ECADS. 75 



of these "sinks" in such a manner that while one end was in the buffalo-grass 

 area, the other permitted the excavation of the bordering wheat-grass, 

 Psoralen, and mountain sage. The wheat-grass roots thus growing in com- 

 petition with the buffalo grass are described elsewhere (p. 78), but it may be 

 noted here that the roots of the two species grew at the same depth. Both 

 grasses were abundant to a level of 4.3 feet, where the very hard, black soil 

 was underlaid with sand and both had a maximum depth of 5.2 feet. The 

 wheat-grass was only 1 to 1.2 feet high (plate 11, b). 



Further examination of this species was made late in June in the mixed 

 prairie at Phillipsburg, Kansas, over 230 miles eastward. The better con- 

 ditions for prairie express themselves not only in the greater development of 

 species, but also by the presence of many true-prairie forms. Andropogon 

 furcatus was second only to A. scoparius in importance; Agropyrum glaucum 

 reached a height of 3 feet, and often controlled over extensive areas, while 

 Elymus canadensis was abundant. Societies of Psoralea tenuiflora, Erigeron 

 ramosus, Coreopsis tincioria, and Ratibida columnaris were very conspicuous at 

 this time. In many places the layer of Bulbilis dactyloides and other short- 

 grasses and sedges was present, while in pastured areas the buffalo grass 

 formed a dense sod in which isolated clumps of Psoralea reached a height of 

 about 2 feet. 



The soil is a dark-brown silt-loam, with some sand intermixed to a depth of 

 about 1.7 feet, where it becomes more clayey, although when moist it takes 

 on a dark-brown color to a depth of 4.5 feet. Below this it becomes lighter in 

 color and more clayey in texture. In all of the four trenches, some of which 

 were made on tilled land (p. 119), it was moist enough to hold firmly when 

 molded by the hand at all depths to over 7 feet. The buffalo-grass roots were 

 examined in the same trench with the tall-grass competitor, Andropogon 

 scoparius. Both had a maximum root depth of about 6 feet. The short- 

 grass roots were very abundant to a depth of 2.5 feet and fairly abundant at 

 the 5-foot level, while not a few reached the maximum depth of 6 feet and some 

 penetrated even deeper. 



A final examination of this species was made in the mixed prairies near 

 Ardmore, South Dakota. A trench was dug to a depth of over 8 feet in an area 

 where the tall wheat-grass (2 to 2.3 feet high) was competing with the buffalo 

 and grama grasses (plate 3, b). All showed an excellent growth, Bouteloua 

 gracilis being 10 to 12 inches high. At a depth of 6.7 feet the very hard Pierre 

 clay gave way to a layer of sand. The soil was fairly moist throughout. As 

 at Yuma, the working depth of Bidbilis was about 4 feet, while the maximum 

 depth of penetration exceeded 7 feet. For the sake of comparison the preced- 

 ing data are brought together in table 7. 



Study of these data reveals a number of interesting facts. The roots of 

 buffalo grass, as regards working depth and maximum depth of penetration, are 

 little affected apparently by environmental conditions. They are just as deep- 

 seated in the short-grass plains as in the mixed or true prairie. One marked 

 difference in root habit, however, should be emphasized. Plants examined in 

 the less xerophytic grassland at Lincoln scarcely spread at all laterally. In the 

 mixed prairies at Phillipsburg and at Ardmore the lateral spread in the 

 surface soil was well developed, but not to such a marked extent as among the 

 individuals growing at the various stations in the short-grass plains. The 

 roots reach a working depth beyond the "hard pan," even where this is well- 

 developed. "Hardpan" is thought to arise as a result of the water penetrating 

 repeatedly only to a depth at which this harder layer is formed, thus not only 

 washing down the finest soil particles but also causing them to be more or less 

 firmly cemented together by the accumulated solutes carried downward. It 



