ROOT SYSTEMS OF MIXED-PRAIRIE SPECIES. 65 



spots, although the surface soil may be quite sandy, is indicated by 

 such stable mesophytes as Poa pratensis ; hence the excavation of sand- 

 hills plants was carried on elsewhere. The following species were 

 studied : 



Panicum scribnerianum— This species usually plays the role of an inter- 

 stitial among the taller prairie grasses, occurring in both moist and dry soil. 

 In the sandhills, however, it sometimes becomes dominant over local areas. 

 It was examined at the base of a hill where it was growing very abundantly. 

 The individuals are connected by short rhizomes. The fibrous roots are very 

 abundant. They are only about 0.3 mm. in diameter, except near the growing 

 tips, which are often a millimeter thick. They are very tough and quite easily 

 excavated. They have a lateral spread of approximately 2 feet from the base 

 of the plant. This maximum lateral spread is reached at a depth of about 

 1 to 1.7 feet. Few roots were found running parallel with the soil surface. 

 Beyond this depth the roots usually penetrate more or less vertically down- 

 ward. While some are only a foot long, many, including most of those that 

 pursue a vertically downward course from their origin, reach depths of 3 feet; 

 still others grow as deep as 3.9 feet. All of the roots are very abundantly 

 supplied with multitudes of well-branched laterals 0.5 to over 2 inches in 

 length (plate 14, a). 



Tradescantia occidentalis. — The western spiderwort forms societies, espe- 

 cially in sandy soil, in both the true and mixed prairies of the grassland forma- 

 tion. The large blue or reddish flowers make the plants quite conspicuous 

 from early spring to midsummer. A half dozen individuals of this species, 

 all full-grown and in blossom, were excavated on the crest of a sandy hill. 

 They have fleshy roots, 2 or 3 mm. in diameter, of which 15 or 20 occur on a 

 single plant. Some of these take a- course almost parallel with the soil surface 

 and extend off for distances of 1 to 1.5 feet, where the roots end at depths of 

 only 0.3 or 0.4 feet. Others run obliquely, but seldom vertically downward, 

 Some reach depths of 3 feet, but most of the roots lie in the first 1.5 feet of soil. 

 Few roots were found just beneath the base of the plant; they are fleshy, tan- 

 colored, and very brittle, especially the younger parts. Nor is the diameter 

 uniform, some portions enlarging to almost twice the size of other parts. The 

 roots throughout are very poorly branched. Indeed, they branch scarcely at 

 all, except at infrequent intervals along their course, and these laterals are 

 usually less than an inch in length and entirely unbranched. In general, this 

 shallow, widely spreading root system is similar to that of Tradescantia 

 virginiana (Weaver, 1919:74), except that it is more extensive but much less 

 branched. 



Bouteloua hirsuta. — Hairy grama, like Bouteloua gracilis, is a species of 

 wide distribution and diverse ecological habit, forming a sod in its northern 

 range and growing in isolated clumps in the southern part. This habit also 

 varies with the water-content conditions. Both species furnish excellent 

 forage for all classes of stock and, like buffalo grass, are exceedingly valuable 

 for winter forage, since they "cure" on the ground. Bouteloua hirsuta is more 

 drought resistant than B. gracilis and so fills an important place in the drier 

 regions, especially on sandy plains; in fact, it reaches its best development on 

 stable sandy or sandy-loam soils. 



This grass was excavated on the lower slope of a sandy hill, where, as in the 

 adjacent valley, it was dominant, forming a rather dense sod. The soil was 

 very sandy to a depth of at least 6 feet, except the surface foot, which con- 



