HITCHCOCK AND CHASE NORTH AMEEICAN PANICUM. 



209 



Autumnal form ascending or spreading, 



branching from middle and upper 



nodes; the reduced, fascicled blades 



strongly ciliate. 



Culms 40 to 70 cm. high, autumnal 



culms usually 40 to 50 cm. long; 



southeastern U. S 126. P. lanuginosum. 



Culms 20 to 40 cm. high, autumnal 

 culms usually 20 to 30 cm. long, 

 the early branches zigzag; West 



Indies 127. P. acuminatum. 



Plants pubescent, often villous, but not velvety. 



Culms conspicuously pilose with long, horizontally 

 spreading hairs; branching before expansion of 



primary panicles 131. P., praecocius. 



Culms variously pubescent, if pilose the hairs not 



long and horizontally spreading. 



Vernal blades glabrous or nearly so on the upper 



surface, firm in texture. 



Autumnal culms branching from the lower 



nodes, forming a spreading bunch 10 



to 15 cm. high; Pacific slope 133. P. ocddentale. 



Autumnal culms branching from the middle 

 nodes, forming widely spreading mats; 

 Atlantic slope (see also form of P. hua- 



chucae silvicola) 125. P. tennesseense. 



Vernal blades pubescent on upper surface, some- 

 times pilose near base and margins only. 

 Spikelets 1.3 to 1.5 mm. long; vernal blades 

 long-pilose on upper surface. 

 Autumnal form widely decumbent- 

 W spreading, forming a mat; vernal 



culms soon geniculate-spreading ; 



plants olivaceous 122. P. albemarlense. 



Autumnal form erect or leaning, never 

 forming a mat; plants yellowish- 

 green. 

 Axis of panicle pilose, panicle '^ I 



: branches tangled, the lower 



drooping/.". . . .^.^ .,. 123. P. impUcatum. 



Axis of panicle"^ puberulent only, 

 panicle branches not tangled, 



the lower ascending^. 121. P. meridionale. 



Spikelets 1.6 to 2 mm. long; vernal blades 

 pilose or pubescent. 

 Upper surface of blades pilose; spike- 

 lets 1.8 to 2 mm. long; autumnal 

 form decumbent-spreading. 

 Spikelets pointed; culms weak and 



lax 136. P. languidum. 



Spikelets obtuse; culms not weak 

 and lax. 



41616°— VOL 15—10 14 



