DRUPACEiE 397 



the stone ("pit") of the plum consists of hardened endocarp, 

 seed coat, and embryo. The stone is compressed. 



Classification of Plums.- — For a complete description of the 

 species of plums in American plum culture, see "The Plums 

 of New York"; Hedrick, Report of the N. Y. Agr. Exp. Sta., 

 vol. 3, pt. II, 1911; and Wight, W. F., "Native American 

 Species of Prunus," Bull. 179, B. P. I., 1915. 



Key to Principal Species of Pltjms * 



Flowers in clusters of one or two (three in P. Iriflora), Old World Plums. 

 Shoots and pedicels pubescent. 



Fruits large, more than i inch in diameter, variable in shape, often 



compressed; tree large; stamens about 30, P. domestica. 

 Fruits small, less than i inch in diameter, uniformly oval or ovoid; 

 tree small, compact; stamens about 25, P. insUitia. 

 Shoots glabrous or soon becoming so, pedicels glabrous. 

 Flowers mostly single, P. cerasifera. 

 Flowers in threes, P. Iriflora. 

 Flowers in clusters of three or more, rarely two, American Plums. 

 Leaf serrations glandless, acute; calyx lobes entire, glabrous on the outer, 



pubescent on the inner surface, not glandular, P. americana. 

 Leaf serrations glandular (at least when they first unfold), rounded or ob- 

 tuse; calyx lobes glandular (except in P. angustifolia). 

 Leaves broad, mostly oblong-ovate or obovate, the margin often doubly 

 serrate; flowers 2 to 2.5 centimeters broad; calyx with a reddish 

 tinge, at least when old, the lobes glandular serrate, P. riigra. 

 Leaves narrow, ovate, ovate-lanceolate, the margin rarely doubly serrate; 

 flowers 8 to 15 millimeters broad; calyx rarely reddish, the lobes entire, 

 either glandular or glandless. 

 Leaves thick, slightly lustrous on upper surface; veins conspicuous below; 



margin coarsely and irregularly serrate, P. horlulana. 

 Leaves usually thin, lustrous on upper surface, veins not conspicuous 

 below, margin finely and evenly serrate. 

 Leaves usually 6 to 10 centimeters long; calyx lobes glandular, P. 



munsoniana. 

 Leaves 2 to 6 centimeters long; calyx lobes glandless, P. angustifolia. 



* Adapted from The Plums of New York by Hedrick. 



