360 IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
LENGTH OF COROLLA TUBES AND SIZES OF HEAD IN 
MILLIMETERS. 
First Crop Clover. 
No. Flowers 
- l 
2 ' 'i 
. ■ 
1 
! 3 
1 
4 
5 
6 1 
• ! 
a 
9 
10 
Average 
H eight 
of Head 
1 
10. 
I 9.5 
9. 
9.2 
9. 
9.4 
8. 
9. 
9.5 
9.2 
9.2 
27.5 
2 
8. 
8. 
7.5 
8. 
8. 
8. 
8. 
8. 
9. 
8.1 
8.1 
30. 
3— 
10. 
10.5 
10.5 
10.5 
10.5 
10. 
10.5 
9.5 
9.5 
11. 
10.25 
30. 
10 
10.5 
10. 
10. 
10.5 
11. 
11. 
10.5 
10.5 
10.5 
10. 
10.4 
31. 
13—— 
1 8.5 
! 8.5 
9. 
8.5 
8. 
9. 
9. 
8. 
9. 
8.5 
8.0 
23. 
Second Crop Clover. 
1 
8. 
7.5 
8. 
8.5 
7.5 
7.5 
8. 
8. 
9. 
8. 
8. 
22. 
3 
10. 
9.5 
11. 
10. 
10.5 
10. 
10. 
9.5 
9.5 
10. 
10. 
28. 
6 
12. 
12. 
12.5 
12. 
12.5 
12.5 
12. 
12.5 
12. 
12.2 
12.2 
12 
11. 
11. 
10.5 
10.5 
11. 
11. 
10.5 
11. 
10.5 
10.5 
10.2 
33. 
42 
9. 
9.5 
8. 
9. 
9. 
9. 
8.5 
9. 
9. 
9. 
8. 
31. 
45—— 
8.5 
8.5 
8.5 
8.5 
8.5 
9. 
8.5 
9. 
9. 
9. 
8.7 
31. 
The measurements reported by Pammel, and by us in 1911 
and those made by Rothschild and Frazier show a pretty close 
agreement. The longest corolla tube reported was of second 
crop clover. The general average is, however, somewhat shorter 
than first crop. This statement seems to bear out the one usu- 
ally made by beekeepers that the corolla tubes of second crop 
clover are shorter than for the first crop. The difference is, 
however, slight and the amount of nectar collected by honey 
bees from the second crop because of the shortness of the corolla 
tube is practically nil generally. 
It might, however, be noted that a number of investigators 
referred to in the paper, “Pollination Studies of Red Clover,” 
state that red clover is self fertile. This is not borne out by 
the studies of H. S. Coe referred to in the above paper; more- 
over, J. N. Martin in the same paper points out that sterile 
ovules in red clover are of common occurrence. “During the 
first crop many plants produce 100 per cent of infertile ovules, 
with such plants the presence of bees is not a matter of impor- 
tance for the ovules have no reproductive cells, hence there can 
be no fertilization and no production of seeds. During the sec- 
ond crop when the season is generally dry and favorable for seed 
setting, there is some infertility ranging from a low percentage 
or none in some plants to a high percentage in others. It is 
very probable that this infertility of ovules is to a greater or 
less degree a hereditary character and that the selection of a 
high yielding strain will consist, among other features, in se- 
