ECADS. 



117 



or clusters, both on the main root and larger branches. Besides these, all 

 of the roots examined had 3 to 6 or more larger branches, which ran off from 

 the tap somewhat horizontally at all levels and to distances varying from a 

 foot to over 3 feet. As shown in figure 55, the root system as a whole 

 is poorly branched, although the sandhill ecads were much better provided 

 with laterals and smaller rootlets than were the specimens examined in the 

 plains soil. The root is yellowish-brown to nearly black in color. It is very 

 brittle, the laterals especially being followed with extreme difficulty. 



A comparison of these descriptions, together with an examination of the 

 two figures, reveals the fact that the sandhill form, while showing the same 

 habit of a strong tap-root which penetrates to about the same depth as the 

 plains species, differs in its more abundant branching as well as in the great 

 lateral spread of the branches. In these respects the modifications are not 

 unhke those of other sandhill ecads already described. 



Kceleria cristata. — This very important and cosmopolitan grass was first 

 examined in the prairies of eastern Washington, where it is a common bunch- 

 grass. Under the prevailing conditions of rather moderate precipitation 

 (about 21 inches), most of which falls in winter and is followed by a season of 

 simmier drought, it flowers in late June, soon dries up, and remains dormant 

 imtil revived by the autumn rains. In this region the deepest root found w£is 

 at 28 inches and 15 inches was determined as the average maximum depth. 

 In the prairies of eastern Nebraska it is also an important grass, growing under 

 an annual precipitation of 28 inches, much of which falls during the growing 

 season. Here none of the roots of the 7 plants examined reached depths of 

 over 21 inches, while the average maximum root depth was about 15 inches. 



Kceleria was further examined in the hard plains soils of east-central 

 Colorado and under an annual (summer) precipitation of about 15 inches. 

 Here the root distribution was almost identical in lateral spread and depth 

 with those already described. The greatest depth was 26 inches and the 

 average maximum depth about 14 inches. Finally, the same species was 

 excavated on a half-gravel-slide at an elevation of 9,000 feet in the Rocky 

 Mountains. As was characteristic in the other habitats, the first 6 to 8 inches 

 of soil was completely filled with the profusely branched and matted root 

 system. Roots were quite abundant to a depth of 12 inches, while some of 

 the longest penetrated to 18 or 20 inches. 



A comparison of plates 5, a, and 26, a, showing the roots of plants from the 

 prairies of eastern Nebraska and from the gravel-shde respectively, reveals 

 the fact that they are almost identical. Compared with the profound differ- 

 ences in the ecads of Stipa comata and Elymus triticoides, Kceleria is a remark- 

 ably stable species. 



Chrysopsis villosa. — This composite is widely distributed throughout much 

 of the grassland formation, occurring abundantly in the sandhills (plate 21, a). 

 On the plains several plants were examined. All had strong tap-roots, which 

 were woody for 2 or 3 feet. The height of the plant above ground was 6 to 10 

 inches. A second plant had a tap-root with a diameter of 12 mm. It pene- 

 trated almost vertically downward, except for local curves and kinks, usually 

 less than an inch from a vertical line, to a depth of 8.6 feet (fig. 56). The first 

 18 inches of the tap, beginning about an inch below the soil surface, is abun- 

 dantly supplied with threadlike laterals, mostly less than a milhmeter in 

 diameter, which run out in a horizontal direction from a distance of 1 inch to 

 more than a foot. These laterals are practically free from branches. At a 

 depth of 6 to 18 inches, half a dozen stronger laterals, each about 1 mm. in 



