376 
FERNS : BRITISH AND FOREIGN. 
abode, by the appliance of boiling-water, sulphur 
fumes, or exploding gunpowder : when such agents 
can be used, they deal with them quickly and whole- 
sale. Various kinds of traps are used, which, with 
poison, will, if daily attended to, completely extirpate 
them. But it must be borne in mind that, although the 
whole, old and young, may be got rid of in the course 
of a fortnight by poison — the effect of which is 
greatly increased by the living eating the poisoned 
dead, — eggs are however left, which will soon pro- 
duce a new generation that must not be allowed to 
arrive at maturity. 
Under the ordinary varying atmosphere of hot- 
houses, insects seem not to be affected, for if their 
extirpation is not attended to, they will be found in 
more or less abundance all the year. Not so the 
sooty mildew,* a fungus covering the upper surface 
of the leaves of plants with a black, sooty coat, and 
for their sudden appearance, like that of the grape 
mildew, the potato disease, and other sporadic 
plagues, no satisfactory causes have as yet been 
assigned. The pest now under consideration may be 
called one of these plagues ; in some years it is not 
seen, while in another it soon overruns and quickly 
covers Ferns, and other plants, in hothouses. The 
broad-fronded species of Aspidium, Meniscium, Gonio- 
pteris, Angiopteris, &c., are very subject to its attacks. 
Books on mycology name and describe these pests,, 
but not how to prevent them ; and books on horti- 
culture instruct how to get rid of them ; the principle 
of which seems to be dusting with sulphur, washing. 
Fumago foliorum, Fries. 
