376 PERNS : 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- 

 fteris, 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, 



* Fwmcu/o foliorum, Fries. 



