POACEAE 143 
6. Tridens Drummóndii (Scribn. & Kearn.) Nash. Stems 8-12 dm. tall from a 
scaly rootstock, smooth : basal leaf-sheaths crowded, villous, the upper ones glabrous or 
nearly so; blades of the basal leaves elongated, 2-4 dm. long, about 5 mm. wide ; blade 
of the uppermost stem-leaf 3 cm. long or less: panicle narrow, spike-like, 1.5-2 dm. long, 
its branches short and appressed : spikelets rather loosely arranged, 3-5-flowered, 8-10 
mm. long; empty scales broad, 1-nerved, short-awned at the shortly 2-toothed apex; 
flowering scales firm, 5-6 mm. long, elliptic-ovate when spread out, their nerve-hairs about 
0.8 mm. long, the apex 2-lobed, the nerves excurrent as projections.  [ Z'riodia Drummondii 
Scribn. & Kearn.] 
In dry soil or in low pine lands, South Carolina to Mississippi and Florida. Fall. 
7. Tridens strictus ( Nutt.) Nash. Stems5-15 dm. tall, smooth : leaf-sheaths smooth ; 
blades erect or ascending, 4 dm. long or less, 2-7 mm. wide, long-acuminate, smooth ex- 
cept on the margins: panicle narrow, spike-like, 1.5-3 dm. long, 1-1.5 em. broad, its 
branches short and appressed : spikelets crowded, 6-10-flowered, 5-6 mm. long ; empty 
scales narrow, l-nerved, acuminate, usually exceeding the flowering scales; flowering 
scales 3.5—4 mm. long, 1.5 mm. broad and elliptic when spread out, their nerve-hairs about 
0.8 mm. long, the lateral nerves usually slightly excurrent, the midnerve extended into a 
short awn 0.25-0.5 mm. long. ['iodia stricta ( Nutt. ) Vasey.] 
In moist soil and meadows, Kansas to Mississippi and Texas. Summer and fall. 
8. Tridevs congéstus (L. H. Dewey) Nash. Stems tufted, 1-7 dm. tall, smooth : 
leaf-sheaths shorter than the internodes, smooth ; blades ascending, 5-20 cm. long, 2-5 
mm. wide, long-acuminate, smooth beneath, roughish above: panicle dense, 3-8 cm. long, 
1-1.5 em. broad, its branches short and erect: spikelets nearly sessile, crowded, turgid, 
8-15-flowered, 8-12 mm. long, about 4 mm. broad, ovate to oblong ; empty scales broad, 
l-nerved, acute ; flowering scales about 5 mm. long, orbicular when spread out, their nerve- 
hairs about 0.8 mm. long, the midnerve and often also the lateral nerves excurrent in short 
projections; palet-nerves hispid and saccate at the base. [Triodia congesta L. H. Dewey.] 
In dry soil, Texas. Spring to fall. 
9. Tridens müticus (Torr.) Nash. Stems tufted, 2-5 dm. tall, roughened: leaf- 
sheaths glabrous or papillose-hirsute ; blades erect or ascending, 2-12 cm. long, 3 mm. 
wide or less, often involute when dry, rough : panicle narrow, 6-15 cm. long, its branches 
appressed : spikelets 6-9-flowered, 10-12 mm. long, lanceolate ; empty scales l-nerved ; 
flowering scales 4-5 mm. long, obscurely and irregularly lobed at the obtuse or rounded 
apex, the hairs on their margins and midnerve about 1.5 mm. long, the lateral nerves 
vanishing below the apex, the midnerve also, or the latter continued to the apex, or rarely 
excurrent as a short projection.  ( T'rieuspis mutica Torr. ] 
On dry hills, Texas to Arizona and northern Mexico. Spring to fall. 
10. Tridens elongàtus (Buckl.) Nash. Stems tufted, 3-9 dm. tall, very rough : leaf- 
sheaths longer than the internodes, rough ; blades erect or ascending, 4-25 cm. long, 3 mm. 
broad or less, long-acuminate, rough: panicle narrow, 12-25 em. long, its branches ap- 
pressed : spikelets 8-10-flowered, 10-14 mm. long, 3-4 mm. wide, elliptic; first empty 
scale 1-nerved, the second 3-5-nerved ; flowering scales 5-6 mm. long, the apex obtuse or 
minutely 2-toothed, their hairs on the margins and midnerve about 1 mm. long, the lateral 
nerves vanishing below the apex, the midnerve excurrent as a short projection. 
On plains or prairies, Colorado to Texas and Arizona. Summer and fall. 
11. Tridens Buckleyànus (Vasey) Nash. Stems 6-8 dm. tall, very rough, as are 
the sheaths: leaf-blades 0.5-2 dm. long, 1-2.5 mm. wide, involute when dry, rough on 
both surfaces: panicle narrow, slender, 1.5-2.5 dm. long, its main axis and appressed 
branches rough, the larger ones 3-5 em. long : spikelets loosely disposed, 3-5-flowered, 5-8 
mm. long, 1.5-2 mm. wide, narrowly elliptic ; empty scales narrow, acuminate, the first 
1-nerved, the second 3-nerved ; flowering scales about 5 mm. long, elliptic and about 2 mm. 
wide when spread out, the apex minutely 2-toothed, the midnerve sometimes excurrent in 
a short tip between the teeth, the lateral nerves vanishing just below the apex, the hairs on 
the margins and midnerve scanty, about 0.4 mm. long. [Triodia Buckleyana Vasey. ] 
In dry soil, southern Texas. Summer and fall. 
98. ERIONEURON Nash. 
Perennial tufted grasses, with thick linear leaf-blades having thickened white mar- 
gins, and dense contracted almost capitate panicles. Spikelets several-many-flowered : 
empty basal scales 2, narrow, acuminate : flowering scales broad, 3-nerved, pubescent on 
the nerves below, and sometimes also on the body of the scale at the base, with long silky 
