18 CONTKIBUTIONS FKOM THE NATIONAL HEEBAEIUM. 



degree of difference between this and any other species of the group 

 is much greater than that between such species as P. fasciculatum, 

 P. arizonicum, and P. adspersum. But other groups, such as the 

 Lanuginosa, are made up of closely allied species, connected with one 

 another by intergrades, to form a composite taxonomic network whose 

 component parts cannot be definitely distinguished by clean-cut 

 lines of demarcation. 



DESCRIPTION OF THE GENUS AND SPECIES. 

 PANICUM L. 



Panicum L. Sp. PI. 55. 1753. 

 Sttinckisma Raf. Bull. Bot. Seringe 220. 1830 fl 

 Phanopyrum (Raf.) Nash iu Small, Fl. Southeast. U. S. 104. 1903.& 

 Spikelets articulated below the glumes, falling entire, more or less compressed 

 dorsoventrally, arranged in panicles, rarely in racemes; glumes two, herbaceous, 

 nerved, usually very unequal, the first often minute, the second typically equaling 

 the sterile lemma, the latter of the same texture and simulating a third glume, bearing 

 in its axil a membranaceous or hyaline palea and sometimes a staminate flower, the 

 palea rarely wanting; fertile lemma chartaceous-indurated, typically obtuse, the nerves 

 obsolete, the margins inrolled over an inclosed palea of the same texture, a lunate 

 line of thinner texture at the back just above the base, the radicle protruding through 

 this at germination; stamens three, styles two, stigmas plumose; grain dorsoventrally 

 compressed, with a punctiform hilum, free within the firmly closed lemma and palea. 

 Annual or perennial herbaceous grasses, of various habit, confined to the warmer 

 regions of both hemispheres. 



A number of species here included in the genus Panicum depart in some measure 

 from these generic characters. The subgenus Paurochaetium approaches Chaetoehloa 

 Scribn. and the group hitherto referred to Panicum section Ptychophyllum A. Br., in 

 that the uppermost spikelet of each branchlet is subtended by a bristle-like prolonga- 

 tion of the axis. Panicum geminatum Forsk. and P. paludivagum Hitchc. & Chase 

 have a racemose inflorescence as in Brachiaria Griseb., but the spikelets are placed 

 with the back of the fruit turned toward the rachis as in true Panicum, not in the 

 reverse position as in Brachiaria. In P. barbinode Trim, P. arizonicum Scribn. & Merr., 

 and P. texanum Buckl. spikelets toward the ends of the branches are often placed in 

 the reverse position characteristic of Brachiaria, while others on the same branch are 

 placed with the back of the fruit toward the axis, showing that in an inflorescence 

 not strictly racemose this character of the position of the spikelets in relation to the 

 axis is not of taxonomic significance, since it depends on whether one or the other of a 

 pair of spikelets on a one-flowered branchlet has been developed. Hence this charac- 

 ter, while distinguishing between Paspalum L. on the one hand and Axonopus Beauv. 

 and Brachiaria Griseb. on the other, does not alone clearly separate the latter from 

 Panicum^ but must be taken in connection with the strictly racemose inflorescence. 

 In Panicum elephantipes Nees the thin but not hyaline margins of the acuminate lemma 

 are not inrolled above the middle, the fruit thus suggesting an approach to Valota 

 Adans. , but in texture it is not cartilaginous and papillose as in that genus nor does 

 P. elephantipes approach Valota in habit or inflorescence. In the Verrucosa and the 

 related Trichoidia the firm-margined lemmas are not inrolled except at the base. 



a See discussion under P. Mans, p. 118. 



&See discussion under P. gymnocarpon, p, 327. 



