200 
HAROLD H. PLOUGH 
for this conclusion is stated to be found in a calculation of the 
coincidence values for my two-day-interval experiment for the 
black-purple-curved region reported in my former paper. They 
state (p. 199) : 
In this experiment the curve of variation in coincidence was the 
mirror image of the curve of variation (in crossing over) for age. The 
curve of coincidence corresponding to the curve of temperature varia- 
tion found by Plough seems to be a straight line cutting the rises and 
falls of the temperature curve and independent of them. 
TABLE 4 
Coincidence values for control and heat-treated lines in two-day-interval experiment. 
{For actual counts cf. Plough, '17, table 14) 
b pr c 
NUMBER DATS 
CONTROL— 22°C 
CON-TINUOCSLT 
PARENTS HATCHET) AT 22°C., EXPOSED 
TO 31.5°C. FROM 3rd to 11th DAT 
AFTER MATING 
Per cent of crossing 
over — b, pr region 
Coincidence 
b, pr-pr, c 
Coincidence 
b, pr-pr, c 
Per cent of crossing 
over— b, pr region 
3 
8.3 
0.91 
1.01 
7.1 
5 
4.9 
0.94 
1.31 
4.8 
7 
6.8 
1.13 
0.53 
3.8 
9 
5.8 
1.03 
1.37 
3.8 
11 
4.2 
1.06 
0.63 
8.8 
13 
5.1 
0.80 
0.94 
13.9 
15 
5.3 
1.40 
0.99 
19.2 
17 
4.2 
0.92 
0.95 
20.0 
19 
7.3 
0.93 
0.73 
17.5 
21 
8.2 
1.04 
1.57 
6.8 
23 
7.9 
0.63 
0.27 
4.9 
25 
7.0 
0.98 
1.4 
I have calculated the coincidence values for the experiment 
cited and the results are given in table 4. A comparison of my 
coincidence values with the crossover percentages for the black- 
purple region shows that the coincidence value varies within 
rather wide limits in both the control and experimental lines. 
A smoothed curve gives some suggestion of the relation claimed 
by the writers quoted, but its significance is doubtful. The same 
comparison may be made between the similar lines in chromo- 
some III (table 3). The coincidence values for the diiTerent 
pairs of regions are given in the last three columns. Here there 
