430 
** Flowers in pairs from the axils of the bracts, densely spicate. 
4, A. heteracantha Zuce. Subcaulescent (1 to 1.5 em. high): seape 18 to 30 dm, 
high: leaves thick, rigid, linear-lanceolate (3 to 5 dm, long), with hooked spread- 
ing teeth, the terminal spine subterete, unarmed below: bracts lanceolate, from a 
clasping base; flowers subsessile: perianth longer than the oblong ovary; lobes 
linear-oblong, erect, much longer than the very short campanulate tube: pod ovate 
or oblong, more or less cuspidate.—Very common on most of the limestone high- 
lands of southwestern Texas. 
** * Flowers paniculate toward the apex of the branches. 
5. A. Parryi Engelm. <Acaulescent: leaves ascending, scarcely narrowed above 
the dilated base, ovate-lanceolate (25 to 30cm. long), strongly attenuate at apex and 
terminating in a robust flattened spine (2.5 cm. long), with small marginal teeth: 
scape (24 to 36 dm. high) strongly imbricated with large foliaceous triangular 
bracts, bearing a large panicle (6 to 9 dm. long) with spreading branches: flowers 
very numerous, over 5 em. long, yellowish-white, the tube funnelform and twice 
shorter than the oblong-linear lobes: stamens adnate to the top of the tube, long- 
exserted, equaling the style: pod ovate, very short cuspidate, with flat punctate 
large seeds.—From the mountains below El Paso to western New Mexico. 
6, A. rigida Mill, Caulescent, 3 to 6 dm. high: leaves lanceolate-linear (4 to 6 
dm. long), contracted above the broader base, glaucescent, toothed, the terminal 
spine thick (2.5 em, long), the marginal scattered and mostly straight: seape (36 
todidm. high) with broad foliaceous bracts, and horizontally branched panicle with 
pale yellowish-green paniculate flowers, the tube shorter than the lobes: stamens 
inserted about the middle of the tube, blood-red above, long-exserted, equaling the 
style.—Woods below Ringgold. 
7. A. Wislizeni Engelm. Acauleseent: leaves ovate (3 dm, long), narrowed 
above the base, broader above the middle, acute, the spines subflexuous, blackish, 
decurrent, the terminal 20 to 22 mm. long, stout, the marginal rigid, the upper 
larger and straight, the lower smaller and subdetlexed: scape 36 dm. high, with a 
loosely-tlowered panicle: ovary equaling the lobes and tube of the perianth: sta- 
mens long-exserted, adnate to the middle of the tube: pod slender, prismatic, 
acute.—Gaudalupe and Chisos mountains. 
DIOSCOREACEHR. (YAM Famty.) 
Plants with twining stems from a large tuberous or knotted root- 
stock, ribbed net-veined petioled leaves, small diccious 6-androus 
regular flowers, the 6-cleft calyx-like perianth adherent in the fertile 
plant to the 3-celled ovary, and 3 distinet styles. 
1. DIOSCOREA L. (Yam.) 
Herbaceous plant, with very small flowers in axillary panicles or 
racemes, stamens at the base of the parted perianth, the 3-winged 
3-celled pod loculicidally 3-valved by splitting through the winged 
angles, and 1 or 2 flat seeds (with a membranaceous wing) in each cell. 
1. D. villosa L. (WiILp YAM.) Stems slender, from a matted rootstock, climbing 
over bushes: leaves mostly alternate, sometimes nearly opposite or in 4s, more or 
less downy beneath, cordate, conspicuously pointed, 9 or 11-ribbed: flowers pale 
greenish yellow, the sterile in drooping panicles, the fertile in drooping racemes: 
pod 16 to 20 mm. long.—Extending into Texas from the Atlantic States. 
