. The ecological relations of roots . Fig. 9.—Aristida purpurea. Fig. 10.—Artemisia frigida. MuWenbergia gracilliina.—This grass is also a dominant of the short-grassplains; it is less widely spread and less abundant than Bouteloua gracilis,though in some places it ranks close to the latter. Superficially, it appears likeBulbilis dadyloides, because of its mat-like growth in small areas and the short,curled leaves. Frequently the center of the mat is dead and only theperipheral portions produce flowers. A trench over 4 feet long was dug with, one face cutting through a purestand of this grass
. The ecological relations of roots . Fig. 9.—Aristida purpurea. Fig. 10.—Artemisia frigida. MuWenbergia gracilliina.—This grass is also a dominant of the short-grassplains; it is less widely spread and less abundant than Bouteloua gracilis,though in some places it ranks close to the latter. Superficially, it appears likeBulbilis dadyloides, because of its mat-like growth in small areas and the short,curled leaves. Frequently the center of the mat is dead and only theperipheral portions produce flowers. A trench over 4 feet long was dug with, one face cutting through a purestand of this grass to a depth of about 5 feet. Great clusters of roots, onlyabout mm. or less in diameter, ran off in all directions from the very sur- 48 THE ECOLOGICAL RELATIONS OF THE PLAINS ASSOCIATION. 49 face to the average working depth, and are abundantly supplied with short,much rebranched laterals. Many of these spread very widely laterally,branching and rebranching into both long and short termini, so that thesurface 27 inches of soil is completely filled with a dense network of absorbingrootlets. Every cubic centimeter of the soil to a depth of 2 feet is occupied bya network of this absorbing system. At a depth of 27 inches most of the root-lets end in very much branched termini, but a few penetrate to greater dis-tances. By undercutting the face of the trench and working upward from adepth of 5 feet, several of these threadlike rootlets were encountered at adepth of 55 inches. The roots are tan in color. Gutierrezia sarothrse.—^This half-shrub occurs throughout the plains region,although it is usually more abundant in areas of less thoroughly disintegratedsoil or in overgrazed areas. In such situations it forms extensive plants examine
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