APHIS. 
183 
regard to blights: the one that the insects which 
cause them are brought from a distance by easterly 
winds; the other that they attach themselves to 
none but plants already sickly. Neither of these 
opinions, as far as I have observed, is founded in 
fact. I am induced from the numerous observa- 
tions I have made on insects for a series of years, 
(in pursuing the cultivation of plants) to consider 
the Aphis as by far the most general cause of the 
disease's distinguished by the name of Blights. 
Other insects it is true, more especially the larvae 
of some of the Lepidoptera, as those of the Pha- 
Icence tortriceSy disfigure and do infinite mischief to 
plants by rolling and curling up the leaves; but 
these for the most part confine themselves to 
certain trees and plants. Their ravages are also 
of shorter duration, being confined to the growth 
of one brood, and they are also less fatal. It 
wmuld be no difficult matter for me to fill a volume 
with observations to which I have been an eye- 
witness of the injuries which plants sustain from 
insects; but that would be foreign to my present 
purpose, which is to shew that the Aphis is the 
grand cause of these diseases, and to place the 
modus operand! or manner in which they effect 
this business in its true light.” 
“We are fully aware that certain gregarious 
insects may at particular times rise up in the air, 
and if small and light, be impelled by any wind 
that may chance to blow at the time; and on this 
principle we account for that shower of Aphides 
described by Mr. White to have fallen at Sel borne. 
