GRAMINEAE (GRASS FAMILY) 



155 



Annuals. 



Florets not webby at the base ; lemmas distinctly 5-nervetl . . 

 Florets webby at the base; intermediate pair of nerves obscure . 

 Pert-n nials. 

 Culms from extensively creeping rootstocks, not tufted. 



Culms flattened ; spikelets not over 6 mm. long 



Culms terete; spikelets 8 mm. or more long 



Culms tufted. 

 Creeping rootstocks present. 



1'aniclc cruwiled ; culms much exceeding the leaves . . . 

 Panicle diffuse ; culms scarcely exceeding the basal leaves 

 No creeping rootstocks, but culms sometimes decumbent at base. 



Lemma glabrous 



Lemma pubescent at least on the keel. 



Culms upright from a stout crown or caudex ; leaves short and flat 

 Culms from a more slender base forming loose tufts, often decum- 

 bent. 



Culms rarely over 8 dm. high, with lax leaves, the decumbent 

 bases of the culms forming loose tufts ; lemma pubescent 

 but very sparsely webbed ; alpine or northern plants . 

 Culms taller, or if low, stiff and with scarcely decumbent bases. 

 Lemma not webbed at base. 



Panicle narrow; lemma glabrous between the nerves below 

 Panicle spreading ; lemma pubescent between the nerves 



below 



Lemma webbed at base. 

 Marginal nerves glabrous. 



Lemma prominently nerved ; sheaths scabrous . . . 

 Lemma obscurely nerved ; sheaths smooth ... 

 Marginal nerves pubescent. 



Intermediate nerves of lemma obscure ; florets acute. 

 Panicle erect, 0.41 dm. long (rarely longer), branches 



ascending 



Panicle drooping, 1-8 dm. long, branches spreading 

 Intermediate nerves of lemma prominent ; florets obtuse 



or acutish. 

 Branches of panicle spikelet-bearing from the middle ; 



spikelets 34 mm. long 



Branches of panicle elongated, spikelet-bearing only at 

 the ends ; spikelets 5-6 mm. long .... 



1. P. annua. 



8. P. Chapmaniana. 



8. P. comprtMa. 

 4. /'. eminent. 



10. P. pratentig. 



17. P. urachyphylla. 



18. P. debilis. 

 6. /'. ii/jiina. 



6. P. laxa. 



7. P. glauca. 



16. P. autumnalis. 



11. P. triviaUs. 

 14. P. aluodes 



8. P. nemoralit. 



9. P. triflora. 



12. P. sylvestrte. 

 15. P. Wolfli. 



* Annuals, rarely over 2.6 dm. high, tufted. 



1. P. ANNUA L. (Low SPKAR GRASS.) Culms flattened, decumbent at base, 

 sometimes rooting at the lower nodes ; sheaths loose; leaves very soft; panicle 

 pyramidal, 3-8 cm. long, rarely longer; spikelets crowded, 3-6-flowered, about 

 4 mm. long; lemma distinctly b-nerved, the nerves hairy below. Cultivated and 

 waste grounds, everywhere. Apr. -Oct. (Nat. from Eu.) 



2. P. Chapmaniana Scribn. Similar to the preceding but more strict in 

 habit ; culms terete, erect ; sheaths close, mostly at the base ; panicle more 

 oblong; florets webbed at the base, the intermediate nerves of lemmas very 

 obscure, the middle and marginal nerves sometimes hairy below. Dry soil, 

 Va. to s. 111., .and southw. Apr., May. 



* * Perennials. 

 *- Culms from extensively creeping rootstocks, not tufted. 



3. P. coMFRissA L. (CANADA BI.VE GRASS. WIRE 

 GRASS.) Bluish-green, 2-6 dm. high; culms geniculate- 

 ascending, wiry, flattened; panicles 2-8 cm. long, narrow, 

 the usually short branches in pairs, spikelet-bearing to the 

 base ; spikelets crowded, subsessile, 3-6 (rarely 9) -flowered, 

 4-6 mm. long ; lemmas obscurely nerved, more or less bronzed 

 at the summit. Dry mostly sterile soil, Nfd. to S. C., and 

 westw. ; also cultivated as a pasture grass. May-Sept. (Nat. 

 from Eu. ) FIG. 163. 



4. P. Iminens J. S. Presl. Glaucous, glabrous, 3-9 dm. 

 high ; culms stout, erect, terete ; sheaths overlapping, clus- 

 tered on the sterile shoots; blades thick, 3-8 mm. wide; p an | c i e x V 4 . 

 panide henry. -&-W cm. long, contracted ; spikelets 3-5-flow- spikeU-t and floret x 2. 

 ered, 8-12 mm. long; lemmas 4-6 mm. long, distinctly Lemma x 8. 



168. P. compressa. 



