THE PRAIRIES. 



9 



reached a maximum depth of 46 inches, although below 2 feet the roots are 

 very sparse (plate 6, b). The largest roots are only 0.5 mm. in diameter. The 

 laterals are usually not over an inch long. These abundant threadUke laterals 

 branch only poorly. The roots are brownish white in color and of a very firm 

 textiue. Other groups of plants examined in two locations on alluvial soils 

 showed a somewhat poorer development of the root system, but the general 

 distribution and depth were very similar to those growing in the gravelly soil. 

 This root distribution stands quite in 

 contrast to that found by Shantz in Col- 

 orado. This would seem to be a clear 

 case of environmental conditions pro- 

 foundly modif>dng root development. 



Liatrls punctata. — Of the numerous 

 blazing-stars which add beauty to the 

 prairies in autumn, L. punctata and L. 

 scariosa are probably the most abundant. 

 The xeroph>i}ic nature of the former and 

 its extensive range far into the drier 

 regions westward may be explained in 

 part by its deep root system. 



Seven individuals of this species were 

 excavated. All had strong tap-roots. 

 Those growing in clay with a sandy sub- 

 soil reached depths of 11 feet 5 inches 

 and 15 feet 9 inches respectively, while 

 three growing in clay-loam with a clay 

 subso3 penetrated only to a depth of 

 about 6 feet 8 inches. A diagram of one 

 of the larger specimens (fig. 2), recon- 

 structed from a photograph and from a 

 drawing made to scale in the field, 

 pictiu'es the roots as occurring in one 

 plane. On other specimens small laterals were very scarce to a depth of 9 

 feet, while at 12 feet the soil was filled with small, silvery white, sparsely 

 branched rootlets. This scarcity of absorbing laterals was again noted in the 

 clay-loam soil of the high prairie until a depth of about 6 feet was reached. 

 Even here the branching was not so pronounced as on the specimens in the 

 lighter soil. The older roots are woody and chocolate-brown in color. 



Liatrls scariosa. — This plant, unhke L. punctata with its strong deep tap- 

 root, is characterized by a large woody corm, 3 to 5 inches in diameter, from 

 which arise very numerous fibrous roots. These are only 1 to 2 mm. in diam- 

 eter, but they are very finely branched and spread laterally, thus thoroughly 

 occup>dng the first 2 feet of soil. The depth of penetration was not deter- 

 mined. 



Solidago rigida. — This goldenrod is not only abundant in the less xero- 

 phytic prairies of Minnesota and Nebraska, but extends far westward into the 

 drier grasslands. In Wyoming and Montana its presence, together with 

 certain other species, invariably indicates rather permeable soils with at least 

 a fair amount of available water.^ 



^ During the summer of 1917 the writer, while working on grazing problems in the prairies of 

 the Northwest, had an excellent opportunity to trace the westward extension of many species 

 typical of the less xerophytic prairies of eastern Nebraska and Minnesota far into the Great 

 Plains. Indeed, of the two associations of the prairie-plains climax of Clements (1916), 

 the Stipa-Agropyrum prairie occupies much more territory in the Northwest than the Bulhilis- 

 Bouteloua plains. 



Fig. 1. — A meter quadrat in the 5owte- 

 loua community dominating a 

 gravelly ridge at Belmont, 

 near Lincoln. 



B, Bouteloua gracilis. 

 A, Andropogon furcatus. 

 S, Sporoholus longifoUus. 

 M, Meriolix serrulata. 

 Am, AmoT'pha canescens. 



