ECADS. 77 



made at many stations throughout this region, we must accept the judgment 

 of the plant as an indicator of available moisture at least periodically in the 

 deeper soil layers. 



Bouteloua gracilis. — This grama grass is a dominant not only in the short- 

 grass plains, where it forms extensive consociations, but it plays an important 

 part as a species in the layer of mixed prairie. It also occurs in alternes on 

 the lighter soils of uplands in true prairie, where it may also often be found on 

 areas of alluvial soil on bottom lands. From the standpoint of grazing, it 

 ranks very high among the grasses, being equaled only by Bulbilis dactijloides. 



The roots of this species have been described for a consocies growing as an 

 alterne in a glacial deposit of very porous, coarse, sandy to gravelly loam soil 

 on a ridge in the true prairie near Lincoln, Nebraska. The root system was 

 found to be well-developed, great masses of fine roots occupying every cubic 

 centimeter of soil to a depth of 1.5 feet. A few roots reached a maximum 

 depth of 3.8 feet, although below 2 feet they were very sparse. Other groups 

 of plants examined in two locations on alluvial soil showed a somewhat poorer 

 development of the root system, but with a general distribution and depth 

 very similar to those growing in the gravelly soil. 



This grass has also been examined in the mixed prairie at Colorado Springs. 

 The soil was well filled with fine rootlets to a depth of 2.5 feet, while in the 

 next 0.5 foot they were still fairly abundant, some of the longer ones penetrat- 

 ing to a maximum depth of 4 feet. Further examinations of this species 

 were also made in "adobe" soil in pure short-grass land about 25 miles south- 

 east of Colorado Springs, where it was the dominant (plate 11, a). Roots 

 were found to be very abundant to a depth of 3.3 feet, while several were 

 traced to a maximum depth of 4.3 feet. 



During 1919 still further examinations of this species were made at Sterling, 

 Colorado, and Ardmore, South Dakota. At the former station (plate 2, a) 

 the soil was quite filled with roots to a depth of 2.5 feet, while at 3.2 feet they 

 were still abundant. The maximum depth of penetration was 4.2 feet. 



At Ardmore, where grama was competing with wheat-grass and buffalo 

 grass (p. 75), the roots were abundant to the working depth of 3.6 feet, while 

 some were traced to a depth of 4.3 feet in the tenacious but moist Pierre clay. 



A comparison of these data shows that grama-grass roots, like those of 

 buffalo grass, are quite deep-seated. The working depth ranges from 1.7 to 

 over 3 feet, while the maximum root depth in every case was between 3.8 feet 

 and 5.8 feet. Little difference in root distribution was found in the several 

 plant communities, except that the marked development of widely spreading 

 surface laterals so common in the more arid portions of the grassland formation 

 was not found in the true prairie. Here the specimens examined, like those of 

 Bulbilis, spread but little in the surface soil. 



Agropyrum glaucum. — This important dominant of true and mixed prairies 

 has now been examined at five different stations in Nebraska, Colorado, and 

 South Dakota. A complete description of its root habit, in both high and low 

 true-prairie areas, may be found on page 18 (c/. fig. 3 and plate 12, b). The 

 chief difference in its root habit in the true and mixed prairies, besides greater 

 depth of penetration in the former is in the absorbing system near the soil 

 surface. This is very much better developed in the drier mixed-prairie soils 

 (cf. Weaver, 1919:52). At both Ardmore, South Dakota, and at Limon," 

 Colorado, where it grew in competition with Bulbilis, the latter station being 

 on typical short-grass silt loam, the absorbing system in the surface soil was 

 quite pronounced. In the Pierre clay at Ardmore the working depth was at 

 5.5 feet and the maximum root penetration 7 feet. At Limon this grass was 



