:^98 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 34 



To the farmer or stockman grass may mean almost any herbaceous 

 plants upon which animals graze, including clovers, alfalfa, and 

 other legumes. Indeed, the English word grass is derived from 

 the same root as graze, grass being the principal part of grazed 

 herbage. 



STRUCTURE 



The structures which the various grasses have in common and 

 which together distinguish them from other families are the jointed 

 stems, hollow as in wheat, or pithy with solid joints or nodes as in 

 corn and sorghum; leaves alternate in two ranks, and consisting of 

 two parts, the sheath and the blade, the sheath surrounding the stem 

 like a tube, the blades diverging more or less. Any plant with such 

 a stem and such leaves is a grass. 



INFLORESCENCE 



The inflorescence or flowering part of grasses is borne at the top 

 of the stem or at the ends of the branches. The flowers are borne 

 in the axils of bracts on minute specialized branchlets called spike- 

 lets. The flowers are inconspicuous, without calyx or corolla. They 

 consist of a single pistil with a one-celled ovary, two styles with 

 feathery stigmas, and usually three stamens. Each flower is borne 

 between two small green bracts. The ripened ovary, the grain, has 

 a small embryo and a large mass of starchy endosperm. The " germ " 

 of a kernel of corn is the embryo ; the rest of the kernel is endosperm. 

 At the base of the spikelet are two empty bracts, the glumes. These 

 are very large in the oat, and minute in bluegrass. The spikelet 

 may contain a single floret (the flower with its two bracts) as in 

 recltop and timothy; two or three as in the oat, or several to many, 

 as in bluegrasses, fescues, and brome grasses. The florets, like 

 the leaves on the culm, are always two-ranked. 



If we examine a head of wheat we find a central flat zigzag axis 

 with spikelets about half an inch long in an overlapping row on 

 each side. In bearded wheats the spikelets bear long awns or bris- 

 tles. Each spikelet contains several bracts (in rows), within which 

 are the flowers as described above. 



The form of the inflorescence in grasses is very diverse, and it is 

 this which gives the characteristic aspect to the different species. 

 Barley and rye have heads or spikes like wheat. In oats the large 

 spikelets are borne on long pedicels in an open panicle. In recltop, 

 bluegrass, and the fescues the spikelets are borne in rather loose 

 panicles, whereas in timothy the panicle branches and pedicels are 

 so short that the spikelets are closely packed in a cylindrical head 

 or spike. In sugarcane, giant reed (Arundo), and pampasgrass 

 {Cortaderia) there is a large number of spikelets in a great feathery 



