84 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



no roots of wire-grass extended below a depth of 2.8 feet. They were poorly 

 developed throughout. At Sterling the lateral spread was about as described 

 at Colorado Springs; no roots penetrated below a depth of 2.3 feet. It should 

 be recalled that growth conditions on the rolling land here are even less favor- 

 able than on the level country at Burlington, as is indicated by the open mat 



type of vegetation (plate 2). 



Aristida was further examined at Yuma, but this time in the sand. Several 

 well-developed but somewhat isolated plants were found growing on a sandy 

 ridge The finer sand had been blown away and the plants were rooted in 

 coarse sand which was firmly compacted. Three plants were excavated. 

 On one medium-sized bunch, 3.5 inches in diameter, 189 roots were counted. 

 Figure 29 shows a 'bisect about 4 inches wide through one of these clumps. 



FlG> 29.— Bisect through the roots of Aristida purpurea growing in the sandhills. 



This clearly illustrates the shallow root habit, the widely spreading roots, and 

 the very abundant and relatively long lateral branches, the whole forming a 

 very different root system from those growing in loam or clay. While there 

 were practically no roots under the clumps, the lateral spread in the surface 

 5 foot of soil reached 2 to 3 feet, some of the deeper roots spreading even 

 more widely. No roots were found below 2.5 feet, and practically the entire 

 system was confined to the surface 2 feet of soil. Rebranched lateral rootlets 

 were very abundant, some of the main laterals reaching a length oi 4 or 5 

 inches, but they were mostly shorter. The root-ends were well-branched. 

 A final examination of this species was made in a broad valley about a mile dis- 

 tant where the compacted sand was somewhat intermixed, at least near the 

 surface, with some black soil and humus. The area was dominated by Andro- 

 pogon scoparius, with some Aristida purpurea growing in a short-grass turl 

 of Bouteloua gracilis, B. hirsuta, and species of Carex (plate 7, b). the roots 

 had a very wide lateral spread in the shallow soil. Some ran off nearly parallel 

 with the soil surface at depths of only 2 to 6 inches for distances of about 2 feet 

 At 1.3 feet depth some exceeded 2 feet in lateral spread. The surface 1.5 feet 

 of soil especially was filled with the coarse but well-branched roots of this 

 species. Moreover, many of the roots (perhaps about a fourth of the whole 

 root system) penetrated rather vertically downward, so that the soil below 

 the plants was also well occupied. . 



From the above it is clear that the root habit of this species vanes con- 

 siderably with the environment. The wide lateral spread, especially m the 

 surface 6 inches of soil, and the general root development was much more 

 pronounced in every case where the species was excavated m a sandy -sub- 

 stratum Under these conditions the normal lateral spread of 0.4 to U.7 loot 

 in silt-loam or clay soil was extended to 2 or 3 feet; in fact, many of the roots 



