CROSSINGOVER IN DROSOPHILA 



153 



Starvation 



A second test gave no more significant result. Pairs made up 

 as in the previous set of data were successively placed in the 

 bottles of two series, Series A being the control. In the bot- 

 tles of Series B about one-tenth of the usual amount of food was 

 placed. After several days this food was crowded with larvae 

 and very soon became thoroughly dry. The few female flies 

 which hatched from these cultures had pupated while very 

 small and were under-sized. The back-cross, however, showed 

 little difference in the amount of crossingover. 



TABLE 3 

 b — pr — c 



Control. 

 Starved . 



per cent 



21.5 

 19.1 



Increased fermentation of food 



It was conceivable that the amount of fermentation which the 

 food had undergone might have some effect since this was known 

 to be a rather variable quantity. For the purpose of this experi- 

 ment the Pi parents were divided into two groups. Two series 

 were made up with approximately the same amount of the same 

 batch of food in each. Series A was the control, and into the 

 bottles of Series B an even teaspoonful of chemically pure 

 dextrose was placed. The bottle conditions in Series B were 

 markedly better than in Series A, and uniformly larger broods 

 hatched from the former, although approximately the same 

 number of eggs must have been laid in all of the bottles. The 

 crossingover tests of females hatched under these conditions, 

 however, showed differences which have so little significance 

 that the probability that they are the same is 38 in 100. The 

 summaries are as follows: 



