338 



mental total and using it as a standard. For the constant-temperature 

 experiments within the straight-line limits, the average total was (),93(i 

 developmental units for the pupa, and for the variable-ttmperature 

 experiments it was smaller, approximately 6,480 (average by two 

 methods). This variable-temperature total, 6,480, was used as a normal 

 in adjusting the velocity values outside the straight-line limits, because 

 ordinary weather conditions are variable with respect to temperature, 

 etc.. and result in more rapid development. This normal total for the 

 pupal stage was verified by elaborate calculations covering all of Glenn's 

 Olney data. Similarly, normal totals were established and verified for 

 the other stages. 



The developmental totals used herein are not comparable to the 

 sums of "effective day-degrees" commonly used in direct applications 

 of weather data, for developmental units are not temperature units 

 but are numerical expressions of the response of the organism to 

 temperature and all other conditions, a response which is usually 

 growth or an internal change leading to transformation from one 

 stage to another in the life-cycle. These developmental totals, being 

 based on the pheno-hour, are in accord with the concepts of phenology 

 which take into account both weather and the responses of organisms. 



Calculation of Standard Time. 



In order to compare the results obtained by this method with 

 those obtained by the old method of summing "effective temper- 

 atures", it is convenient to express the conditions of development in 

 terms of the substitution-quotient, which is approximately equal to 

 the number of "degree-days" summed for medial temperatures. (See 

 PART THREE, p 391 fl:". This practice has been followed in Tables 

 VTI-XI, in which all of Glenn's Olney data and his Urbana data on 

 pupae are recalculated in terms of standard velocity values. These data 

 were used in the calculation of standard time for each stage, as follows : 



Starting with the date of the observed beginning of each stage in 

 each generation in each year, as recorded by Glenn, velocity values (Table 

 I) were set down for the mean temperatures and humidities for all two- 

 hour periods as shown in his hygrothcrmograph records for the several 

 years covered by his work; the numbers of developmental units (velocity 

 values multiplied by 2, because two-hour periods were being used) were 

 then summed to normal totals, and dates were thus obtained on which the 

 several stages in each generation should have been completed if these 

 velocity values and developmental totals were normally fulfilled. In order 

 to calculate the theoretical time for each individual or groi\p of individuals 

 behaving alike, the sums of developmental units for each day from the 

 beginning of a stage to the actual date of its completion were then aver- 

 aged, and this daily mean was in each case divided into the normal 

 developmental total, so as to give a number of days approximating the 



