Martin (25) found the setting of alfalfa seed and Westgate (40) found the setting of red-clover seed to be affected by an excessive quantity of moisture in the soil or atmosphere. In order to overcome the possible effect of this or of other detrimental factors, in each experiment only the flowers on a certain number of racemes were pollinated at one time. All of the experiments were repeated a number of times during the months of July and August, 1916, and the results given in Table III show the total number of flowers pollinated and the number of pods that formed during the two months.
The results presented in Table III show that flowers fertilized with pollen transferred from another plant produced a higher percentage of pods than any of the other treatments. The results obtained in experiment D, where the same toothpick was used to spring the keels of all the flowers on a raceme, show that this method of pollination produced an average of 7.24 pods per raceme more than the racemes in experiment C. where a separate toothpick was used for each flower. These results indicate that pollen transferred from one flower to another on the same raceme is more effective than when the pollen produced by an individual flower is used to fertilize its own stigma. However, the results of experiment C prove that self-pollination is effective in _Melilotus alba_. In experiment B. which was the open check, 4.3 per cent more flowers set seed than on the racemes where the same toothpick was used to spring all the keels, but 11.57 per cent more seed was obtained than in experiment C. Spontaneous self-pollination occurs to only a very small extent, as will be seen from the results of experiment A, in which an average of only 2.9 per cent of the flowers set seed.
Table III.--_Effect of different types of artificial manipulation on the seed production of sweet clover at Arlington, Va., and at Ames, Iowa, in 1916._
----------+--------+---------------------------+------------------- | | Total number of-- | Flowers that set | | | seed (per cent). | Experi-+--------+--------+---------+---------+--------- Location. | ment. |Racemes.|Flowers.|Pods set.| At each | | | | | | station.| Average. ----------+--------+--------+--------+---------+---------+--------- | | | | | | Arlington | A | 49 | 3,510 | 144 | 4.1 |} 2.9 Ames | A | 84 | 4,536 | 92 | 2.0 |} | | | | | | Arlington | B | 100 | 5,599 | 3,973 | 70.95 |} 66.51 Ames | B | 196 | 1,276 | 600 | 47.02 |} | | | | | | Arlington | C | 50 | 1,229 | 701 | 57.03 |} 54.94 Ames | C | 75 | 289 | 133 | 46.02 |} | | | | | | Arlington | D | 50 | 1,480 | 936 | 63.24 |} 62.18 Ames | D | 88 | 575 | 342 | 59.47 |} | | | | | | Arlington | E | 31 | 377 | 307 | 81.43 |} 70.10 Ames | E | 48 | 175 | 80 | 45.71 |} | | | | | | Arlington | F | 30 | 933 | 524 | 56.16 |......... ----------+--------+--------+--------+---------+---------+---------