ECONOMIC IMPORTANCE OF GRASSES 



125 



wheat plants. Stoloniferous grasses are those which produce horizontal 

 stems at or above the surface of the soil. The horizontal stems are called 

 runners, or stolons, as in buffalo grass (Buchloe). 



Leaves. The leaves of grasses arise at the nodes, a single leaf at each 

 node. They are arranged in two ranks (distichous) with the third leaf 

 over the first leaf, so that this arrangement is represented by the frac- 

 tion %, standing for the distichy. The grass leaf consists of three parts, 

 the sheath, the ligule and the blade. The sheath is always open, or 

 split, along one side and may be half 

 as long as an internode, as long, one 

 and a half times as long, twice as long 

 as the internode along side of which it 

 arises from the node below. The ligule, 

 or rain-guard, takes on various forms. 

 Usually it is membranous and fits 

 tightly like a collar around the stem 

 preventing the dust-laden rain from 

 running down inside of the sheath (Fig. 

 48). The blade of grass leaves is linear 

 or ribbon-like with parallel veins and 

 usually an acute, or acuminate apex. 

 Grass leaves capable of rolling and 

 unrolling show in cross sections a group 

 of enlarged epidermal cells, between the 

 vascular bundles, the bulliform cells. 

 These cells absorb water in wet weather 

 and the leaves flatten out. In dry 

 weather, the bulliform cells lose water 

 and the leaf blades roll up. 



Inflorescence and Flowers. The grass inflorescence, or flower clus- 

 ter, is a spike of spikelets, a raceme of spikelets, or a panicle of spikelets. 

 The spikelet is the ultimate division of the inflorescence and its parts are 

 arranged in a distichous manner on a shortened axis known as the rachilla. 

 The lower scales of the spikelet are bructlets known as the glumes. These 

 are always empty and do not have flowers in their axils. Above these 

 glumes are the flowers, or florets (Fig. 49). The variations in the mor- 

 phology, arrangement, etc., of the spikelets are of the most diverse kind, 

 and upon these characters depend largely the classification of the grasses. 



FIG. 48. Barley. A, portion of 

 leaf at juncture of leaf and blade; B, 

 stem cut in median lengthwise section. 

 X2^. (Robbins.) 



