ROOT SYSTEMS OF MIXED-PRAIRIE SPECIES. 49 



The large fleshy tap varies from 12 to 25 mm. in diameter, often being thicker 

 in the deeper soil than at its point of origin. These light-tan-colored roots are 

 very brittle; they are definitely characterized by a very tortuous course, turn- 

 ing at sharp angles, and frequently by much twisting and looping (fig. 18). 

 The branches, both large and small, often arise where the roots turn, abruptly. 

 Some of the major laterals are as large as the tap-root; and indeed the tap-root 

 may split up, usually at considerable depths, into branches of almost equal 

 size. Several of the main roots were traced beyond a depth of 8 feet, the 

 caving sand not permitting further excavation. It is probable that they 

 penetrated 2 or 3 feet deeper. This is perhaps the most poorly branched root 

 system examined in the sandhills. Even the limited number of small branches 

 that do occur end abruptly and have only a few small unbranched laterals. 



Haplopappus spinulosus. — This composite has a wide distribution through- 

 out the drier portions of the grassland formation from Canada to northern 

 Mexico. It is a subdominant, frequently occurring in extensive societies. 

 This species was examined on a fairly well covered slope in mixed prairie. 

 It had a strong woody tap-root, 8 mm. in diameter and dark brown in color, 

 which ran almost vertically downard and tapered rather rapidly, so that at a 

 depth of a foot it was only 2.5 mm. thick; below this point it narrowed slowly 

 to its end at a depth of 5 feet. Most of the branches were thrown off in the 

 first foot of soil. The largest were not over 2 mm. in diameter, while many 

 were threadlike (fig. 19). The larger laterals ran obliquely outward and down- 

 ward, so that at a depth of a foot they had reached their maximum distance of 

 1 to 1.3 feet horizontally from the base of the plant. Below this depth they 

 ran rather vertically downward to distances of 3.5 to 4.5 feet. Like the tap- 

 root, these laterals are clothed with a great number of rather poorly branched 

 whitish rootlets. These stand out in striking color contrast to the larger 

 brown roots. These finer rootlets are 1 to 5 inches (usually 2 or 3 inches) in 

 length and end with very little branching. Below 1 foot the tap was poorly 

 branched to a depth of 2.5 feet, where some long laterals originated, as shown 

 in the drawing. In the moist sand the root-endings were fairly well branched, 

 but with rather coarse laterals. This species is illustrative of a moderately 

 branched, rather wide-spreading, and fairly deep-seated root system. 



Meriolix serrulata. — This primrose is an estival bloomer of wide distribu- 

 tion. It occurs not only in mixed prairie, but frequently also in the short- 

 grass plains. It reaches its best development and forms the most marked 

 societies, however, in the true prairie. In drier areas it is usually much 

 dwarfed and the bright-yellow flowers are much smaller. Several plants were 

 examined. They were growing on a partly covered, sandy hillside. They 

 have woody tap-roots, 8 to 15 mm. in diameter and of a reddish-brown color. 

 The propagation of the plant by its widely spreading underground parts is 

 shown in figure 20. In places the sand had blown away and left portions of 

 these unearthed. All of the larger roots are characterized by their lax and 

 meandering courses. While reaching a depth or distance from the base of the 

 plant of only 2 or 3 feet, they may actually be 4 or 5 feet long. Both the tap- 

 root and its major branches taper very slowly. While well supplied with 

 larger branches, which often originate in a dichotomous manner, smaller 

 branches are not very abundant. Usually the root termini are well branched 

 and occasionally fairly well-branched sublaterals occur. The maximum 

 depth of root penetration was found to be 4.5 feet. The characteristic meand- 

 ering course, wide spread, and depth of penetration is well illustrated in 

 figure 20. 



