66 Bulletin VII. 1. 



lines long", nearly equal, acute, alittle longer than the floral glume. 

 Callus of the floral glume slightly curved, very acute, barbate with 

 brown hairs, the glume scabrous near the apex, where it is mi- 

 nutely hairy. Awn scabrous, one and one-half to two and one-half 

 inches long, twisted below and usually twice bent. 



Dry ridges and hill-sides, usually in open woods. Common, grow- 

 ing in isolated tufts. April — June. 



20. MUHLENBERGIA Schreb. Gen. 44 (1789)- 



Spikelets one-flowered, hermaphrodite, variously paniculate, ra- 

 chilla articulated above the empty glumes, forming a very short 

 and usually hairy callus below the floral glume, but not extend- 

 ing above it. Glumes three, the first two empty, membranaceous- 

 or hyaline, one- to three-nerved or nerveless, usually unequal and 

 shorter than the floral glume, acute, mucronate-pointed, or some- 

 times awned; third or flowering glume narrow, smooth or more or 

 less pilose below, three- to five-nerved, awned from the acute apex 

 or from between the teeth of the more or less conspicuously biden- 

 tate apex. Awn straight or flexuose. Palea thin, two-nerved, 

 usually about the length of its glume. Stamens three. Styles 

 distinct. Grain closely enveloped by the fruiting glume. 



Perennial grasses (rarely annual) with small spikelets and greatly 

 varying habit; culms a few inches to several feet high, simple or 

 much-branched; leaves long or short, flat or strongly involute; 

 panicle narrow and spike-like or open and widely spreading. For- 

 merly included in A^rostis. 



Species about sixty, nearly all American; most abundant in 

 Mexico. 



KEY TO THE SPECIES. 



I. Culms simple, leaves convolute, panicle with widely spread- 

 ing capillary branches M. capillaris. 



1. Culms branching, leaves flat, panicle contracted 2 



2. Empty glumes minute, the lower nearly obsolete . . . 



2. M. DIFFUSA. 



2. Empty glumes one-half as long as or equalling the flower- 



ing glume 3 



3. Flowering glume awnless or simply mucronate-pointed . . 4 



3. Flowering glume conspicuously awned 5 



4. Culms nearly simple, panicle filiform, empty glumes one- 



third shorter than the flowering glume 3. M. sobolifera. 



4. Culms much branched, panicle densely flowered, empty 



glumes, at least the second, as long as the flowering 

 glume 4. M. Mexicana. 



5. Empty glumes usually bristle-pointed, as long as the flower- 



ing glume; culms much branched, panicle linear or nar- 

 row-lanceolate 5. M. SVLVATICA. 



5. Empt}' glumes acuminate-pointed, shorter than the flower- 

 ing glume; culms nearly simple, panicle elongated, very 

 slender and loosely flowered ... 6. M. Willdenovii. 



