■40 KEY TO THE SPECIES 



1. Crataegus rivularis Nutt. (Riverside Thorn). Spines few, stout, 3-4 cm. 

 long ; leaves ovate, serrate, mostly acute at apex and cuneate at base, pubescent 

 or nearly glabrous ; corymbs 5-8 flowered, the petals white ; fruit black, 10-14 mm. 

 in diameter. Frequent on stream banks. 



XXXI. DRUPACEiE (Plum Famlt) 



Trees or shrubs with the characters of Rosacem^ but with 

 simple leaves, a single style, and a superior l-celled ovary 

 becoming a fleshy fruit with a stone {drupe), 



1. PRUNUS (Plum. Peach. Cherry) 



Small trees or shrubs with clusters of flowers, a bell-shaped to tubular 5-cleft 

 calyx, 5 spreading petals, and 15-20 stamens. 



1. Prunus demissa melanocarpa Aven Nelson (Eocky Mountain Choke- 

 cherry). Generally a small shrub 1-3 m. high, sometimes tree-like ; leaves ovate 

 or obovate, abruptly acuminate or merely acute, glabrous or slightly pubescent ; 

 the white flowers in dense racemes terminating the branchlets ; fruit large (7-9 

 mm. in diameter), black when mature, juicy and scarcely astringent. Common ; 

 moist canons and slopes. 



2. Prunus americana Marsh (Common Wild Plum). A thorny shrub or small 

 tree, 2-5 m. high ; leaves ovate, conspicuously pointed, coarsely serrate, smooth 

 when mature \ flowers usually white ; fruit roundish oval, yellow, orange, or red. 

 Woods and river banks. 



XXXII. PAPILIONACEiE (Pulse Family) 



Herbs, shrubs, or trees with alternate and usually compound 

 leaves, irregular flowers, 5 sepals more or less united, 5 very- 

 dissimilar petals (upper petal or standard larger than the 

 others and inclosing them in the bud, turned back or spread- 

 ing ; the two lateral petals or iinngs oblique ; the two lower 

 petals coherent by their edges and forming the heel which 

 usually incloses the stamens and pistil), usually 10 variously 

 united stamens (mostly 9 united into a tube and the upper one 

 separate), and a 1-celled ovary becoming a more or less elon- 

 gated pod. (See Plant Structures, p. 264, Fig. 250.) 



* LeaTes trifoliate ; stamens 10, distinct ; pods long. 



1. Thermopsis. Stipules conspicuous ; flowers yellow, in racemes. 



* * Leaves digitately 6-11 foliate ; stamens 10, monadelphous ; pods large. 



2. Iiuplnus. Calyx 2-lipped ; anthers of 2 forms. 



* ♦ * Leaves trifoliate ; stamens 10, diadelphous ; anthers all alike ; pods 

 Bmall. 



3 Medicago. Flowers in racemes ; pods curved or coiled. 



4. Melilotus. Flowers in racemes ; pods with thick wrinkled walls. 



