422 



a day longer when the temperature remained the same or when, if dif- 

 ferent, it was reduced to the same velocity value. Heavy rainfall lengthens 

 time in the apple (Fig. 28). Little or no rainfall shortens it. 



(3.) Air Movement and Evaporation. 



A large series of larvae were subject to various rates of evaporation 

 measured by the porous cup atmometer. Mortality was high, and com- 

 plete losses in certain evaporation rates rendered some sets useless. The 

 excellent success attending the use of the porous cup atmometer with 

 plant work has not attended our efforts. The reason for this is that 

 higher temperature, which accelerates development, increases evaporation ; 

 while increased rainfall and humidity, which accelerate development, de- 

 crease evaporation. Although high mortality and failure to pupate render 

 conclusions uncertain, the relative number of individuals emerging and 

 the length of their pupal life may be taken as some evidence of the eftects 

 of evaporation when other conditions are considered. Accordingly, the 

 data are shown: In 1917, temperature 79°, humidity 75 per cent, evapora- 

 tion 4.3 cc. per day seemed most favorable. In 1918, temperature 58°, 

 humidity 60 per cent, evaporation 30 cc. per day seemed most favorable. 

 In 1919. first generation, temperature 80.2°, humidity 70 per cent, evapora- 

 tion 8.1: (lowest) cc. per day seemed most favorable. In 1919, second 

 generation, results were contradictory. In 1920 first results were con- 

 tradictory, due to mortality. In 1920, one set, the shortest time was with 

 6G.8 cc. evaporation, but this also showed the greatest failure to pupate. 

 The 1920 second generation showed temperature 82°, humidity 77 per 

 cent, evaporation 28.5 cc. to be best on the whole, although one rate was 

 higher and four were lower. It appears that higher failure to pupate and 

 higher mortality are accompanied by shortest pupal life under conditions 

 of very rapid evaporation. 



Tahle XXVIII. Showing the emergence of moths from hihernated larvae 



(1920-21). 



All were kept at the same temperature during hibernation (37-48°) until March 



15th, when the temperature was raised to 73.5° F. 



