INSECTS. 313 



mur proved that one indrvidual, in five generations, may 

 become the progenitor of nearly six thousand millions of 

 descendants. Most of these insects, which we find so 

 abundant upon our trees, are wingless females. Winged 

 insects, both male and female, appear later in the season, 

 and after lay-ing their eggs, they soon perish. Some lay in 

 the fall, others wait till spring. When these eggs hatch, 

 the brood consists wholly of females, which are wingless, 

 and do not lay eggs, but are viviparous and produce from 

 fifteen to twenty young lice in the course of a day. This 

 second generation are also wingless, and at maturity pro- 

 duce their young, and so on to the seventh generation, 

 without the approach of a single male, until the autumn, 

 when a brood of males and females appears, which are 

 both winged at maturity, and then the eggs are laid for 

 the next year's brood, and the parents die.* 



The injuries occasioned by plant-lice, are much greater 

 than would at first be expected, from an observation of 

 the small size and extreme weakness of the insects ; but 

 these make up by their numbers what they lack in strength 

 individually, and thus become formidable enemies to veg- 

 etation. By their punctures and the quantity of sap they 

 draw from the leaves, the functions of these important 

 organs are deranged, or interrupted, the sap is withdrawn 

 or contaminated, and unfitted to supply the wants of veg- 

 etation. Plants are diflferently affected ; some wither and 

 cease to grow, th.eir leaves and stems become sickly, and 

 die from exhaustion. Others, not killed, are greatly im- 

 peded in their growth ; the tender parts, which are attack- 

 ed, become stunted and curled. The punctures of the 



• Harris, p. 205. 



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