Plate 18; Seed, Plate 27, Fig. 30.
Botanical description: Red Clover is mainly biennial. The year the seed germinates, only short leaves and stems are produced and no flowers. The second year the flowers are developed and the seed formed, and after ripening the seed the plant dies. As with most biennial plants, the root is a taproot; that is, the single main root gradually tapers downward and produces numerous side branches. On these are developed the small, rounded or egg-shaped nodules which contain the bacteria necessary for the proper development of the plant. From the upper end of the taproot, which is somewhat enlarged and generally known as the crown, are formed more or less numerous buds which develop into leafy stems. These as a rule are from one-half to two feet high, strictly upright or ascending from a decumbent base, the latter being the normal growth of stems developed from the outer margin of the crown. The stems are generally branched above the middle and the leaves are single at each joint. The three leaflets of which each leaf consists are oblong or egg-shaped and usually marked with a white spot of varying size and shape. The stipules (see page 15) attached to the base of the leaf stalk are triangular at the base and suddenly contracted into an awnlike point. This peculiar shape is a characteristic by which Red Clover can be readily distinguished from Zigzag Clover* (Tri-folium medium L.), which it closely resembles and is often confused with. The stipules of Zigzag Clover are narrow throughout. The Red Clover flowers are in a dense head, which is about an inch in diameter when fully developed. They vary from bright red to purple but are sometimes white.
* Zigzag Clover, so-called after the zigzag bending of the stems, has much narrower leaves than has Red Clover. It is a perennial plant, common in Europe where it grows along borders of woods and in open woodlands. The so-called Simpson's Perennial Red Clover from Prince Edward Island and Couch Grass Clover from the Maritime Provinces are of this species.
Plate 18 RED CLOVER ( TriFolium pratense L.).
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 becomes 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, theordinary honey bee is not able to gather honey from Red Clover, its proboscis being far too short. In spite of this, however, tin- ordinary honey bee is of considerable importance in the fertilization of
Red Clover. Though it cannot reach the honey, it can reach the pollen, and when securing this for bee bread it comes in contact with the pistil and thus has an opportunity to assist fertilization.
The result of the fertilization of the flower is the development of a small, straight pod containing one seed. When fully ripe this is released by the falling off of the upper caplike part of the pod.
Red Clover and all other species of the genus Trifolium behave in a rather peculiar way after flowering. Their flowers do not fall off but remain withered on the head during the whole season, giving the ripened heads their characteristic brown appearance. This peculiarity makes it easy to distinguish the genus Trifolium from the genus Medicago, the flowers of the latter not being persistent. The pods of Alfalfa and other species of Medicago are exposed while ripening, whereas the pods of Red Clover and other species of Trifolium are not visible.