188 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Fruits indurated-rigid (or if thin not open at the summit nor 

 hyaline-margined). 



Spikelets placed with the back of the fruit turned away 

 from the main axis. 



First glume and rachilla joint forming a swollen ring- 

 like callus; fruit mucronate or shortly awn-pointed. 



22. Eriochloa (p. 207). 

 First glume present or wanting, not forming a ring-like 

 callus; spikelets in slender racemes. 



First glume as long as the spikelet or nearly so; 

 spikelets swollen on the side toward the axis and 

 fitting into alternate hollows; inflorescence a sin- 

 gle raceme 27. Mesosetum (p. 211). 



First glume wanting or not over one-fourth the 

 length of the spikelet. 



Racemes racemose along the main axis; first 



glume present 28. Brachiaria (p. 212). 



Racemes digitate or subdigitate, first glume 



wanting 20. Axonopus (p. 207). 



Spikelets with the back of the fruit turned toward the main 

 axis. 



Spikelets plano-convex, subsessile in spike-like 

 racemes, typically lacking the first glume (both 

 glumes wanting in P. pulchellum). 



19. Paspalum (p. 199). 

 Spikelets unequally biconvex; paniculate, or if race- 

 mose the first glume present. 



Fertile florets 2 23. Isachne (p. 208). 



Fertile floret 1. 



Glumes awnless. 



Second glume broad and saccate, panicle 

 i niitracted or spike-like. 



30. Sacciolepis (p. 212). 

 Second glume not broad nor saccate. 



Margins of lemma inrolled; no lateral 

 appendages nor excavations at base 



of fruit 32. Panicum (p. 214). 



Margins of lemma not inrolled; either 

 lateral appendages or excavations 

 at base of fruit. 



33. Ichnanthus (p. 228). 



(ilumes or one of them awned, or cuspidate. 



Fruit cuspidate, palea free at the tip; 



second glume and sterile lemma tapering 



into an awn or cuspidate point. 



31. Echinochloa (p. 213). 

 Fruit not cuspidate, palea not free; awns 

 arising from a toothed summit. 



Spikelets clothed with rose-colored 

 silky hairs; first glume minute. 



34. Tricholama (p. 229). 



Spikelets pubescent with short pale 



hairs, first glume nearly as long as 



the second. 35. Oplismenus (p. 229). 



