Part 3

After the root system becomes established the plants produce an upright, branching, leafy growth, which under ideal growing conditions may reach a height of 48 inches the first season, but more often 18 to 30 inches. A large quantity of reserve food is stored in the tap-root the first season; this reserve food enables the plants to make a rapid and vigorous growth early the following spring.

Toward the end of the growing season of the first year a number of buds, which serve to produce the second year's growth (fig. 4), are formed on the crowns of the plants. After these buds are formed the plants may be clipped quite close to the ground, as the buds are not developed until the plants have made sufficient growth to live through the winter.

During the second season sweet clover makes a rapid, erect, stemmy, branching growth from 5 to 10 feet in height, the plants producing only a moderate number of leaves, which drop as the seed matures. A large number of loose racemes bearing white flowers (see fig. 2) are produced during the flowering period, which usually lasts from three to five weeks.

Before sweet clover has made a growth of 12 to 18 inches it closely resembles alfalfa. The plants may be distinguished from alfalfa by the absence of pubescence on the under side of the leaves and by their bitter taste. When they are in bloom they may be identified easily by their long, loose racemes of white flowers and their open, coarse growth. Unlike alfalfa, the seeds are ordinarily found singly in the pods. Two seeds may occasionally be found, and very rarely three, in a single pod.

STRAINS OF WHITE SWEET CLOVER.

A number of different strains of white sweet clover are to be found in the average field, but most of them are not as marked or as conspicuous as the different strains of red clover. The principal differences between strains of sweet clover are in leafiness, habit of growth, and date of blooming.

Occasional plants are especially heavy seed producers and bear many pods containing more than one seed. Other plants bloom earlier than the average date for white sweet clover, and it may be possible by selecting such strains to find one which matures early enough to produce two crops a season at high altitudes in the northern sections of the United States.

Fields of an exceptionally early blooming strain were found in Illinois, Iowa, and North Dakota in the summer of 1916. The plants were different in type of growth from the ordinary white sweet clover, being most conspicuous from the fact that they were in bloom during the first week of June, which is at least three weeks earlier than the ordinary species should bloom in these localities.

An annual white-flowered sweet clover was found in several localities in the fall of 1916. The seed which produced these plants was grown in Alabama. These plants resembled Melilotus alba in most respects except that they were strictly annual. They flowered and matured seed abundantly in South Dakota and North Dakota. It has not been determined whether this is a distinct species or merely an annual strain of the species mentioned.

BIENNIAL YELLOW SWEET CLOVER.

Biennial yellow sweet clover ordinarily is referred to in the seed trade and among farmers in regions where it is grown simply as yellow sweet clover. The plants of this species are somewhat more decumbent the first year, and ordinarily with more deeply notched leaves than the white-flowering species. Yellow sweet clover usually grows from 3 to 5 feet in height. This plant blooms from 10 to 14 days earlier than the white species, and for this reason it is advisable to sow seed of both plants when they are to be used for bee pasturage. On account of the finer stems of yellow sweet clover it is preferred in some localities for hay, but since it does not produce as much forage as white sweet clover and there is much less demand for the seed, it constitutes only a very small percentage of the total acreage. The much larger root growth of the white species, as illustrated in figure 5, is desirable because of the additional quantity of hummus added to the soil.

The seeds of the yellow species may usually be distinguished from those of other species, as some of them are slightly mottled with purple. The shape of the calyx, which is generally present on unhulled seed, and the venation of the seed pods also distinguish it. (See fig, 1.)

ANNUAL YELLOW SWEET CLOVER.

Annual yellow sweet clover, more commonly known as sour clover or bitter clover, is found chiefly in the South and Southwest. This plant is considered a noxious weed in grain fields throughout the Southwest. It is claimed that the flavor of the seed which is imparted to wheat can not be removed. Bakers decidedly object to this flavor, stating that it injures bread. Sour clover is grown rather extensively as a green-manure crop in orchards in portions of Arizona and southern California and when properly handled in these regions it has given profitable results. As the seed is obtained from the screenings of wheat, it is offered on the market at a very low price. Occasionally it is sold for the yellow biennial sweet clover. Seed of this plant should not be sown in any part of the United States except the extreme South or Southwest, and then only as a green hay manure crop. Where it is desired to plant sweet clover for pasturage or for the biennial white or biennial yellow species should be used.

OTHER SPECIES OF SWEET CLOVER.

