ROOT SYSTEMS OF MIXED-PRAIRIE SPECIES. 57 



about a centimeter or less in length, arising at infrequent intervals along its 

 course. The tap-root was fairly well branched throughout. At a depth of 

 0.3 foot, three threadlike branches occurred; at 0.5 foot two laterals, each 0.5 

 mm. in diameter, arose; while three branches, 1 mm. in diameter, came off at 

 1.6 to 1.7 feet, and still another 0.2 foot deeper; besides these, numerous fine 

 branches ran off for distances of only 0.2 to 0.4 foot. The larger laterals 

 spread widely. Some ran rather horizontally away from the tap for distances 

 of 2.5 to 3.3 feet before turning downward. Even in the surface 0.2 to 0.5 foot 

 of soil, laterals were traced to a distance of 2.5 feet from the base of the plant. 

 Many of these larger laterals reached depths of 2.5 to 3 feet, while one ended at 

 a maximum depth of 3.8 feet. The laterals are only poorly rebranched. 

 However, the root-ends, including the last foot, are fairly well supplied with 

 rootlets, most of which are unbranched. Thus it may be seen that this 

 species has the characteristic widely spreading root habit, and that although 

 rather meagerly supplied with small laterals, the root system is adapted for 

 absorption in relatively shallow soil layers. 



Ceanothus ovatus. — This low shrub is quite common, not only in the sub- 

 climax and true prairies, but in the mixed prairie of the sandhills as well. The 

 pubescent variety is more common than the glabrous form in the latter area. 

 Here the individual plants become much branched and very bushy, reaching 

 heights of 1.5 to 3 feet and forming clumps 3 to 25 feet in diameter. They 

 frequently dominate even the highest hills and sometimes occur in such 

 abundance as to shade out most other species. 



Two large specimens, both about 10 years old, were excavated. They had 

 strong woody tap-roots an inch in diameter. On one the crown was buried 

 a foot in the sand. From its three major parts 12 stems arose to a height of 1.3 

 or 1.5 feet, the whole forming a bush over 3 feet in width. The top of the other 

 plant was somewhat smaller. In the first 2 feet of soil, but especially in the 

 surface 1.5 feet, large numbers of fine roots, a millimeter or less in diameter, 

 arose not only from the tap-root but also from the buried stems. These ran 

 off somewhat parallel with the surface soil for distances varying from 0.2 foot 

 to over 3 feet. These roots afford a considerable absorbing area in the surface 

 soil for this shrub and permit it to compete directly with sandhill grasses for 

 the water afforded by light showers. Between a depth of 2 and 3 feet, 7 large 

 laterals from 3 to 6 mm. in diameter were given off by one plant. They 

 spread widely (3 to 5 feet from the descending tap-root) and pursued very 

 tortuous courses, but ultimately turned downward, reaching depths of 9 to 11 

 feet. The other plant gave off 4 similar laterals at a depth of about 3.3 feet. 

 At a depth of 5 feet the tap-roots were 10 and 14 mm. in diameter respectively. 

 A foot deeper, the one broke up into two nearly equal branches, both of which 

 pursued crooked downward courses. At 9 feet, one of these branches had 

 wandered a distance of 3.6 feet horizontally from the base of the crown; the 

 other now turned abruptly quite across the 4-foot trench before again running 

 downward. Roots of both plants were traced to a depth of 12 feet, further 

 excavation not being made because of the caving sand. Even at this depth the 

 tap-roots were a millimeter in diameter. Besides the branches described, 

 numerous others (both short and long) were given off at intervals at all depths, 

 the whole root branching and rebranching freely. While some of the roots 

 blanched coarsely and ended abruptly, others formed a most delicate mass of 

 absorbing rootlets. Even below 10 feet some of the deeper roots threw off 

 laterals abundantly in the moist sand, although others ran for a foot or more 

 without branching. Most of the roots were bright red in color, except the 

 older parts, which were reddish brown. All but the oldest parts are more or 



