FACTORS INFLUENCING FLOWER SIZE IN NICOTIANA 36 1 
spread of the "younger" flowers averages 3.18 zt .17 mm. smaller than 
the spread of "older" flowers, while the length of "younger" flowers is 
slightly greater, 47 =b .11 mm., than that of the "older" flowers. 
This condition is undoubtedly due to the indirect method of comparison 
which we have here adopted and not to any actual shortening of the 
corolla tube. At the same time it renders even more significant the 
increase in corolla spread after anthesis which was found in measure- 
ments on the same flowers. This fact has been confirmed by direct 
measurements on a few individual flowers at these two stages in 
development. The length of time that intervenes between these two 
conditions in the flower is dependent to a considerable degree on 
weather conditions in the field, but in general occupies from 3 to 10 
hours. We may, therefore, state that the spread of the flowers on 
these Fi species hybrids increases distinctly within the period inter- 
vening between the opening back of the corolla limb and the dehiscence 
of the mature anthers, while, as might have been expected, the length 
of the corolla tube increases only slightly, if at all, during a corre- 
sponding period. 
Table XWa 
Frequency Distribution for Corolla Spread of Flowers of ij Fi Hm, 
Position 
Class Centers 
n M 
llimeters 
No. 
Mean 
Coef. Var. 
31 
32 
33 
34 
35 36 
37 
38 
39 
40 
On laterals 
On terminals 
I 
3 
10 
II 
ill 
14 
4 
13 
17 
I 
1 
9 
2 
65 
45 
38.09 it. 12 
34-67±.i9 
3.71 ±.22 
547±-39 
Difiference between means 
1 
3.42=t.22 
Table XIV6 
Frequency Distribution for Tube Length of Flowers of ij Fi Hut, 
Class Centers in 
Millimeters 
Position 
No. 
Mean 
Coef. Var. 
47 
48 
49 
50 
51 
52 
S3 
54 
55 
56 
57 
On laterals 
4 
6 
20 
21 
14 
65 
55-54±-09 
2.00±.I2 
On terminals 
I 
3 
4 
8 
6 
12 
8 
2 
45 
52.IIzb.2O 
378±.27 
Difference between means . 
1 
3.43 ±.22 
The second point under the "age of flower" factor is illustrated 
in Tables Xllla, XIII&, XlVa, Xm, XVa, and XVb. For 13 (11) 
Fi H38 and 13 Fi H137 the flowers produced on the terminal inflorescences 
