COWPEA. Vigna unguiculata, Walp. Leguntinosce. Figs. 370, 371.
A summer-growing annual more closely related to the bean than to the pea, grown for forage, for green-manuring and cover-cropping, and sometimes for human food. The habit of the plant varies greatly, some varieties being erect or bush-like and others distinctly trailing. All intermediate forms occur, and the habit is dependent not only on variety, but on soil, time of planting and climatic conditions. The cowpea is never a true climber, being without tendrils, but its slender runners twine around adjacent objects. The leaves are three-foliolate, and somewhat similar in shape and appearance to those of the common garden bean. The flowers are usually whitish or whitish purple, some times with a yellowish cast. The pods are normally of straw color, but are sometimes purplish or dark. They vary in length from five to ten inches and contain numerous edible seeds. The seeds are usually kidney-shaped or roundish, but in some varieties the ends are slightly truncated.
The cowpea, although belonging to the genus Vigna, is closely related to species of the section Strophostyles of Phaseolus. It is a native of India and the region northwestward to thesouthern part of the Trans-Caspian District, but has been a cultivated crop for two thousand years or more. It was intro duced into the West Indies in the latter half of the seventeenth century, and began to be cultivated on the mainland of America somewhat later. At various times the cowpea has been known under several botanical names, the most common names being V. Sinensis and V. Catjang. The American varieties of the cowpea, however, are correctly classified as V. unguiculata (V. Sinensis), while the name V. Cat jang properly applies to another species easily distinguished by its much smaller and more torose pods, and by its smaller seeds. By some, however, V. unguiculata is considered to be a synonym of V. Catjang.
Varieties of cowpeas have become widely dis tributed throughout the world, but only in China, India and the southern part of the United States has this plant been an important factor in agri culture. Although cultivated in the United States for about a century, not until recent years has its cultivation received much attention north of the Ohio and Potomac rivers, and north or west of Ar kansas and Texas. Within the past ten years, stim
ulated by tests made at the various agricultural experiment stations, the cultivation of the plant has been carried northward, and it now promises to fill an important place throughout the greater part of the humid United States. The northern limit of cultivation has never been traced in detail, but in a general way this area may be regarded as including the states of Massachusetts, New Jersey, Pennsylvania, much of New York, Ohio, Indiana and Illinois, all of Missouri, Kansas, Oklahoma and Texas, and of course the region south and east of these states.
Westward of this line it may serve a useful pur pose, but can scarcely compete with alfalfa or red clover where these plants are generally successful.
The seed of the cowpea is rather uniform in composition and is very rich in nitrogen, but not so rich in this element as is soybean seed. The forage varies considerably in composition because of the variation in the quantities of pods and leaves.
The cowpea is subject to such wide and easy variation as the result of climate and other envi ronment that any treatment of varieties is unsat isfact fry. More than one hundred different names are on record purporting to be names of varieties, but in reality many of these are synonyms. Dodson states (Louisiana Experiment Station, Bul letin No. 401 that there are probably about five botz.nical varieties, namely, those with (1) red seed. (2) black seed, (3) white seed, (4) the clay varieties, and (5) granite and similar strains, with fine, dark markings on a brown background. He regards all others as connecting links or inter mediate hybrids. However, we must recognize a considerable number of true agricultural varieties, with fairly good distinctions. whatever may have been their origin. Perhaps the best attempt to classify any considerable number of varieties was that made by Starnes in Bulletin No. 26 of the Georgia Experiment Station, which classification is here quoted : "Among the more important characteristics which distinguish the different varieties are the following, in the order of their probable impor tance: (1) Form of pea.