PLUM, the popular name for several spe cies of the genus Prunus, extensively cultivated in mild climates for their fruits. They are widely distributed in the North Temperatezone, especially in America and eastern Asia. "They have alternate, simple, leaves; white flowers mostly in cymes and generally appearing with the leaves; and drupaceous, one-seeded, bloom covered fruits. They are closely related to apricots, cherries and peaches.
The most important species is the European plum (Prunus domestica), a native of the Cau casus region, and thought to have been derived from the blackthorn (P. spinosa). It has given rise to four distinct groups: Prunes, firm, thick fleshed, sweet varieties of various colors (blues are best known), adapted for drying without the removal of the stone (see PRUNE) ; Damsons, little, firm-fleshed plums of diverse colors and usually clustered, frequent in fence corners; Greengages, small green, globular plums gen erally of high flavor; Large, yellow, blue, red and purple varieties. The domestics are the leading plums from New England southward to Pennsylvania, westward to Lake Michigan, and upon the Pacific Coast. Some of the hardier Russian varieties are being tried in the colder regions of the West and North.
Next in importance are the Japanese varie ties of Prunus triflora, first introduced into America in 1870. This species is presumably a native of China. The fruits are generally rounder than those of the domestica varieties, and are more noted for their light reds and yellows. Their chief merits are: added variety to the list, especially of early maturing kinds, firm-fleshed fruits which ship well and vigor ous, productive trees freer from the attacks of curculio and black knot (see below) than the domesticas. They succeed farther south than the domesticas, and in many instances farther north.
Several American species have also rapidly become popular in the United States and Canada. Prunus americana and P. angustifolia are the leading species, the former especially in the North and West, but also extending to the Gulf States; the latter popular from Pennsyl vania southward. These are of still more recent introduction into cultivation than the Japanese varieties, and are valuable acquisitions where the two preceding groups fail. The wild goose plum is P. hortulana.
The following species are also cultivated: Myrobalan or cherry plum (P. cerasifera), pre sumably a Caucasian species, used largely by nurserymen for budding plums upon; apricot or Simon plum (P. simonii), an introduction from China popular in California since 1880, but little grown in the East ; beach plum (P. marl lima), common upon the coast from Nova Scotia to Virginia, but little cultivated except as an ornamental shrub; Pacific Coast plum (P. subcordata), indigenous in Oregon and Cali fornia, and somewhat cultivated; and the sand plum (P. angustifolia watsoni), a shrubby
species common in Kansas and Nebraska, but little cultivated.
Plums are propagated from seed only when new varieties are desired; varieties true to name are all propagated by budding or, to a very limited extent, by grafting. The process is the same as for the peach (q.v.). If domes Lica varieties are to be grown upon light soil they are generally whip-grafted on peach stocks, the peach being adapted to such soils. Similarly peaches to be grown upon heavy soil are often grafted upon plum stocks.
The various groups succeed upon a wide range of soil; the domesticas are generally well adapted to heavy soils; the Japanese to medium and even light; and the American kinds often to very light. There are, however, varieties in each group adapted to other soils than suit the majority. The land is deeply plowed and thoroughly harrowed before planting. The trees are set about 20 feet apart in squares or hexa gons (see PEACH), or in rectangles from 8 to 12 feet asunder in rows 18 to 20 feet apart. In the last case cultivation is given only one way when the trees commence to touch. Usu ally less than half a dozen main limbs, prefer ably close to the ground, are allowed as the framework of the tree and after the first year or two little pruning beyond the removal of interfering, injured or dead 'branches is given. The trees are usually planted when two years old from the bud, extra vigorous growers some times when one year old. Varieties of the Japanese and American groups should not be planted in blocks of only one kind, since they are often self-sterile and fail to set fruit; two or more kinds should be alternated in the or chard. (See PEAR). Cultivation is practically the same as for apples and pears. In the West ern States, however, a mulch of straw, marsh hay, etc., is often substituted for cultivation. The fertilizers usually employed are rich in potash and phosphoric acid. Cover crops of legumes should supply sufficient nitrogen, or a biennial dressing of stable manure may be used as a supplement. Occasional dressings of lime are often beneficial. Few fruits respond better to liberal feeding than the plum. The conserva tion of plant food which follows thinning the fruit, to stand at least two inches apart, is also of great benefit to both tree, annual pro ductivity, size of fruit, and in the prevention of fruit rot. (See PEACH). When fully grown and colored but before becoming soft the fruits are gathered and generally marketed, in the East, in eight-pound Climax grape baskets. The plums shipped to eastern markets from Cali fornia (mostly of the prune and Japanese types) are packed in boxes and sent by refrig erator express freight.