56 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



rhizome. They are usually less than 2 mm. thick. Many of them spread 

 widely in the surface soil. Even in the first inch or two of soil, roots were 

 traced laterally for distances of 0.8 to 2.3 feet. These were well supplied with 

 laterals only an inch in length and about 0.5 inch apart all along their course. 

 These roots often end in the surface soil with a fairly good brush of mostly 

 unbranched rootlets. Frequently the larger roots also give off, in addition to 

 these shorter rootlets, branches 6 to 10 inches in length and fairly well re- 

 branched. They run in all directions, but only a few directly downward. 

 The threadlike bushy rootlets form a good absorbing system in the surface 

 soil. Some of the larger roots, after running out laterally and often more 

 obliquely than those described, turn downward and reach a maximum depth 

 of 4.8 feet. Thus, while many roots end in the surface soil, perhaps half of 

 them run obliquely outward from 1 to 2 feet or more; then turning, they pen- 

 etrate to depths of 5 or 6 feet. They are branched very poorly, except in the 

 last 1 to 1.5 feet. Although the branching in the first 6 inches from the rhi- 

 zome is very poor, small roots in this region are densely clothed with root- 

 hairs. Such a root system is especially efficient in absorbing water and 

 solutes in the surface soil as well as at much greater depths. 



Cyperus schweinitzii. — This perennial sedge thrives in sandy soil. While 

 perhaps more often a component of stabilized vegetative areas, it is frequently 

 found among the pioneers or forming families in the shifting sands of blowouts. 

 It is characterized by short tufts made up of a few grasslike, spreading stems 

 and produces a very open type of the bunch-grass form. 



Several clumps, about 2 feet high and in fruit, were examined in an old 

 blowout. These plants originated from short, hard, woody, much-branched 

 rhizomes 2 to 4 mm. in diameter, which were found at depths of 3 to 6 inches. 

 Hard, sharp-pointed buds arise from the thickened corm-like bases of the 

 erect stems. From the base of the stems and from the rhizomes arise great 

 numbers of fibrous roots, scarcely more than 0.5 mm. in diameter. These 

 almost immediately begin to give rise to great clusters of exceedingly fine and 

 minutely branched laterals which permeate the soil in all directions. The 

 laterals are very well branched to the second and third order with hair-like 

 branches from 2 mm. to 2 or 3 inches or even more in length. They are espe- 

 cially well developed in mat-like areas in the surface soil. In fact, most of the 

 root system occurs in the surface foot of soil, while practically all of the root 

 system lies above the 1.7-foot level, although a few branches penetrated to 2.3 

 feet. The lateral spread is very great. Roots were traced parallel with the 

 soil surface at depths of only 0.2 to 0.3 foot for distances of over 3.5 feet. 

 This shallow-rooting habit is shown in plate 13, a. The dark-brown, rather 

 tough roots were readily excavated. It is quite probable that this shallow, 

 widely spreading root system in more stabilized areas becomes, because of 

 competition, much deeper seated. 



Thelesperma gracile. — This perennial species is a subdominant over a wide 

 range of territory in the more arid portions of the grassland formation. It 

 frequently forms extensive societies both on the hard land and in sandy soil. 

 A number of plants were examined in an area only poorly clothed with vege- 

 tation. A single typical specimen will be described. It had a tap-root 4 mm. 

 in diameter, which gave rise to 4 flowering stalks about 1.8 feet high. The 

 dark tan-colored tap-root ran vertically downward, tapering very slowly 

 and reaching a maximum depth of 3 feet. At a depth of 0.3 foot a branch 1.5 

 mm. in diameter came off and ran almost horizontally into the hillside, where, 

 at a distance of 1.7 feet and a depth of 1.3 feet, it gave rise to a new plant. 

 This underground part was unbranched and had only a few threadlike rootlets, 



