39!) 



For lf)16, the hibernated generation showed first pupation on April 

 13 and last emergence June 17. The mean substitution-quotient was 2t)9 

 and the mean alflia value was 52° F. The first generation began pupating 

 June 20 and ended September 11, with a mean quotient of 2(i6 and a mean 

 alplia value of 50.1:° F. The second generation consisted of 46 individuals 

 (August 28 to September 27) divided into two groups: 30 with a mean 

 of 246, and 2T with a mean of 277. The mean alpha value is 50.9° F. 



For 1917, the hibernated generation (first pupation April 3, last 

 emergence June 21), at Olney, gave a mean of 276 and a mean alpha 

 value of 51.7° F. The first generation (first pupation June 27, and last 

 recorded emergence August 6) gave a mean of 249. The second genera- 

 tion mean was 254 for 7 individuals. The mean alpha value was 50° F. 



The mean of all generation means for the Olney data was 266 (sub- 

 stitution-quotient). Omitting third generations and the 1917 second 

 generation, it was 272. 



The substitution-quotients for the Champaign data with the number 

 of individuals shown in parenthesis were as follows: 

 Summer 1917 (15) 267 



Summer 1917 (5 ) 271 



Spring 1918 (26) 275 



Summer 1919 (2 ) 263 



Summer 1919 (4 ) 272 



The mean substitution-quotient, when the different generations and 

 experiments on different generations are considered separatelv. is 206 ; 

 with the third generation omitted, it is 270. The mean alpIia value is 

 approximately 51.0° F. The lowest value was 49.8° and the highest was 

 52.5° (at Olney) and 52.9° (in a variable-temperature experiment). 

 These alpha values have no physiological significance. They are merely 

 important in calculation work. The value is fixed by the ratio between 

 velocities at high temperatures and those at low.* The actual threshold 

 is lower, probably as much as 9° F. ; development drops ofl: slowly at the 

 lowest temperatures. 



Variation in the substitution-quotient is illustrated by a comcarison 

 of the two groups of 1915 pupae. Those appearing on May 14 and 

 emerging June 4 (time 21 days) had a quotient of 28/ ; while those 

 appearing August 17 and emerging September 3 (time 17 days) had a 

 quotient of 24J. A comparison of Figs. 21 and 22 shows that the dis- 

 tribution of temperature and humidity is about the same for the mass of 

 readings. Very radical changes in the equal-velocity lines would be nec- 

 essary to make the quotients alike. The velocity curves (see Fig. 20) 

 were identical. The standard time (mean velocity per day divided into 



•Variation in the alpha value may be illustrated as follows: Through the two 

 natural group.'i of dots on Fig'. 17, draw two lines (for example, one from H 45 ^o 

 T 8S° to H 75% T 67°, and the other from H 35% T 96° to H 70% T 50°) ; plot any 

 two velocity values crossed by each line against the corresponding temperatures on 

 the scale, and produce the line joining these two plotted points to the temperature 

 axis ; note the alpha values thus obtained. 



