96 H. E. EWING. 



this regard we must remember that the Iowa strain with which 

 this long-pedigreed Oregon strain was compared may have 

 differed from the latter genetically. Our conclusions can not 

 be final in regard to this point. 



THE OPTIMUM TEMPERATURE FOR THE PRODUCTION OF WINGLESS 

 AGAMIC FORMS, AND THE RELATION OF TEMPERATURE 



TO DIMORPHISM. 



During the early stages of the propagation of isolation u it 

 appeared best to determine with stock obtained from discards 

 of this subline the optimum temperature for the production of 

 wingless agamic forms, and to see if it was possible so to regulate 

 the temperature that only wingless forms would appear. Ex- 

 perience had shown that the growth of certain generations had 

 evidently been retarded by unusual temperatures, and to obtain 

 an optimum for growth would hasten the breeding very mate- 

 rially, and at the same time furnish more stable conditions for the 

 experiment. The appearance of occasional winged forms during 

 the first score of generations caused a complete loss, as far as 

 number of individuals used in the experiment was concerned, 

 as none of these was measured. If these winged individuals 

 could be prevented from appearing, and the line made com- 

 pletely monomorphic, a great gain would be accomplished. 



Accordingly mothers were placed in a constant temperature 

 cell, and the young were allowed to be born and reared at various 

 constant temperatures. The cell, which admitted light, was so 

 regulated by an electric thermo-regulator that it seldom varied 

 either way more than 0.2 F. The temperatures at which these 

 various individuals were born and reared were as follows: 60 F., 

 70 F., 80 F., and 90 F. At 60 F. all the individuals reared 

 produced winged forms. At 70 F. only 15.1 per cent, were 

 winged; at 80 F., 69.6 per cent, were winged, and at 90 F. no 

 individual lived to reach the last nymphal stage. 



From these results I judged that at 65 F., or slightly above 

 that, probably only wingless forms would be produced; certainly 

 only very few winged forms should appear. These predictions 

 were correct, for in the next 20 generations I so regulated the 

 temperature for isolation 1 1 that not a single winged individual 



