THE LEAF LOUSE. 15? 



General colour Viviparous. 



These lice, or aphides, are usually found upon 

 the leaves of the orache, and other plants; and 

 the weaker the leaves and buds are,, these insects 

 swarm upon them in greater abundance. Some 

 plants are covered over with them; though they 

 are not the cause of the plant's weakness, but the 

 sign: however, by wounding and sucking the 

 leaf, they increase the disease. They generally 

 assume their colour from the plant on which they 

 reside. Those that feed upon pot-herbs and 

 plumb-trees, are of an ash-colour; only they are 

 greenish when they are young; those that belong 

 to the alder and cherry-tree, are black ; as are 

 also those upon beans, and some other plants: 

 those on the leaves of apples and rose-trees, are 

 white; but as they leap like grasshoppers, some 

 place them in the number of the flea kind. The 

 most uncommon colour is reddish; and lice of 

 this sort may be found on the leaves of tansey ; 

 and their juice, when rubbed in the hands, tinges 

 them with no disagreeable red. All these live 

 upon their respective plant; and are often en- 

 gendered within the very substance of the leaf. 



These are viviparous insects; the foetus, when 

 it is ready to be brought forth, entirely fills the 

 belly of the female; its fore-parts being excluded 

 first, and then the hinder. The young one does 

 not begin to move till the horns, or feelers, ap- 

 pear out of the body of the old one; and by the- 

 motion of these it first shows signs of life, moving 

 them in every direction, and bending all thej? 



