GRAMINEAE (GRASS FAMILY) 95 



5. SORGHASTRUM Nash 



Spikelets sessile at each joint of the slender rhachis of the peduncled racemes, 

 which are reduced to 2 or 3 joints, the sterile spikelets reduced (in our species) 

 to hairy pedicels; glumes indurated as in Andropogon; sterile lemma thinly 

 hyaline, the fertile lemma reduced to hyaline appendages to the strong awn ; 

 palea obsolete. Perennial grasses with tall stout culms, the racemes arranged in 

 open panicles. (Named from its resemblance to Sorghum.) 



\. S. nutans (L.) Nash. (INDIAN GRASS, WOOD GRASS.) Culm simple, 

 1-2 m. high ; leaves 6-10 mm. wide, scabrous, glaucous ; sheaths 

 smooth ; panicle narrowly oblong, at first open, contracted after 

 flowering, 1-3 dm. long ; the spikelets lanceolate, at length 

 drooping, yellowish or reddish brown and shining, clothed, 

 especially toward the base, with fawn-colored hairs ; the 

 twisted awn longer than the spikelet. {Andropogon L. ; Chryso- 

 pogon Benth.) Dry soil, Me. to Man., and south w. FIG. 53. 



SORGHUM HALEPENSE (L.) Pers., JOHNSON GRASS, a more 

 robust plant, is found as an escape or a weed, chiefly along 

 the southern border of our range. It differs from Sorghastrum 

 in having two pediceled spikelets (of the group of three) stami- 53 g nutans x 2 

 nate or empty ; and in having a more spreading panicle and a 

 firmer lemma. This is thought by some to be the original of the cultivated 

 sorghums. (Introd. from Eu.) 



6. DIGITARIA Scop. FINGER GRASS 



Spikelets 1-flowered, lanceolate-elliptic, sessile or short-pediceled, solitary 

 or in 2's or 3's, in two rows on one side of a continuous narrow or winged 

 rhachis, forming simple slender racemes which are aggregated toward the summit 

 of the culm ; glumes 1-3-nerved, the first sometimes obsolete ; sterile lemma 

 6-nerved ; fertile lemma leathery-indurated, papillose-striate, with a hyaline mar- 

 gin not inrolled, inclosing a palea of like texture. Annual, mostly weedy 

 grasses, with branching culms, thin leaves, and subdigitate inflorescence. 

 (Name from digitus, a finger.) SYNTHERISMA Walt. 



* Rhachis of racemes with angles wingless ; first glume obsolete ; culms erect. 



1. D. filif6rmis (L.) Koeler. Usually tufted, branching and leafy at the base ; 

 culms slender or almost filiform, 2-7 dm. high; lower sheaths hirsute; blades 

 0.5-2 dm. long, 4 mm. or less wide (rarely wider), hirsute or glabrous on the 

 lower, scabrous on the upper surface ; racemes 1-5, unequal, 3-10 cm. (rarely 

 15 cm.) long, very slender; spikelets 1.7 mm. long, mostly in 3's, appressed, 

 the second and third on slender flexuous pedicels ; glume and sterile lemma 

 densely or sparsely villous between the nerves with white gland-tipped hairs; 

 the glume shorter and narrow, exposing the dark brown acute fertile lemma. 

 (Panicum L.) Sterile or sandy soil, N. H. to Mich., I. T., and southw. - 

 July-Sept. 



2. D. villbsa (Walt.) Ell. Similar to the preceding, usually taller, less slen- 

 der and more densely and constantly hirsute on the sheaths and on both surfaces 

 of the blades; racemes 2-8, more distant (sometimes 3 cm. apart), 6-20 cm. 

 long, much interrupted toward the base; spikelet-clusters usually rather dis- 

 tant; spikelets 2.25 mm. long; the glume and sterile lemma densely matted- 

 villous between the nerves with gland-tipped hairs. Sandy soil, Va. to Mo., and 

 southw. July-Oct. 



* * Rhachis of racemes with lateral angles winged; culms spreading. 

 - Pedicels terete ; first glume obsolete. 



3. D. HUMirtsA Pers. Glabrous ; culms 1.5-4 dm. high, much branched 

 below, ascending or nearly prostrate ; leaves 2-10 cm. long (rarely longer), 3-6 

 mm. wide ; racemes 2-6, aggregated, divergent, often curved, 3-10 cm. long ; 



