26 



BULLETIN" 289, TJ. 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 1911. 



No. 



Heads 

 worked. 



Brush 

 used. 



Treat- 

 ments. 



Seeds 

 per head. 



Plat 9, check 



532 

 470 

 432 

 460 









Plat 10, check 







50.9 



Plat 11 



A 

 A 



3 

 3 



39.2 



Plat 12 



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 man}' 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 infertile 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-pollinated 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 



