RED CLOVER. 99
Biology of flower: If Red Clover is isolated during flowering time, so that no insects can visit the blooms, no seeds will be formed, as it depends upon insects to transport the pollen from one flower to another. Bumble bees, which visit the flowers in order to secure the nectar, are especially active in this transportation. The blossoms of Red Clover are peculiarly sensitive; when a bumble bee in search of honey forces its proboscis down and touches the lower parts of a flower, such a touch, if the flower is fully developed, makes the stamens and pistil protrude from the interior of the blossom into the open air. The bending of the stamens and pistil brings their upper ends into close contact with the body of the insect, which thus be-comes powdered with pollen from the stamens. The pistil protrudes a little beyond the stamens. This might seem an insignificant fact, but it means that the pistil has a better chance to come in contact with the pollen from other plants, already deposited on the body of the insect, than to come in contact with the pollen of its own flower. As the insect travels from one plant to another, carrying pollen from different individuals, the pistils of one are apt to be fertilized by pollen from another. Such cross-fertilization must, in fact, take place before seed can be developed. In other words, Red Clover is completely self-sterile. The pollen is unable to fertilize the pistils of the plant on which it is produced.
As a rule, the insect carries enough pollen from different individuals to give the pistils an opportunity to be powdered from other plants. There is, however, a chance that a single visit from one insect would be insufficient. To provide a greater opportunity for every flower to be fertilized, nature has made it possible to have each Red Clover blossom visited by insects many times. In Alfalfa each flower has only one chance to be fertilized (see page 115), as the stamens and the pistil, after the explosion of the flower, do not return to their original positions. A Red Clover blossom has many chances, as the pistil and stamens protrude for only an instant, after which they move back to their original positions. Their sensibility is not lost after the first visit of an insect; a second or third visit will have the same effect, and the chances of the pistil being properly fertilized will last as long as it remains in a condition to receive the pollen.
Bumble bees are the only insects, with the exception of some butterflies, with a proboscis long enough to reach the nectar at the bottom of the flower tube. As is well known by bee-keepers, the ordinary honey bee is not able to gather honey from Red Clover, its proboscis being far too short. In spite of this, however, the ordinary honey bee is of considerable importance in the fertilization of