humid weather. Also, those parts of a 
house or block of houses where the heat and water vapour 
tend to accumulate are notable as places where the 
disease first appears and spreads most rapidly. Thus a 
block of houses without dividing partitions, if built on a 
severe slope, develops leaf mould first at the highest 
level, where the heat and moisture accumulate. This 
can be obviated by interposing dividing partitions at 
intervals through the block. The disease also appears 
first at any spot in a house where the air tends to be 
stagnant and moisture accumulates. Any departure 
from a uniform level of the soil surface by the formation 
of hollows and depressions provides sufficiently moist 
conditions for C. julvum to develop. 
The disease is best controlled by providing a dry 
atmosphere for the plants, efficient ventilation and 
circulation of the air being important factors in this 
respect. It is equally important to trim the plants so 
as to allow the air to circulate freely between the leaves. 
Spraying with liver of sulphur and lime sulphur have 
been recommended as a means of control, but under 
commercial conditions it is practically impossible to do. 
much good by spraying, for the dense foliage and height 
of the plants render a complete wetting of the plant 
surface an almost impossible process. 
Dusting with sulphur powders helps to keep the 
disease in check, but is by no means a cure for it. Under 
commercial conditions the most convenient method of 
checking the progress of “leaf mould” is to vaporize 