Thirteen species of sweet clover have been tested by the Office of Forage-Crop Investigations to determine their economic value. With the exception of white sweet clover, yellow biennial sweet clover, and yellow annual sweet clover, but four species in the somewhat limited tests have given sufficiently good results to merit special attention, and none have so far proved superior to white sweet clover, which is now extensively grown in many States.

A species of Trigonella is often referred to as blue-flowered melilotus or blue-flowered sweet clover. While this plant is closely related to the plants belonging to the genus Melilotus, it does not belong to this genus and therefore should not be called sweet clover. It is an erect, quite leafy, very fragrant annual, which produces a fair growth. It may prove of value as a green-manure crop or as a catch crop under certain conditions, but at the present time it is not to be recommended where sweet clover can be grown successfully. In most tests Trigonella has produced less forage than the better species of sweet clover.

Trigonella caerulea.

HISTORY.

Sweet clover has been used as a honey plant and for forage and green-manure for more than 2,000 years in the Mediterranean region, although it has never been considered of much importance.

The first authentic report of sweet clover in the United States was in 1739, when Gronovius stated in his Flora Virginica that it was collected by Clayton. Cutler reported its presence in New England as early as 1785, and Pursh in 1814 stated in his Flora Americæ Septentrionulis that it is found on the gravelly shores of rivers from Pennsylvania to Virginia. Elliott reported the presence of yellow biennial sweet clover in his Sketch of the Botany of South Carolina and Georgia in 1824, and Beck found the species Melilotus leucantha in the Northern States in 1833.

Undoubtedly meaning Melilotus alba.

In 1856 Prof. Tutwiller, of Green Springs Academy, Ala., received a small quantity of white sweet-clover seed from the secretary to the United States consul in Chile. Part of this seed was planted by a young man named Stendwick on his father's plantation on the prairie limestone belt, where it flourished. This plantation later became the property of J. T. Collins who, realizing the value of this plant, sold seed to persons in many States. Not until recently has sweet clover been grown to any extent as a cultivated crop in this country.

DISTRIBUTION.

While sweet clover is to be found growing in many countries and on all the continents of the world, it is native to temperate Europe and Asia as far east as Tibet. It is grown to a limited extent in England, while in the eastern part of Scotland a small quantity is considered valuable in hay on account of its agreeable odor. The famous Cruyere cheese of Switzerland owes its flavor to yellow sweet clover. In Germany it has given very good results when used as a green-manure, while in parts of Russian Poland and Austria-Hungary it is grown as a green-manure, pasturage, and hay crop on poor soils. This plant is used for forage and as a soil-improving crop in the central provinces of India, while sour clover, commonly referred to as Melilotus parviflora, is credited with furnishing 75 per cent of the feed for the cattle of King Island, Tasmania, which produce the best beef and butter sold on the Tasmania market.

At the present time sweet clover is grown rather extensively as a field crop in the limestone regions of Alabama, Mississippi, and Kentucky, in northern Illinois, and throughout the western North-Central and Mountain States (fig. 6): in fact, it is grown as a cultivated crop to some extent in nearly every State in the Union. Comparatively little sweet-clover seed is sown in the Atlantic Coast States, since there the soils are for the most part acid, and heavy applications of lime will be necessary before sweet clover can be grown successfully. It is questionable whether this plant will ever be of much importance in the South Atlantic States, as cowpeas, soy beans, and crimson clover will make a fair growth on those soils in their present condition. The acreage of sweet clover probably will increase in the New England States, where it should prove of value as pasturage and as a soil-improving crop on soils where red clover no longer can be grown. Sweet clover grows abundantly in the limestone regions of northwestern New York.

A much larger acreage of sweet clover is grown in northern Illinois than in any other of the eastern North-Central States. The conditions in the western North-Central States and in the Mountain States appear to be particularly adapted to this crop. It is in that part of the country that the largest acreage is found, and, with the exception of the limestone regions of the South, that the least difficulty is experienced in obtaining a stand.

In those parts of the Mountain and Pacific Coast States, especially Utah, where it has not been tested carefully or where red clover or alfalfa can be grown successfully, sweet clover is looked upon as a weed. It may rightly be considered a weed in the irrigated regions of the West and Northwest, where it grows luxuriantly on ditch Banks. The dissemination of this plant in all parts of the country has been hastened by beekeepers who have seeded it in waste places for the production of honey.