1918] 



The Grasses of Illinois 



265 



a new shoot conies up the next spring from a bud formed within the 

 old sheath. These grasses have fibrous roots and form bunches or 

 tufts, and for that reason are often called bunch grasses. Timothy, 

 PMeum prateyise, and orchard grass, Dactylis glomerata, are common 

 examples of this type. In the other type (Fig. 4), the stem dies back 

 to the base, but there are long, creeping rootstocks, or rhizomes, really 

 underground stems, just below the surface of the soil, and the new 

 sho6ts come from these. Such grasses usually form a compact sod, and 

 hence many species are valuable for lawn grasses, as Kentucky blue 

 grass, Poa pratensis. Other common grasses with creeping rootstocks 

 arc redtop, Agrostis alba, and couch grass, Agropyron repens. Be- 

 sides these we have a single species of bamboo, the cane Arundinaria 

 macrosperma, with woody, perennial culms. 



The Grass Plant 



The grass plant consists of root, stem, and leaves. The last two 

 of these are modified to form the inflorescence. 



Boot. — The grass plant has slender, fibrous roots which are usually 

 very numerous at the base of the plant (Fig. 3). In the corn plant 

 and occasionally in other grasses, roots are developed from the lower 

 nodes and act as prop, or brace roots (Fig. 5a). 



Stem. — The stem of the grass plant is called a culm. In all but 

 very young plants the culm is usually hollow except at the more or 

 less swollen nodes (Fig. 6a). In maize and sorghum the stems are 

 filled with pith. The parts of the culm between the nodes are called 

 internodes (Fig. 6b). The culms are nearly always cylindrical, as in 

 the corn stalk (Fig. 7), but they may be flattened, as in Canada blue 

 grass, Poa comprcssa (Fig. 8). They are never three-angled, as in 

 the sedges. 



Leaf. — The leaves are borne at the nodes and consist of two parts, 

 the sheath and the blade. The sheath (Figs. 7a and 9a) is wrapped 



Figs. .'5-11. — 5, Lower portion of grass culm Avith brace roots; G, Culm split 

 to show (a) the solid node, (b) the intcrnode; 7, Cylindrical culm; 8, Flattened 

 culm; 9, Portion of leaf showing (a) sheath, (b) blade, (c) ligule; 10, Ligule 

 a ring of hairs; 11, Ligule membranous, fringed with hairs 



