268 Bulletin No. 205 [March, 



The .Spikelet 



The spikelet may consist of a single flower or of a number of flow- 

 ers. As the classification of grasses is based primarily on the characters 

 of the spikelet, it is essential to know something of its structure. 



The stalk of the spikelet is known as the pedicel. The spikelet con- 

 sists of a short axis, called the rachilla, which bears one or more flow- 

 ers. The rachilla may be jointed to the pedicel either above or below 

 the glumes. 



TJie Glumes. — At the base of the spikelet are two empty bracts, 

 which are called glumes. They are designated as the first, or outer 

 glume (Fig. 15a), and the second, or inner glume (Fig. 15b). They 

 are usually easily distinguished from the other parts of the spikelet 

 by the difference in shape, texture, number of nerves, amount of hairs 

 present, etc. Sometimes the first glume is very small, as in Syn- 

 tlierisma sanguinalis (Fig. 32), or it may be wanting, as in the species 

 of Paspalum (Fig. 41). Both glumes are absent in Homalocenchrus 

 (Fig. 108). Sometimes the glumes are awncd, as in Elymus canaden- 

 sis (Fig. 280). 



Tlie Lemmas. — The lemmas are the bracts of the spikelet found 

 within and above the glumes (Fig. 15c) . Their number varies with the 

 number of flowers found in the spikelet. There is usually a flower at 

 the base of each lemma ; if the flower is sterile, the lemma is called 

 a sterile lemma. The lemma often differs from the glumes in texture, 

 being sometimes much thinner, and sometimes, as in Panicum, much 

 hardened. It is often awned (Fig. 147) ; the awns are sometimes spi- 

 rally twisted or bent (Figs. 124 to 133). 



The Palea. — The palca (Fig. 15d) together with the lemma serves 

 to inclose the stamens and pistil. It is usually two-nerved and like its 

 lemma in texture. 



The Stamens. — There are usually three stamens (Fig. 16b), but 

 the number varies from one to six. 



The PistU.— In our species there is a single pistil (Fig. 16a), 

 which has a one-celled ovary, two styles (rarely one), and two feathery 

 stigmas. 



The Fruit. — The grass seed, so-called, is in reality a fi-uit (a 

 caryopsis), the seed being inclosed in the ripened ovary. 



