662 Bulletin 320 



and the style is flattened laterally and bearded down the inner edge, 

 while in Lathyrus the style is flattened on the back and front and is 

 bearded down one face. 



The flowers of Lathyrus are solitary or racemose, on long, axillary 

 peduncles. The calyx is oblique, campanulate, five-parted, the teeth 

 nearly equal or the upper two shorter than the lower. The corolla con- 

 sists of five parts. The upper, or odd, petal, known as the vexillum, or 

 standard, is larger than the others and encloses them in the bud. There 

 is a notch at the apex and ordinarily a short claw. The form is broadly 

 obovate or roundish and the petal is usually turned backward or spreading. 

 The colors are dark blue or purple, violet, rose, white, or yellow. The 

 two lateral petals, or wings, are falcate, obovate, or oblong, oblique and 

 exterior to the lower two, which are shorter, incurved, connivent, and 

 more or less coherent along their anterior edge, forming the keel, or carina. 

 The keel encloses the stamens and pistil. 



The stamens are diadelphous (9 and i), or monodelphous below. The 

 style is curved, sometimes twisted, flattened, hairy along the inner side 

 (next the free stamen) ; ovary sessile, or stalked with numerous ovules, 

 becoming a one-celled pod. This is flat or terete, dehiscent, two-valved, 

 continuous between seeds. 



The seeds are globose or angular, with a hard, smooth testa. The 

 radicle is curved inward. The cotyledons are accumbent. 



The plants are herbaceous vines, rarely erect herbs, with pinnate, 

 mostly tendril-bearing leaves. The old genus Orobus, which originally 

 was created to include all the erect forms without tendrils, has since been 

 included in the genus Lathyrus by Bentham and Hooker and by later 

 botanists. 



Species of Lathyrus are found in Europe, Asia, northern Africa, Sicily, 

 and North and South America. 



The genus is generally divided into two sections: 



1. Eulathyrus (from eu, well, and lathyrus; genuine species). Vexillum 



toothless at the base. Leaves opposite or wanting. Petioles 

 narrow- winged . 



2. Clymenum (dymenos, clear). Vexillum furnished with a conical 



gibbosity on each side at the base. Lower petioles leafless; upper 

 ones bearing two to six usually alternate leaflets. Petioles usually 

 winged. 



Horticulttirally the species may be divided into perennial and annual 

 species. The following classification of the species is based in part on the 

 artificial key to the American species, published by Theodore G. White 

 in the Bulletin of the Torrey Botanical Club, Vol. XXI, 1894: 



