50 Rhodora [March 



In all, several hundred measurements have been made, and the 

 constancy of size for each species and variety is remarkable. The 

 measurements of anthers given in the key are all from herbarium 

 material, and are probably somewhat smaller than would be those 

 made from fresh material. The presence or absence of stamens in 

 the lower floret seems to characterize a fundamental group of spe- 

 cies, but the presence or absence of the palet of this floret, though 

 generally reliable, breaks in two species, and is probably not of pri- 

 mary importance; also the presence of the ligule is apparently not 

 fundamentally important as a group character, though valuable in 

 separating species. The perennial or annual habit, on the contrary, 

 seems to be more fundamental. 



The following key is really a synopsis in key form of the species, 

 varieties and forms of Echinochloa in North America. It is based 

 on the material in the Gray Herbarium, Herbarium of the New Eng- 

 land Botanical Club, Herbarium of the New York State College of 

 Agriculture, and the Herbarium of Mr. F. Tracy Hubbard; also 

 some types have been seen at the New York Botanical Garden. In 

 the lists of specimens given in the text following the synopsis many 

 specimens have been omitted in regions where the species is common. 



a. First floret with or without a palet, neutral, very rarely 

 staminate; lower glume inserted close to the upper or 

 but slightly distant; ligule wanting or rarely a trace in 

 E. oplismcnoidcs, but ligular region sometimes pubes- 

 cent; plant glabrous except in E. Walteri, annual, in 

 low or upland soils. 

 b. Spikelets 4.5 mm. long or less, ellipsoid, ovoid or oval, 

 from scarcely echinatc to very strongly and coarsely 

 so. 

 c. Upper glume not awned, except rarely in E. muri- 

 cata; lower lemma awned or awnless; spikelets 

 ellipsoid or ovoid; anthers 0.3-1 mm. long. 

 d. Spikelets ovoid or oval, approaching ellipsoid in 

 varieties of E. zelaycnsis; coriaceous lemma 

 ovate or oval. 

 e. Coriaceous lemma subacute or obtuse, the tip 

 withering; spikelets moderately echinate to 

 almost unarmed, never appearing very bristly 

 to the unaided eye. 

 /. Panicle narrow, usually open; branches short, 

 1-2.5, rarely 4 cm. long, slender, usually 

 simple, the small (2-2.9 mm. long), oval, 

 unarmed, often obtuse, scarcely echinate 

 spikelets in few rows; leaf -blades 3-6 mm. 

 broad; (coriaceous lemma obtuse; anthers 

 0.7-0.8 (-0.9) mm. long; lower palet pres- 

 ent; branch- and nodal hairs of the panicle 

 usually poorly developed; low slender 

 grasses) . 



