HOW TO KNOW THE GRASSES 



20a. Fertile floret brownish-black when ripe; leaf sheaths glabrous. 



Fig. 300. 



SMOOTH CRABGRASS Digitaria ischaemum (Schreb.) Muhl. 



Annual; erect or spreading, often root- 

 ing at the lower nodes; culms usually 15 

 — 40 cm. long; inflorescence usually of 

 2 — 6 racemes. This species frequently 

 grows with the next and is a bad weed 

 in lawns. Disturbed soil, fields, waste 

 places, gardens, lawns. Augvist — Oc- 

 tober. Introduced from the Old World. 



Figure 300 



20b. Fertile floret pale or leaden gray when ripe; leaf sheaths sparse- 

 ly to densely covered with long straight hairs. Fig. 301. 



CRABGRASS Digitaria sanguinalis (L.) Scop. 



Annual; erect or spreading, usually rooting at 

 the lower nodes; culms up to 1 m. long, the 

 plants often forming large mounds on rich soil. 

 Crab grass is a serious weed in lawns. Being 

 originally from warm climates, it starts growth 

 when hot weather arrives. The rampant plants 

 soon make large patches in lawns, but die out 

 after the first frosts. They also grow abundant- 

 ly in fields and waste places, sometimes furnish- 

 ing some forage. July — October. Introduced 

 from the Old World. 



Figure 301 



21a. Spikelets placed with the back (convex side) 

 of the fertile lemma toward the rachis of the 

 raceme. Fig. 302 22 



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Figure 302 



158 



