JOSEPH KRATKA., JR. 461 



causal factor, extreme temperature, had been removed. To this phenomenon 

 Woltereck gave the name of "induction" or "pre-induction" according to the 

 number of generations involved. 



No such effect as this was noted in connection with facet number 

 as investigated in Experiment 51. It is possible, however, that by- 

 continued existence, generation after generation, at a high or low 

 temperature, such an effect might be obtained. 



Temperature as a Causal Factor in the Production of Mutations. 



Tower found among his potato beetles color variations that persisted through 

 subsequent generations. Presumably, since they were reared at high tempera- 

 tures, the cause of the mutation lay in this fact. 



The present study shows marked discontinuous variations at 

 neither high nor low temperature. Temperature in the present 

 study is not a factor in the production of mutations. 



SUMMARY. 



Three strains of the bar-eyed mutant of Drosophila melanogaster 

 Meig have been reared at constant temperatures over a range of 

 15-3rC. 



The mean facet number in the bar-eyed mutant varies inversely 

 with the temperature at which the larvae develop. 



The temperature coefficient (Qio) is of the same order as that for 

 chemical reactions. 



The facet-temperature relations may be plotted as an exponential 

 curve for temperatures from 15-31°. 



The rate of development of the immature stages gives a straight 

 line temperature curve between 15 and 29°, Beyond 29° the rate 

 decreases again with a further rise in temperature. 



The facet curve may be readily superimposed on the development 

 curve between 15 and 27°. 



The straight line feature of the development curve is probably 

 due to the flattening out of an exponential curve by secondary factors. 



Since both the straight line and the exponential curve appear 

 simultaneously in the same living material, it is impractical to locate 



