DIOSCORE^. 587 



The Yams are the esculent tubers of several cultivated species of Bioscorea, said to be 

 introduced formerly from Africa and Asia. 



1. DIOSCOREA, L. 



Capsule 3-celled, dehiscent at the wing-shaped angles. Seeds flat, winged ; cotyledon 

 flattish. — Stem twining, herbaceous from a tuberous root; flowers mostly diceciotis, usually 

 greenish. 



Sect. 1. Amphistbmon. — Stamens 6, all fertile, or % destitute of anthers, inserted into 

 the rotate perigone : anthers subglobose, about as long as the filament. 



* $ and $ flowers in simple spikes. 



1. D. cayeunensis, Lam. Stem cylindrical, or angular, usually prickly below ; leaves 

 mostly opposite, cordate-roundish, or deltoid, glabrous, sparingly dotted with pellucid lines, 

 9-nerved with the exterior pair united at the base ; spikes simple ; $ flowers distant : 

 anthers 6 ; capsule leathery, elliptical-oblong : seeds winged at the base. — ^D. Berteroana 

 Kth. — Tuber " compressed-globose, small ;" leaves variable, about 3" diam. 



a. $ spikes single in the axils. 



/3. rotundafa, Poir. S spikes geminate or fascicled. 



Hab. Jamaica !, March (;8) ; [French islands ! (o) ; Guiana, equat. Brazil]. 



2*. D. bulbifera, L. Stem subcylindrical, bulbilliferous ; leaves alternate, cordate- 

 ovate, cuspidate, glabrous, devoid of pellucid dots or lines, 9-nerved with the exterior pair 

 united; "spikes simple: S flowers distant: anthers 6; capsule elliptical-oblong: seeds 

 winged at the base." — Wight, le. t. 878. Desc. Fl. 8. t. 535.— Helmia, XM.— Tuber 

 " globose ;" leaves 4"-3" long, 3"-3i'' broad. — Hab. Naturalized in Antigua !, Wullsohl. ; 

 [cultivated, introduced from East Indies]. 



** S flowers in whorled-compound, $ in simple spikes. 



3*. D. alata, L. Stem 4-winged, (or angular) ; leaves opposite, cordate-oblong, or 

 cordate-ovate with a spreading, basUar sinus, glabrous, devoid of pellucid lines, 7(-9)-nerved 

 with the exterior pair united ; S spikes compound ; special ones whorled-fascicled, short, 

 flexuose : flowers distant : anthers 6 ; capsule leathery, elliptical : seeds surrounded by a 

 wing.— Wight, Ic. t. 810. Desc. Fl. 8. t. 537.— Tuber large. From the descriptions of 

 former authors it is still doubtful wbether there ai-e not several species comprised under the 

 following forms : 



o. Stem 4-winged; "tuber simple" {SI. p. 139, Roaib., Wight.) 



P vulgaris, Miq. " Stem 4-gonal; tnber palmatifid,"— 2^j«. Fl. 2. t. 28. 



y. (?) altissima. Lam. " Stem cylindrical {SI. p. 140, W.); taber palmatifid" {SI.) Plum.. 



Ed. Burm. t. 117./ 2. 



Hab. Cultivated and naturalized in Jamaica, [Haiti !, Portorico !, and French islands !(o), 



said to be introduced] . 



*** S flowers racemose, 9 in compound spikes. 

 4*. D. triphylla, L., Jacq. Stem subcylindrical ; leaves opposite, or " alternate," 3- 

 folioiate ': leaflets petiolulate, ovate, pointleted, glabrous, subcordate, or oblique at the base, 

 S-nerved • S flowers in simple or simply branched racemes : " 3 stamens fertile ; ? spikes 

 simply branched; capsule chartaceous, elliptical: seeds " winged at the base {Jm-\— 

 Jacq'ic. Rar. t. 627.-Tuber "globose;" leaflets 3" long, 2" broad ; capsule 12"'^14"' 

 long, 10'" broad.— Hab. Naturalized in Jamaica !, March, [said to be introdncedj. 



Sect 2 Efisi^uom.— Stamens 6, all fertile, inserted into the infundibular pengone : 

 anthers adnate, much shorter than the fllament.—ljRs.ves alternate, 



5* D trifida, L. Stem angular, narrowly winged; leaves S-5-loied hejoni the 

 middle, glabrous ('or glabrate beneath), dotted with pellucid lines : middle lobe Z-nerved, 

 ovate-oblong, or oblong-lanceolate, acuminate, lateral semicoi-date or 2-lobcd at the base; 

 3' .flowers in slender, simple racemes, ? in spikes : rhachis hairy.-Leaves 6' -3" d.am.. 



