36 Bulletin VIL 1. 



9. PANIOUM Linn. Sp. PI. 55 (1753). 



Spikelets one-flowered or sometimes with a staminate flower be- 

 low the hermaphrodite terminal one, in spikes, racemes, or pani- 

 cles, rachilla articulated below the empty glumes. Glumes four, 

 the first usually much shorter than the others, very rarely want- 

 ing; second glume empty, equalling or somewhat shorter than the 

 third, which is empty or has a palea or even a staminate flower in 

 its axil; fourth glume smooth and shining, coriaceous, much firmer 

 in texture than the others. Palea similar in texture to its glume 

 and closely embraced by it. Grain enclosed within the hardened 

 fruiting glume and palea, free. 



Annuals or perennials varying greatly in habit of growth, foli- 

 age, and inflorescence. Species about three hundred, throughout 

 the tropical and subtropical regions of both hemispheres; a few 

 only in the temperate regions. Several species occur as weeds 

 throughout the civilized world. Nearly ninety species and varie- 

 ties are recorded as having been observed in Tennessee. The spe- 

 cies are difficult to identify, especially those in the group contain- 

 ing Panicum dichotomum^ owing to the variations in habit which 

 the several species present at different periods of growth, and 

 the fact that a number of the older published descriptions were 

 based wholly upon one or the other of these stages. In recent 

 published manuals there is very little to aid one in the identification 

 of these species. Aside from this group, which can never be satis- 

 factorily discriminated until the types in European herbaria are 

 consulted, our species are very well marked. 



KEY TO THE SPECIES. 



I. Spikelets in one-sided, usually simple racemes 2 



1. Spikelets variously paniculate 6 



2. Racemes slender, digitate or sub-fasciculate, outer glumes 



softly pubescent or pilose 3 



2. Racemes thick and racemed along the main axis, or somewhat 



paniculate, outer glumes rough 5 



3. Second glume narrow, about one-half as long as the spikelet 



I. P. SANGUINALE. 



3. Second and third glumes nearly equal 4 



4. Sheaths and leaves glabrous, racemes spreading, spikelets 



about one line long 2. P. glabrum. 



4. Sheaths pilose, racemes filiform, erect or ascending, spikelets 



about three-fourths of a line long . . . 3. P. filiforme. 



5. Racemes of unequal length, erect or ascending, approximate, 



the upper crowded; second and third glumes awned or 

 awn-pointed 4- ?• crus-galll 



5. Racemes nearly equal, spreading rather distant; second and 



third glumes acute or mucronate-pointed. 5. P. colonum. 



6. Spikelets crowded in narrow almost spike-like panicles, the 



second glume twice as long as the fourth, and gibbous at 

 the base 6. P. gibbum. 



