72 H. E. EWING. 



except that the selection should continue for increasing the body 

 length, or stature. The reason for doing this was to study the 

 effects of temperature and food upon the character under con- 

 sideration, especially to see if changing environmental conditions 

 should stimulate any germplasm change. In all 44 generations 

 were obtained. The first score of generations were treated in a 

 definite way, the conditions were considerably changed for the 

 second score of generations, and again changed for the last four 

 generations. 



First Score of Generations; Temperature not Regulated; Groivth and 

 Reproduction Period for Each Generation Not Made Uniform. 



For the first score of generations the aphids were reared on 

 young wheat shoots, in large glass vials which were used as 

 breeding cells. They were placed on these young wheat shoots 

 before the same were more than two or three days old. Usually 

 these wheat shoots were less than twenty-four hours old when the 

 lice were placed on them. Each louse was placed on the tender 

 white sheath of the shoot just above the soil. It was sometimes 

 found that after the shoots became a little older and had put 

 out their first leaf that the plant louse would migrate upward and 

 get on this leaf. When such a thing occurred the aphid was 

 always removed to the sheath of the shoot down next to the soil. 

 The breeding cells containing the young wheat shoots and plant 

 lice were kept in the laboratory under such conditions as were 

 found to prevail there. There was a great variation in temper- 

 ature and a considerable variation in humidity, but Headlee has 

 shown 1 that the latter does not affect the metabolism of aphids 

 when the variations are not greater than would ordinarily occur 

 under laboratory conditions. Further, no definite time was 

 allowed during the first 20 generations for the growth and 

 reproduction period of each fraternity. Individuals were allowed 

 to reach maturity and produce from several to as many as two 

 dozen offspring; then the parent individuals were killed, and 

 measured and selection was made. 



Selections in the first score of generations of isolation 1 1 were 



1 Headlee, T. J., 1914. "Some Data on the Effect of Temperature and Moisture 

 on the Rate of Insect Metabolism," Jour, Econom. Ent., Vol. VII., pp. 413-417. 



