350 



cause considerable deviation even if new velocity values were established 

 for this part of the larval life. 



e. Pupation after hibernation. 



It is possible to make only a rough, unreliable estimate of the time at 

 which larvae will begin to pupate after hibernation. This has been based 

 upon January 1 as an average date for the beginning of preparation for 

 pupation. The actual time of beginning has varied six weeks on either 

 side of this date in experimental stocks which were under identical condi- 

 tions except for varying amounts of moisture. This leaves an unsound 

 basis for a beginning, until the subject of hibernation has been thoroughly 

 investigated. It was hoped that the determination of the enzyme content 

 of larvae from time to time might indicate their condition relative to pupa- 

 tion, and the only enzyme, catalase, which has been investigated (see 

 below, p. 443), gave promise of results of value, but a definite correlation 

 has not yet been established. The work of Townsend ('26) has shown 

 that the amount of rainfall and the frequency of rains are of very great 

 importance. The whole subject deserves a thorough investigation. Re- 

 liable estimates of progress toward pupation in the spring of an unusual 

 year, when estimates are most needed, are not possible now. 



f. Pupae from Hibernated Larvae. 



The time of the first pupations will, for the present, have to be ascer- 

 tained from individual larvae under observation. The pupations are 

 strung out over a long period in spring. There are usually two maxima, 

 as shown in Glenn's charts 1, 2, and 3 and in Fig. 25 of this paper. In 

 Glenn's three cases the first maximum came eight to ten days after the 

 first pupation, and the second maximum came ten to twenty days later. 

 These maxima also occur under uniform temperature and after uniform 

 treatment (Fig. 25), but a correlation with weather is also shown by 

 Glenn's data. 



The Effects of Conditions Other Than Temperature and 

 Humidity. 



It is evidently possible to calculate time of appearance of stages and 

 to estimate progress to any date with a fair degree of accuracy from tem- 

 perature and humidity alone (Tables VII-XI). The calculation of 

 standard time for stages with respect to these two factors has another 

 important value, namely, the estimation of the efl^ects of otiicr factors 

 (amount and distribution of rainfall, seasonal march of mean daily tem- 

 peratures, solar radiation, etc.). Unfortunately, the responses of diiiferent 

 stages to these other factors are dift'erent, just as in the case with tempera- 

 ture and humidity. This renders it imperative that the different stages 

 be calculated separately. 



a. Rainfall. 



Autumn and winter rainfall has important effects upon the rate of 

 development of hibernated larvae and of pupae derived from them : when 

 rainfall is heavy, the larvae are more abundant, more of them pupate. 



