16 BULLETIN 2S9, IT. S. DEPARTMENT OF AGRICULTURE. 



covered, not treated, and used as checks in those experiments. 

 From the 757 heads covered and not treated in 1911 and 1912 an 

 average of 0.1 seed per head was obtained. The relatively high 

 average obtained at Altoona in 1911 may undoubtedly be accounted 

 for by grasshoppers mutilating the tarlatan which was used to cover 

 the heads. On this account heads were occasionally exposed to the 

 action of insects for a short time. 



Since no more seed was produced by these heads than may be 

 accounted for by insects working on the flowers when they were 

 occasionally exposed for a short time on account of rains or grass- 

 hoppers, we may say that clover flowers must be pollinated by some 

 agency before any seed is produced. 



EFFECT OF SELF-POLLINATION. 



Another experiment was conducted in which the clover heads 

 were covered with tarlatan before smy flowers opened and were kept 

 covered, except while being worked, until mature. As soon as the 

 flowers came into bloom they were self-pollinated by springing the 

 keels of the flowers with toothpicks, care being taken to rub pollen 

 upon each stigma. A separate toothpick was used for each head. 

 In 1911, 125 heads were seK-pollinated and 170 heads in 1912. An 

 average of 0.16 seed per head was obtained in 1911 and an average 

 of 0.09 seed per head in 1912. 



The results of this experiment show, as have previous experiments, 

 that red-clover flowers must be cross-pollinated in order to set seed 

 on a commercial basis. The amount of seed obtained is so small 

 that it was probably the result of bees working through the tarlatan, 

 although the cytological work reported upon in this bulletin shows 

 that it is possible to have an occasional seed produced from self- 

 pollination. 



SEED PRODUCTION OF HEADS UNDER ORDINARY FIELD CONDITIONS. 



As a field check on the preceding experiments a number of heads 

 were tagged in 1911 and 1912 and neither covered nor artificially 

 pollinated. These heads were labeled in different parts of the field 

 and Table IV shows the number of heads in each group and the 

 average seed yield per head. 



Tablk IV. 



— Average seed yit Id of clover heads not coven d or arti) 



Icially pollinated. 



Location and year. 



Number of 



beads 

 collected. 



Average 

 number of 

 seeds per 



head. 



Ames 1911 



300 

 532 

 170 

 150 

 65 



50. l 



Do. . 





Do 



50.9 



Altoona, L911 



43. 6 



Ames, 1912 



53. 4 







