[Illustration: Fig. 5.--Individual racemes of white sweet clover covered with cheesecloth to protect them from insect visitation.]
Table II.--_Treatment of sweet-clover flowers in the artificial-manipulation experiments._
------------+--------------------------------------------------------- Experiment. | Method of pollinating the flowers. ------------+--------------------------------------------------------- A | Check--covered. | B | Check--open to insect visitation at all times. | C | A separate toothpick was used to spring the keel of each | flower on the raceme. | D | One toothpick was used to spring the keels of all the | flowers on a raceme. | E | Cross-pollinated. | F | Raceme rolled several times between thumb and finger. ------------+---------------------------------------------------------
As insects, and especially honeybees, usually visit all recently opened flowers on a raceme, experiments C and D were conducted to determine whether more seed would be produced when pollen from other flowers on the same raceme was placed on the stigmas of the flowers than when only the pollen produced by each flower was placed on its own stigma. The effect of pollination when only the pollen produced by an individual flower was placed on its own stigmas was also obtained in experiment F, as by this method of pollination no pollen was transferred from one flower to another. It can not be stated definitely that the seed produced by the cross-pollinated flowers was the result of fertilization with foreign pollen, as the anthers were not removed from the flowers pollinated because it would be necessary to remove the anthers when the flowers were not more than two-thirds mature, and in doing this the flowers would be so mutilated that only occasionally would pollination at this time or at a later date be effective. The flowers listed in experiment E were pollinated a short time before they opened, and in each case pollen taken from flowers of other plants was placed on the stigmas. The petals of the cross-pollinated flowers were not mutilated, and in each case they returned to their original positions soon after pollination. The results obtained in experiment B, where the racemes were simply labeled and left open to the action of insects at all times, serve for comparison with other experiments where the flowers were protected from insect visitation and were artificially manipulated.
