MANUAL OF THE GRASSES OF THE UNITED STATES 9 



The spikelet may be reduced to a single floret (Agrostideae), some- 

 times with a prolongation of the rachilla behind, as in Calamagrostis. 

 In Andropogon a fertile spikelet is paired with a sterile one in which 

 the pistils or both pistils and stamens are absent. The upper florets 

 of the spikelet are often reduced in Festuceae and the lower lemmas 

 may be empty in some genera (Uniola, Distichlis). In Melica and 

 Chloris the upper florets may be reduced and form a club-shaped 

 body. In Phalaris there is one fertile floret with a pair of sterile 

 florets below, each reduced to a small appressed scale. In Lamarckia 

 and Cynosurus there are prominent sterile spikelets mixed with the 

 fertile ones. 



In Paniceae the spikelet has a perfect terminal floret and below 

 this a sterile floret, consisting of a sterile lemma similar to the glumes, 

 either empty or with a hyaline palea or sometimes with a staminate 

 flower. 



In a few grasses (Amphicarpum, Chloris chloridea) there are, in 

 addition to the usual inflorescence aboveground, cleistogamous spike- 

 lets borne on underground culms. 



RACHILLA 



The axis bearing the florets, the rachilla, usually disarticulates 

 between the florets when the spikelet is more than one-flowered. In 

 many species of Eragrostis it is continuous, usually bearing the per- 

 sistent paleas, after the remainder of the florets have fallen. When 

 the rachilla disarticulates the break is usually just below the florets 

 so that the rachilla joint remains attached as a little stipe back of the 

 palea. The disarticulation is near the middle of the internode in 

 Trichoneura and Festuca subuliflora. The rachilla disarticulates just 

 above the floret in Phragmites, the rachilla remaining as a plumose 

 stipe below it. The rachilla is short-villous or pilose in many genera 

 of Aveneae (the callus of the floret often pilose also). 



In some genera with one-flowered spikelets (Calamagrostis, Cinna, 

 Cynodon) the rachilla is prolonged behind the floret as a slender, often 

 villous, joint or bristle, and in several genera with several-flowered 

 spikelets (Koeleria, Poa) it is prolonged beyond the uppermost floret. 



GLUMES 



The glumes are usually similar in shape and texture, the first often 

 smaller and with fewer nerves. Rarely the first glume is longer than 

 the second (species of Aristida). The first may be much reduced or 

 wanting (Axonopus, Paspalwn, Digitaria). Rarely both glumes are 

 wanting (Leersia, Reimarochloa) . In Eriochloa the first glume is re- 

 duced or wanting, the first rachilla joint being a hard ring below the 

 spikelet. In Andropogoneae the first glume is usually indurate, 

 sometimes strongly so. In some Horde ae the glumes are bristlelike. 



The lemmas in the more primitive grasses are typically similar to 

 the glumes but may be variously modified. In Panicum the fertile 

 lemma is much harder than the glumes; in Andropogoneae the}- are 

 much thinner than the glumes, often hyaline. The indurate cylindric 

 lemma of Stipa and Aristida bears a sharp callus at base, formed by 

 the oblique articulation with the rachilla. 



