INSECTS AND DISEASES AFFECTING PLANTS. 271 



Many species of plants are attacked by this insect at the 

 root. Asters, particularly, are much injured by it. In 

 fact, when in excess, there is hardly a species of plant 

 exempt from its attacks. We have often seen this Aphis 

 clustering by thousands on the roots of melons, cucum- 

 bers, and of beets, to the very points of the roots, a foot 

 below the surface. 



The Green Fly (or Green Aphis) is prevented, (for I 

 contend that it should never be seen, so that it need be 

 destroyed), by fumigating with tobacco smoke, not less 

 than twice each week. We do it in a manner much more 

 simple and agreeable to the operator than is often prac- 

 ticed. Two or three times each week during the entire 

 season at which our green-houses are filled with plants, 

 we use a small handful of shavings, on top of which we 

 place about half a pound of tobacco stems, previously 

 made damp. The shavings are lighted, and the fire be- 

 ing on the cement flooring, is left to take care of itself. 

 If the floor, however, is of wood, provision should be 

 made against danger from fire. We use this quantity of 

 tobacco to every five hundred square feet of glass; we 

 burn thus five or six tons of tobacco stems every season, 

 but we rarely see a green fly. We have occasionally seen 

 this insect increase to such an extent in its different con- 

 ditions, that fumigation was powerless to destroy it, or 

 rather it would have required it to be applied so strong, 

 to dislodge the vast number of the enemy, that the plants 

 would have been injured. The safer way to treat a des- 

 perate case of this kind is to brush the insect off by hand, 

 or with a soft brush; this is a slow process, but an effec- 

 tual one. This condition of the plants can only be the 

 result of utter neglect. The green fly sometimes injures 

 plants which stand too near together, so that the leaves 

 get matted so closely that the fumes of the tobacco can- 

 not penetrate. This is a condition, where recourse must 

 be had to brushing the insects from the leaves, and, if 



