162 



HAROLD H. PLOUGH 



trol given in No. 5. These weighted values for the black-purple 

 region are given in the center column in table 8. 



Alone and unrelated to any other set of data, the differences 

 between No. 4 and No. 5, No 5 and No. 7, and No. 8 and No. 9, 

 would not have great significance. When the table is taken as 

 a whole, with the values properly weighted by their corresponding 

 controls, it becomes clear that the curve presents a consistent 

 picture of the amount of crossingover in the second chromosome 

 between the minimum and maximum points at which fertile 

 offspring can be secured. At 5°C. negative results were shown, 



Percentage of 

 crossing over 



9 13 17.6 22 27 29 31 32 Degrees C 



Fig. 3. Weighted values for black-to-purple region in table S plotted to show 

 the effect of temperature on crossingover. 



for though a few pupae appeared in the bottles, no flies hatched. 

 Similar negative results were given at the high point 35°C, 

 except that in this case several females hatched but on being 

 tested were found to be entirely sterile for the first ten day 

 period. This can mean only that the eggs which went through 

 the growth period while the female parent was pupating were 

 injured in some way by the high temperature and did not develop. 



Discussion of temperature curve 



The establishing of such a curve is of some practical value 

 for the reason that it shows the approximate limits in degrees C. 

 between which bottles must be kept to be comparable. When 



