44 INSECTS 



culture medium for a soot fungus which forms a black 

 covering -that disfigures if it does not kill the foliage or 

 fruit. It goes without saying that what is true of the 

 apple, which I have chosen for an illustration, is equally 

 true of the cherry, the maple, the orange, lemon or any 

 other tree or plant subject to the attacks of plant lice or 

 others of their allies also producing honey-dew mealy 

 bugs, white-fly, Psyllids and even some scales. 



FIG. 13. The apple louse: b, stem-mother; a, winged parthenogenetic form; 

 c, adult male; d, winter eggs on twig. 



To return, however, to our stem-mother on the 

 apple, whom we left engaged in the task of increasing 

 her kind. She was born without wings and never 

 acquires them, and her daughters are like her in this 

 respect. But after the second generation matters 

 become crowded, and unless relief is somehow obtained 

 there will be more than can be maintained on the orig- 

 inal tree. And so in the third and later generations a 



