ECADS. 113 



two in length, great numbers of tough, fibrous roots a millimeter or less in 

 diameter arise. On 4 cm. of one of these rhizomes 53 roots originated. While 

 some of these pursue a rather vertically downward com'se to a maximum 

 depth of 27 inches, or wander out somewhat obliquely, great numbers, perhaps 

 half, run off more or less horizontally with the surface of the soil, reaching 

 distances varying from 10 to 25 inches on either side of the clump (plate 29, b). 

 Some of these ended only 2 to 4 inches below the soil sm-face, the tips of the 

 growing roots being characterized for a distance of 1 to 3 inches by the entire 

 absence of lateral branches. In fact, some of these had penetrated so near the 

 surface that the soil had dried out and the root-tips had died. However, on 

 mature roots, not only are the tips but also the entire root system densely 

 clothed with great masses of capillary, much-branched rootlets of varying 

 lengths, exclusive of the first 2 to 4 cm., which lie in the dry sand. Most of 

 these branches are only 1 to 3 cm. in length, but frequently the main fibrous 

 roots, especially the deeper-lying ones, repeatedly give off laterals many 

 inches long, which run off at various angles from the course of the main root. 

 While the first 8 inches of soil are literally filled with great masses of this 

 wonderfully efficient absorbing system, the lower soil stratum to 2 feet is also 

 abundantly supplied with fine roots. 



The marked difference in the root penetration of the sandhill ecad as con- 

 trasted with those of the plains may be explained upon the basis of a fairly 

 abundant water-supply in the shallower soils (first 2 feet) of the sandhills as 

 contrasted with the uniformly drier soils of the plains. As pointed out on 

 page 79, the surface sand forms a splendid mulch which inhibits water-loss by 

 evaporation. It may be noted that the plants from the gravelly soils of the 

 knoll in the prairie near Lincoln are intermediate in root depth between the 

 sandhills and the plains ecads. 



Stipa comata. — As described on page 53 and illustrated in plate 19, a, this 

 species is deep-seated in the hard, dry plains soil. The surface 28 inches of 

 soil is thoroughly occupied by the main roots, which are only a few millimeters 

 apart, the interstices being completely filled with horizontal branches. Even 

 to a depth of 32 inches the soil is fairly well filled with much kinked and 

 rebranched threadlike rootlets, while not a few reach a maximum depth of 

 over 5 feet. In addition, the lateral spread of the shallower oblique roots is 

 18 inches or more on either side of the base of the clump. The sandhill ecad 

 of this species, while having a similar surface-root distribution, stands out in 

 marked contrast as regards its superficial position in the soil, a condition 

 already explained upon the basis of a relatively high water-content of the 

 shallow soil. 



Tufts of Stipa comata about an inch in diameter were abundant on the slopes 

 and tops of captured sandhills. Of the 5 clumps examined, rather large roots 

 (to the number of 15 to 25) originated from the base of the crown. None of 

 these exceeded a millimeter in diameter. While some of them descended rather 

 vertically to somewhat obliquely, a few reaching a maximum depth of 23 

 inches, the remainder ran off much more obliquely, having a lateral spread of 

 10 to 15 inches and reaching depths varying from 3 to 20 inches. Although 

 the roots are not branched in the first 1 or 2 inches of soil, they are densely 

 covered with hairs. Upon entering the moist soil they immediately begin to 

 branch, giving off countless numbers of very fine, mostly rebranched short 

 laterals only a few millimeters to an inch in length. At a distance of from 8 

 to 12 inches from the tip, the main roots frequently break up into 3 to 5 

 laterals several inches in length. These spread out in all directions and their 

 profusely branched and rebranched network of finer absorbing rootlets lays 

 hold upon considerable areas of soil. 



