s 



MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



leaves). The lemma, palea, and in- 

 cluded flower are called the floret. 

 The branchlet bearing the spikelet is 

 the pedicel. 



The spikelet may be reduced to a 

 single floret (Agrostideae), sometimes 

 with a prolongation of the rachilla be- 

 hind, as in Calamagrostis. In Andro- 

 pogon a fertile spikelet is paired with 

 a sterile one in which the pistil or 

 both pistil and stamens are wanting. 

 The upper florets of the spikelet are 

 often reduced in Festuceae, and the 

 lower lemmas may be empty in some 

 genera ( Uniola, Blepharidachne) . 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 ap- 

 pressed scale. In Lamarckia and 

 Cynosurus there are prominent sterile 

 spikelets mixed with the fertile ones. 



In Paniceae the spikelet has a per- 

 fect 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. 



t In a few grasses (Amphicarpum, 

 Chloris chloridea) there are, in addi- 

 tion to the usual inflorescence above 

 ground, cleistogamous spikelets borne 

 on underground culms. 



RACHILLA 



The axis bearing the florets, the 

 rachilla, usually disarticulates be- 

 tween the florets when the spikelet is 

 more than 1-flowered. In many species 

 of Eragrostis it is continuous, usually 

 bearing the persistent paleas, after 

 the remainder of the florets have 

 fallen. When the rachilla disarticu- 

 lates 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 1-flowered 

 spikelets (Calamagrostis, Cinna, Cyno- 

 don) the rachilla is prolonged behind 

 the floret as a slender, often villous, 

 stipe or bristle, and in several genera 

 with several-flowered spikelets (Koe- 

 leria, 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 sec- 

 ond (species of Aristida). The first 

 may be much reduced or wanting 

 (Axonopus, Paspalum, Digitaria). 

 Rarely both glumes are wanting 

 (Leersia, Reimarochloa) . In Eriochloa 

 the first glume is reduced or wanting, 

 the first rachilla joint being a hard 

 ring below the spikelet. In Andro- 

 pogoneae the first glume is usually in- 

 durate, sometimes strongly so. In 

 some Hordeae the glumes are bristle- 

 like. 



LEMMAS 



The lemmas in the more primitive 

 grasses are typically similar to the 

 glumes but may be variously modi- 

 fied. In Panicum the fertile lemma is 

 much harder than the glumes; in An- 

 dropogoneae they 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. 



PALEA 



The palea is mostly 2-keeled and 

 often concave between the keels. It is 

 homologous with the prophyllum. 

 Sometimes the 2 nerves of the palea 

 are so close together as to appear like 

 a single nerve (Cinna) ; sometimes the 

 2 nerves are marginal and widely sep- 

 arated as in rice. The keels may be 

 ciliate (Eragrostis), bearded (Tri- 

 plasis), or winged (Pleuropogon) . The 

 palea is much reduced or wanting in 



