After the discussion of the characters of plums we may pass to a detailed description and discussion of the species of plums which now contribute or may contribute cultivated forms to the pomology of the country either for their fruits or as stocks upon which to grow other plums. The following conspectus shows as well as may be the relations of the species of plums to each other.
| A. Flowers in clusters of 1 or 2. (Three in P. triflora.)
Old World plums. | |
| B. Leaves drooping. | |
| C. Shoots and pedicels pubescent. | |
| D. Flowers mostly in twos. | |
| E. Fruits large, more than 1 inch in diameter, variable in
shape, often compressed; tree large; stamens about 30. | 1. P. domestica. |
| E.E. Fruit small, less than 1 inch in diameter, uniformly
oval or ovoid; stamens about 25; tree small, compact. | 2. P. insititia. |
| D.D. Flowers mostly single. | |
| E. Leaves small, less than 2 inches in length; sometimes
a tree; very thorny | 3. P. spinosa. |
| E.E. Leaves large, more than 2½ inches in length; a shrub;
thorns few | 4. P. curdica. |
| C.C. Shoots glabrous or soon becoming so, pedicels glabrous. | |
| D. Pedicels shorter than the calyx-cup; leaves glabrous or
sparsely pubescent on the under side along the rib; flowers in pairs | 5. P. cocomilia. |
| D.D. Pedicels more than twice as long as the calyx-cup. | |
| E. Flowers mostly single; leaves hairy along the midrib on
the under side; petiole ⅕ as long as the leaf-blade; a tree | 6. P. cerasifera. |
| E.E. Flowers in threes; leaves glabrous, petiole shining,
leaf-margins finely and closely serrate, teeth glandular-pointed;
stamens about 25 | 7. P. monticola. |
| E.E.E. Flowers in threes; leaves glabrous, often shining,
leaf-margins finely and closely serrate, teeth glandular-pointed;
stamens about 25 | 8. P. triflora. |
| B.B. Leaves upright, peach-like, glabrous, veins very
conspicuous, under side barbate at axils of veins; separated from
all other plums by the leaf-characters and by the large, flattened,
brick-red fruits | 9. P. simonii. |
| A.A. Flowers in clusters of 3 or more, rarely 2. American plums. | |
| B. Plants trees. (P. angustifolia rarely a tree.) | |
| C. Leaves broad, mostly ovate or obovate. | |
| D. Leaves long-ovate or long-obovate. | |
| E. Flowers white. | |
| F. Leaf-serrations glandless, acute; petiole usually
glandless; calyx-lobes entire, glabrous on the outer, pubescent on
the inner surface; stamens about 30; stone turgid, large, pointed
at the apex | 10. P. americana. |
| F.F. Leaf-serrations glandular, wavy-crenate; petioles
glandular; calyx-lobes glandular-serrate, pubescent on the inner surface;
stamens about 20; stone turgid, small, prolonged at the ends | 11. P. hortulana. |
| E.E. Flowers fading to pink. | |
| F. Leaf-serrations coarse, rounded, glandular only when
young; petioles biglandular; calyx-lobes glandular-serrate, not pubescent
on the inner surface; stamens about 30; fruit red; bloom light; stone flat | 12. P. nigra. |
| F.F. Leaf-serrations fine, acute, glandular-pointed; petioles
biglandular; calyx-lobes entire, pubescent on the outer, tomentose on the
inner surface; fruits dark purple; bloom heavy; stone turgid, acute at
the ends | 13. P. alleghaniensis. |
| D.D. Leaves round-ovate, obtusely, sometimes doubly
serrate; petioles glandless; calyx-lobes pubescent on both surfaces;
fruit dark red or purplish; stone turgid, pointed at both ends | 14. P. subcordata. |
| C.C. Leaves narrow, lanceolate-ovate. | |
| D. Leaves flat. | |
| E. Leaves glabrous; fruits globular, usually purple at
maturity but sometimes red or orange-red; bloom thin; stone turgid,
cherry-like | 15. P. umbellata. |
| E.E. Leaves pubescent. | |
| F. Stone acute at both ends; fruit purple. | 16. P. mitis. |
| F.F. Stone rounded at base; fruits variously colored | 17. P. tarda. |
| D.D. Leaves more or less folded upward. | |
| E. Fruits small, ½ inch in diameter, cherry-like;
leaves lanceolate, upper surface glabrous, lustrous, lower surface
pubescent in axils of veins, marginal teeth glandless; petioles
biglandular; stone small, ovoid, turgid, cherry-like; rarely a
tree; tender in New York | 18. P. angustifolia. |
| E.E. Fruits large, an inch in diameter, plum-like;
leaves lanceolate, peach-like, upper surface glabrous, lower
surface pubescent along the midrib; petioles with from 1 to 6
glands; stone compressed and pointed at both ends; usually a
tree; hardy in New York | 19. P. munsoniana |
| B.B. Plants shrubs. | |
| C. Fruits dark purple. | |
| D. Leaves ovate, acute, finely serrated; shoots becoming
glabrous; stones pointed at both ends | 20. P. maritima. |
| D.D. Leaves oval-orbicular, crenate-serrate; shoots
usually pubescent; stone pointed only at the base | 21. P. gravesii. |
| C.C. Fruits red or orange, sometimes yellow but never
deep purple. | |
| D. Fruits large, 1 inch in diameter; leaves oblong-ovate,
long-pointed, margin serrate with incurved sometimes glandular teeth,
upper surface glabrous, lower surface pilose; petiole with 1 or 2
glands; stone oval, flattened | 22. P. orthosepela. |
| D.D. Fruits small, ½ inch in diameter. | |
| E. Leaves small, ovate-lanceolate or oval, margins
finely and evenly serrate, upper surface glabrous, lower surface
soft pubescent; petioles short and stout; fruits variable in color,
mostly red; stone turgid, pointed at both ends | 23. P. gracilis. |
| E.E. Leaves oblong-ovate, margins coarsely or doubly
serrate, glabrous above and sparingly pubescent below; petiole
glandular; fruits cherry-red | 24. P. rivularis. |
