THE APHIS VASTATOR ON OTHER PLANTS. 85 



better, being in a more uncultivated, and therefore a more 

 natural condition. The wild potatoe resists the invasion to 

 a much greater extent than the cultivated varieties, and 

 these solanaceous plants present the disease in precisely 

 the same character as the wild potatoe. 



(342.) In some cases, a small portion of the leaf dies ; 

 in others, the effect is evidenced on a greater portion, or in 

 the whole of the leaf. The larger leaves are generally 

 first attacked ; and when the plant is weakened, the insect 

 migrates to the smaller leaves, and thus successively kills 

 every portion of the plant : it then takes wing, and flies 

 away to commit its ravages elsewhere. 



(343.) Next to plants belonging to the order of the So- 

 lanese, those included in the order Cruciferse appear to 

 suffer most. Besides the turnip and the Swede, to which 

 I have given a distinct chapter, I have found it upon the 

 radish, the cabbage, the brocoli, the wild turnip, the mus- 

 tard, the horse-radish, and other cruciferous plants. 



(344.) The cabbage and brocoli, although they are in- 

 fected with the vastator, are generally attacked by another 

 Aphis to so much greater an extent, that the vastator is but 

 of comparatively little consequence. The two kinds are 

 frequently to be met with upon the same leaf, committing 

 their ravages in company. 



(345.) The large and vigorous leaf of the horse-radish 

 might be supposed to be secure from injury from so small 

 and seemingly insignificant an animal ; yet the largest of 

 its leaves will be totally destroyed by the insect's agency, 

 and the plant will sho*w a tendency to rot at the junction 

 of the stem with the root. In this plant the disease ap- 

 pears in its early stage as minute points of discoloration, 

 which are observable at the places where the creature 



