HOW TO KNOW THE GRASSES 



12b. Spikelets dorsally compressed, awnless; hairs white. Fig. 293. 



COTTONTOP Trichachne caWoTnica (Benth.) Chase 



Perennial; tufted, from knotty stooling 

 crowns; plants 30 — 100 cm. tall, with rather 

 dense, slender panicles 5 — 10 cm. long. The 

 panicles have a silvery white color, rarely 

 tinged with purple when young; spikelets 

 with a minute first glume; second glume 

 shorter and narrower than the fertile lem- 

 ma. Cottontop furnishes good summer and 

 winter feed in the Southwest, but is grazed 

 mostly just after rains, when it makes rapid 

 growth. Rocky ridges, margins of fields, 

 in brush. August— October. 



13a. Spikelet without a cup or ring at the base; first glume present 

 or absent 14 



13b. Spikelet with a cup- or ring-like swelling at the base, without an 

 evident first glume. Fig. 294. 



PRAIRIE CUP GRASS rriocWoa contracta Hitch. 



Annual; tufted; culms sometimes de- 

 cumbent; plants 30 — 70 cm. tall. The 

 panicles are slender, made up of nearly 

 erect racemes. The cup-Hke swelling at 

 the base of the spikelet is a modified 

 first glume. The fertile floret is some- 

 what shorter than the sterile lemma and 

 bears a short, hairy awn which is con- 

 cealed within the spikelet. Open ground, 

 moist places, ditches. June — October. 

 There are seven other species of this 

 genus, all rather similar, in the southern 

 states. 



Figure 294 



14a. Glumes or sterile lemma awned (the own sometimes reduced to 

 an abrupt point) 15 



14b. Glumes and sterUe lemma awnless. 



16 



155 



