68 THE ECOLOGICAL EELATIONS OF ROOTS. 



V. THE SANDHILLS SUBCLIMAX. 



In order to compare root development more extensively under 

 different environmental conditions, work was continued in a sandhill 

 area of Colorado adjoining the plains community and located about 

 40 miles southeast of Colorado Springs. Since general climatic con- 

 ditions are almost identical with those described for the plains, any 

 differences in root development may be attributed to edaphic causes. 

 An excellent description of the sandhill communities, considered in the 

 light of their successional relation, has been given by Pool (1914). 

 Shantz (1911) also gives a thorough treatment of Colorado sandhill 

 vegetation from the standpoint of its indicator significance in regard 

 to crop production. The general character of the sandhills and their 

 characteristic vegetation is shown in plates 20, b, and 21, a. 



Redfieldia flexuosa.— This grass is at home in the sandhills. Indeed, it is 

 the most abundant and controlling species of blowout pioneers. While it 

 may be mixed with other pioneers, it is often the only plant present in such 

 situations. The usually sparse and rather small clumps are connected by 

 means of very long, coarse, tough rhizomes, which sometimes reach a diameter 

 of 4 to 5 mm. but are usually smaller; they are frequently many feet in length 

 and may be traced for a distance of 20 to 40 feet on the surface where the sand 

 has been blown away from them. Because of the shiftmg sand, the depth at 

 which they occur is variable. Living rhizomes with vertically descending 

 branches were found at a depth of 38 inches and they are rather abundant 

 between this depth and the surface, some running horizontally, others 

 obliquely and sometimes almost vertically. 



From the nodes of these tough rhizomes, which are from less than an inch to 

 6 inches apart, whorls of roots arise in addition to sharp-pointed buds. These 

 consist of 2 to 10 roots, but are usually 3 to 5. The roots vary greatly in 

 length, diameter, and direction of growth, depending upon the age and posi- 

 tion of the rhizome. Those near the tip of the sharp-pointed, much elongated 

 rhizome may be less than 1 inch in length, very fleshy, 2 to 4 mm. in diameter, 

 and practically destitute of branches. Others a foot or two from the tip are 

 12 to 20 inches long and are covered with a fine absorbing system of short 

 rootlets, except for the 4 to 6 inches of the growing end. The older roots, 

 which are well branched to the very tips with much divided laterals 1 to 3 

 inches long, reach a maximum depth of 56 inches. They are often 2 to 4 mm. 

 in diameter. They not only run rather vertically downward, but also diverge 

 at all angles, even to the horizontal. Long, well-branched roots were traced 

 to distances of over 3 feet from the base of the plant at depths of 4 to 8 inches. 

 The laterals from these frequently ascend vertically upward and end in well- 

 branched termini only 2 to 3 inches below the surface. Thus the length, 

 position, and abundance of this rather coarse root system, together with the 

 rhizomes, equip Redfieldia flexuosa in an effective manner for life in the 

 shifting but moist soil of the sand-dune (fig. 23). 



Calamovllfa longifolia.— The sand-reed is also an efficient sand-binder. 

 It is frequently found associated with Redfieldia fiexuosa, Psoralea lanceolata, 

 and other pioneers in the shifting sands of the blowout, but normally occurs 

 with Andropogon hallii and others somewhat later in the succession. 



It forms a veritable mat of roots and rhizomes to a depth of 34 inches. A 

 wide trench 6 feet long and over 5 feet deep was dug on a small dune which was 



