26 BULLETIN 289, U. S. DEPARTMENT OF AGRICULTURE. 
three days apart in the forenoon were given. The results are pre- 
sented in Table X. 
TaBLE X.—Average seed yield per head when brushes were pressed together below the clover 
heads and pulled upward, summer of 1971. 
NG Heads | Brush Treat- |° Seeds 
Se worked. used. ments. | per head. 
lati CNeCkit see Se te oe eee ee eee 552 Pigs see: | fig EEE era 55.4 
Plat 10: Check. <= S.. vay Ia ate pee a ence ea Ap |x eee lee Sareea 50.9 
fd od eae tal eet Wi ara ioe os ee Ree eg ok aa pans 432 A 3 39.2 
Ard Pee oe Pere erie Reems See en ss abe aS 460 A 3 40.9 
Table X shows that this manner of treatment as well as the hori- 
zontal and vertical stroke treatments caused a decrease in the pro- 
duction of seed. 
SUMMARY. 
A study of the cytology of red-clover flowers shows that many of 
them contain infertile ovules. The percentage of infertile ovules is 
greater in the first crop than in the second crop. In the first crop 
many plants produce 100 per cent of infertile ovules, while in the 
second crop the percentage of infertility ranges from none to a high 
figure. The percentage of infertite ovules in red clover is probably 
correlated with moisture conditions. 
The pollen grains of red clover are very sensitive to moisture, 
On account of this, there can be little effective pollination when the 
flowers are wet. Germination of the pollen grains takes place only 
within a limited range of variation in the water supply. It is prob- 
ably true that the only function of the stigma is that of supplying the 
requisite amount of water to the pollen for germination. 
The time between pollination and fertilization varies with the 
temperature of the atmosphere. The time between pollination and 
fertilization in July is approximately 18 hours, while in October it 
varies from 35 to 50 hours. An examination of 30 flowers which had 
been self-pollmated for 55 hours showed good germination on the 
stigmas but no fertilization. The pollen tubes made a slow growth 
and none exceeded 4 mm. in length. In flowers which had been 
self-pollinated for 90 hours one pollen tube attained a length of 
7.5 mm., while the rest were 5 mm. or less in length. The pistils of 
red clover average about 12 mm. in length. Eggs were found to be 
disintegrating four days after the flowers opened. 
The self-pollination and cross-pollination experiments which were 
conducted in the field checked up very closely with the results 
obtained from the cytological studies. The average yield of seed 
obtained on heads which were not pollinated and on heads which 
were self-pollinated in different ways was less than one-half of 1 per 
ee ee ee ed 
204 ates 
fine § 
