S10 INSECTS INJURIOUS TO VEGETATION. 



chief nutriment both of the ants and their young, which is 

 sufficient to account for their solicitude and care for their valu- 

 able herds. 



The peach-tree suffers very much from the attacks of plant- 

 lice, which live under the leaves, causing them by their punc- 

 tures to become thickened, to curl or form hollows beneath, 

 and corresponding crispy and reddish swellings above, and 

 finally to perish and drop off prematurely. Whether our 

 insect is the same as the European Aphis of the peach-tree 

 {Aphis^ Persicce of Sulzer) I cannot determine, for the want of 

 a proper description of the latter. 



The injuries occasioned by plant-lice are much greater than 

 would at first be expected from the small size and extreme 

 weakness of the insects ; but these make up by their numbers 

 what they want in strength individually, and thus become 

 formidable enemies to vegetation. By their punctures, and 

 the quantity of sap which they draw from the leaves, the 

 functions of these important organs are deranged or inter- 

 rupted, the food of the plant, which is there elaborated to 

 nourish the stem and mature the fruit, is withdrawn, before it 

 can reach its proper destination, or is contaminated and left in 

 a state unfitted to supply the wants of vegetation. Plants 

 are difl'erently affected by these insects. Some wither and 

 cease to grow, their leaves and stems put on a sickly appear- 

 ance, and soon die from exhaustion. Others, though not 

 killed, are greatly impeded in their growth, and their tender 

 parts, which are attacked, become stunted, curled, or warped. 

 The punctures of these lice seem to poison some plants, and 

 affect others in a most singular manner, producing warts or 

 swellings, which are sometimes soHd and sometimes hollow, 

 and contain in their interior a swarm of lice, the descendants 

 of a single individual, whose punctures were the original cause 

 of the tumor. I have seen reddish tumors of this kind, as big 

 as a pigeon's cg^^ growing upon leaves, to which they were 

 attached by a slender neck, and containing thousands of small 

 lice in their interior. Naturalists call these tumors galls, be- 

 cause they seem to be formed in the same way as the oak-galls 

 which are used in the making of ink. The lice which inhabit 



