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



FLORAL ORGANS 



The floral organs of all flowering plants are modified shoots. The 

 flowers of grasses consist of stamens and pistils with no floral envelops 

 or perianth, except as they are represented by the lodicules. 



THE INFLORESCENCE 



The unit of the grass inflorescence is the spikelet. The spikelets 

 are nearly always aggregated in groups or clusters winch constitute 

 the inflorescence. The tassel of maize, the spike or head of wheat or 

 timothy, and the panicle of the oat or bluegrass are examples of 

 inflorescences. 



The simplest inflorescence is the raceme, in which the spikelets are 

 pediceled along an axis. The typical raceme, as in Pleuropogon, is 

 rare in grasses. Modified spikelike racemes are characteristic of 

 Paspalum, Digitaria, and allied genera, in which the spikelets are 

 paired and short-pedicellate, and of most Andropogoneae, in which 

 the spikelets are paired, one sessile the other pedicellate. The 

 inflorescences of the groups mentioned may best be considered as 

 specialized panicles. 



The spike differs from the raceme in having sessile spikelets. In 

 the Hordeae the spikes are symmetrical, in the Chlorideae they are 

 one-sided. 



The panicle is the commonest kind of grass cluster. In this the 

 spikelets are pediceled in a branched inflorescence. The panicle may 

 be open or diffuse as in Panicum capillare or contracted as in millet. 

 Compact panicles, especially if cylindric like timothy, are called 

 spikelike panicles. 



Numerous small inflorescences may be aggregated into a large or 

 compound inflorescence. Many Andropogoneae have compound 

 inflorescences, for example, the broomsedge (Andropogon virginicus). 



Panicles often expand at the time of flowering (anthesjs). Such 

 expansion or spreading of the branches and branchlets is brought 

 about by the swelling of motor organs (pulvini) in the axils of the 

 inflorescence. 



Sometimes the ultimate branches of an inflorescence are sterile 

 instead of bearing spikelets. The sterile branchlets of Setaria, 

 Pennisetum, and Cenchrus are modified into bristles around the 

 spikelets. 



THE SPIKELET 



A typical spikelet consists of a short axis (rachilla) on which the 

 flowers are borne in the axils of two-ranked imbricate bracts. The 

 spikelet is, therefore, a reduced modified shoot in which the rachilla is 

 a stem bearing at each node a reduced leaf (bract). The flowers are 

 secondary reduced shoots borne in the axils of the bracts, the first 

 bract (palea) on the secondary shoot being a modified prophyllum 

 and the stamens and pistil being modified leaves or bracts. The 

 bracts of the lowest pair on the rachilla, being always empty, are 

 distinguished as glumes. The succeeding bracts are called lemmas 

 (flowering glumes of some authors). The glumes and lemmas repre- 

 sent the sheath of the leaves, the blades not developing (in proliferous 

 spikelets the parts are partially developed into typical leaves). The 

 lemma, palea, and included flower are called the floret. The 

 branchlet bearing the spikelet is the pedicel. 



