FORM AND STRUCTURE 7 



occur in different ways : if the branches form single 

 spikelets and the lowest glumes appear sessile upon the 

 main axis, the inflorescence is a spike ; if the spikelets are 

 formed only upon further divided or secondary branches, 

 it is a panicle. 



5. Spikelets. The unit of inflorescence is the spike- 

 let, and, as above stated, its form is dependent upon the 

 arrangement of the latter. It consists of a much short- 

 ened, close-jointed axis, having two-ranked, modified 

 leaves or bracts. The lower two of these are known as 

 glumes proper, which are followed by a flowering glume 

 recently called lemma, which partly incloses a branch 

 bearing sexual organs, protected also on the other side 

 by a bractlet called a palea having its back toward 

 the axis of the spikelet. Occasjonally, as in barley and 

 rice, the spikelet is one-flowered. Often the flowers 

 that are present are not all fertile. Either glumes or 

 sexual organs are sometimes rudimentary. Lemmas are 

 frequently awned, and usually have a middle nerve. They 

 frequently extend downward on the axis from their point 

 of insertion. This portion grown to the axis is separated 

 from the free part by a furrow called the callus. The 

 palea is generally more delicate in texture than the lemma, 

 has its edges usually turned in, and has usually a furrow 

 instead of a midrib. 



There are sometimes opposite the palea and above the 

 lemma two small scales called lodicules, standing with 

 their edges touching and grown together at their bases. 

 These are usually considered to be two parts of a rudi- 

 mentary perianth, a third part of which (the posterior 

 lodicule) is found in certain other grasses, although Hackel 

 regards the two anterior lodicules taken together as a 

 second palea and the posterior as a third. When these 



