EFFECT OF TEMPEEATURE ON CROSSING OVER 
195 
crossing over, so that no result appears in the count. With the 
exception of these two regions, in which Bridges ('15), Plough 
('17), and Bridges and Morgan ('19) have recorded an age differ- 
ence^ the diagonal lines also indicate the regions which show a 
variation in crossing over with age. 
O.O-M-Star S 
24. -cut 
^.4. .Termlllon 
49.0- -garnet 
'ftl.S-i-forked 
Chromosome I 
46.8- -black 
purple — 
vestigial 
sepia 
11.4 ^Dlchete 
^7.8- spineless 
sooty 
^1.9 •■■roueh 
Chromosome III 
185.5 J-speck 
Chromosome II 
Fig. 3 Chromosome maps showing all the important regions whose reaction 
to high temperature has been tested. The regions which show a significant in- 
crease in crossing over after exposure to high temperature are ruled with diag- 
onal lines those not affected are solid black. The coincidence values are given 
outside of brackets enclosing the different pairs of adjacent regions. 
I have recently laid some emphasis on the fact that in the 
sensitive section of chromosome II the percentage of increase 
in crossing over due to high temperature was roughly in inverse 
proportion to the length of the region involved (Plough, '19). 
The results in chromosome III demonstrate very plainly, however, 
