PARTHENOGENETIC PURE LINE OF APHIS AVEN^ FAB. 97 



appeared. Temperature changes alone, therefore, are capable 

 of affecting dimorphism. Upon the tender shoots of wheat I 

 produced either winged or wingless forms at will. It was a sur- 

 prise to me to find that both extremes of temperature caused the 

 appearance of the winged forms, and suppressed apparently 

 the appearance of wingless forms. 



How did these different temperatures affect the growth period 

 of the wingless individuals? At 60 F., no wingless forms were 

 produced; at 70 F. the average period of growth was 6 days; 



TABLE XI. 



DATA SHOWING EFFECTS OF VARIOUS CONSTANT TEMPERATURES ON APHIS 



AVENGE FAB. 



at 80 F., 7 days; at 90 F., 12+ days. It appears from this 

 that the optimum temperature for the growth of wingless in- 

 dividuals is very nearly the same as the optimum temperature 

 for the production of the same kind of individuals. It may be 

 these two optima are the same. 



The results of these experiments with constant temperatures, 

 which gave additional data soon to be considered, are given in 

 tabular form in Table XI. 



THE EFFECT OF TEMPERATURE ON GROWTH, SIZE, REPRODUC- 

 TION, AND MORTALITY. 



While starting the constant temperature experiment primarily 

 to determine the optimum for the production of wingless agamic 

 forms, it appeared profitable to observe also the effects of dif- 

 ferent constant temperatures on growth, size, reproduction and 

 mortality. 



