58 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



less streaked with white. Much of the root is woody and extremely hard. 

 This deep-seated, widely spreading root habit is very similar to that de- 

 scribed for the same species when growing in the subclimax prairie (Weaver, 

 1919:17). 



Croton texensis. — This widely distributed annual is frequently very abun- 

 dant in sandy soil. A number of plants were excavated near the foot of a 

 sandhill, where they formed an extensive socies. They were about 1.7 feet 

 tall, but had not yet blossomed. They have tap-roots 3 or 4 mm. in diameter, 

 which taper slowly and descend nearly vertically downward, often to depths 

 of 7 or 8 feet. In the first 1.5 feet of soil, and especially in the surface 0.7 foot, 

 the tap-root is usually supplied with 6 to 14 large laterals 0.5 to 2 mm. in 

 diameter, as well as with smaller ones. These usually run off mostly parallel 

 with the surface to distances of 0.5 to 1.5 feet, branching freely and ending in 

 great clusters of poorly branched laterals. Below the 1.5-foot level the tap 

 is seldom more than a millimeter in diameter, but it maintains this thickness 

 almost to its maximum depth. Large branches are few, but there is an abun- 

 dance of threadlike ones from 0.5 to 3 inches long. These are furnished with 

 secondary branches about 0.5 inch in length. This branching occurs through- 

 out, even to the tip. The abundant superficial laterals and their wide spread in 

 the surface soil is a characteristic sandhills root habit, but the great depth of 

 penetration of the tap-root is quite marked for an annual. 



The sandhills near Yuma, Colorado, are a continuation of those in 

 southwestern Nebraska; they are relatively low and, while blowouts 

 are frequent where overgrazing has occurred, large stretches of nearly 

 level sand are to be found. As one leaves the hard lands clothed with 

 their characteristic cover of buffalo and grama grasses and approaches 

 the sandy areas, the first indications of changing soil conditions are 

 given by a greater abundance and better development of Artemisia 

 frigida, Psoralea tenuifiora, Chrysopsis villosa, and Aristida purpurea, 

 and by the appearance of an occasional plant of Ipomcea leptophylla, 

 Stipa comata, Thelesperma gracile, Artemisia canadensis, etc. As 

 the sand increases the short-grass cover gradually gives way to a mixed 

 type of vegetation with Aristida purpurea often dominating, while the 

 still later appearance of Andropogon scoparius and Artemisia filifolia 

 indicates a veiy sandy, permeable soil (plate 9). In typical ungrazed 

 areas the dominants are Stipa comata, Aristida purpurea, Calamovilfa 

 longifolia, Bouteloua hirsuta, and B. gracilis. Kozleria cristata, Andropogon 

 hallii, and Carex pennsylvanica are fairly abundant and important. 

 Andropogon scoparius, which is dominant in an adjoining lowland 

 (plate 7, b), A. furcatus, A. nutans, and Bouteloua curtipendula are 

 characteristic true-prairie elements. Petalostemon purpureus, Liatris 

 punctata, Artemisia gnaphalodes, and Meriolix serrulata intermixed 

 freely with such characteristic plains species as Opuntia camanchica, 

 0. polyacantha, 0. fragilis, Chrysopsis villosa, Plantago purshii, and 

 others. Both Yucca glauca and Artemisia filifolia were very abundant 

 on adjoining grazed areas, but other shrubs w r ere conspicuously absent. 

 The soil was of a firmer type than that at Seneca and quite comparable 

 with that at Haigler. The following species were excavated : 



