408 



WEED FLORA OF IOWA 





FiQ. 237. Achenes, "seeds," of common forms of Sedges (.Carer). 

 (After Hillman, Bull. Nevada Agr. Bxp. Sta.) 



aehene; seed may appear with or without tubercle and bristles. 

 Seed occasionally found in seed of alsdke and red clover from wet 

 grounds. 



GRAMINEAE, GRASS FAMILY. 



Johnson Grass {Sorghum halepen^e (L.) Pers.). 



Sessile spikelet broadly lanceolate, acute, 4-6 mm.* long, be- 

 coming dark at maturity ; callus small, obtuse, shortly and sparsely 

 barbate ; first glume coriaceous, slightly pubescent on the flattened 

 back, 5-7 nerved; second similar, equal to first, with hyaline, ciliate, 



Fig. 238. Spikelet of Johnson Grass (.SorghMm halepense'). 

 (Drawn by Charlotte M. Kins.) 



inflexed margins; the third glTime shorter, membranous, faintly 

 2-nerved, with ciliate, infolded margins; fourth glume broad, ob- 

 tuse, shorter than second, 2-lobed at apex, ciliate, awned; awn 

 10-16 mm. long ; palea shorter than glumes, without nerves, ciliate. 



Smooth Crab Grass {Digitaria humifusa Pers.). 



Spikelets lanceolate or elliptical, one-twelfth in. in length, acut- 

 ish; glumes usually present, first glume wanting, sometimes rudi- 

 mentary, 3-nerved; the first and second, hairy on the margins; 



•1 mm. = 0.0394 Inch, or nearly one-twenty-fifth Inch. 



