408 



WEED FLORA OF IOWA 



D 



*4! 



o 



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

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



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

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

 grounds. 



GRAMINEAE, GRASS FAMILY. 



Johnson Grass (Sorghum halepense (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 (Sorghum halepense). 

 (Drawn by Charlotte M. King.) 



inflexed margins; the third glume 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. 



