ROSE LOUSE. 
333 
remaining a considerable time, greatly disfigures 
the leaves, and is sometimes mistaken for a black 
mildew. 
In some seasons these insects multiply so ex- 
ceedingly as to become very injurious to the hus- 
bandman, who has no remedy against their baneful 
effects. Hop gardens are sometimes covered with 
them ; and the plants which before might be in 
the most flourishing state, are presently so altered 
in their appearance as to be no longer like the 
same. Vain would be the attempt to rescue them ; 
the mischief is too extensive : the timely fall of 
violent rain attended with lightning is said to be 
very serviceable in clearing the crop, but it may be 
doubted if the wet has much to do with it, since 
we find from some experiments made by Mr. Cur- 
tis, that these insects can even exist for a considera- 
ble time totally under water. On the twelfth of 
May 1 799, this gentleman immersed in a glass of 
water the footstalk of a leaf of considerable length, 
taken from a stove plant beset with aphides of a 
dark lead colour, which were feeding on it in great 
numbers. On immersion they did not quit the 
stalk, but immediately their bodies assumed a kind 
of luminous appearance from the minute bubbles 
of air which issued from them. They were put 
under water at a quarter past six in the evening, 
and taken out at a quarter past ten the next morn- 
ing, having continued immersed sixteen hours. On 
placing them in the sunshine, some of them almost 
immediately showed signs of life, and three out of 
