THE SANDHILLS SUBCLIMAX. 



71 



inch of sand, the ghstening white roots are rather destitute of branches, but 

 below this level all of the roots are densely covered with multitudes of very 

 fine absorbing laterals. Indeed, a single inch of an average root was found to 

 have approximately 75 of these hairlike absorbing laterals. While many of 

 them are only a few millimeters long, others reach a length of 6 to 10 inches. 

 All are profusely and minutely branched, the larger ones to the third and fourth 

 order. Thus this wonderfully efficient root system is able to penetrate all 

 portions of the sandy substratum and to extract the available water, while 

 at the same time it forms a very effective means of preventing sand from 

 blowing. 



Sporobolus cryptandrus. — In aerial habit this grass is not unhke Gala- 

 movilfa. It ranks as a dominant among sandhill grasses. Three clumps of it 

 were examined in two separate trenches on a half-captured blowout. As a 

 whole, it is characterized by an extremely fine fibrous root system, the main 

 divisions of which arise from a short stocky rhizome 2 to 4 inches in length. 

 On a single rhizome 1.5 inches long, 40 of these main roots were counted. As 

 they leave the rhizome they pass off in all directions, some vertically, some 

 obliquely, and a great many of them almost parallel with the surface, but 

 gradually growing deeper as they pursue their course, so that at a maxi- 

 mum distance of 18 to 20 inches many were found at 6 to 8 inches below the 

 surface. The maximum vertical depth of penetration found was 22 inches. 

 From the point where the major divisions of the roots leave the rhizomes, 

 they are covered with a dense growth of root-hairs which hold the sand firmly 

 and give the roots the appearance of being much greater in diameter than they 

 really are. They are actually threadlike, usually less than 0.5 mm. in diameter 

 and very tough. These roots are slightlj^, if at all, branched for a distance of 

 2 or 3 inches from the rhizome, but from that point on to the very extremity 

 they are well supplied with branches from an inch or less to 8 or 10 inches long. 

 These branches pass out in all directions from the main root and are them- 

 selves exceedingly finely branched and rebranched to the third and fourth 

 order, so that the soil for a depth of from 10 to 13 inches is well filled with this 

 fine, delicate absorbing system. 



Eriogonum microthecum. — As shown in plate 21, a, this Eriogonum fre- 

 quently controls local areas on sandy slopes and occurs rather widely through- 

 out the sandy plains area. The plant has a multicipital stem, which at a 

 depth of 4 to 8 inches merges into a strong tap-root 0.5 to 1 inch in diameter. 

 At a depth of 2 or 3 inches the tap-root begins to branch, and for a depth of 

 2.5 to 3 feet sends off an extraordinary absorbing system (fig. 24). Some of 

 these branches arise singly, but it is common to find 2 to 4 springing from 

 approximately the same point. In diameter they vary from 1 to 5 mm. The 

 general tendency of the branches is to pursue an almost horizontal course from 

 a distance of a few inches to 2 feet and then turn almost vertically downward, 

 penetrating the sand to a depth of 18 inches to 3 feet. A few of these branches, 

 however, instead of taking this course, pursued an almost horizontal course to 

 their very tips, which were sometimes 3 feet from the tap. These laterals for 

 the first few inches of their course as they left the tap-root were very sparsely 

 branched, the distance depending upon the size of the root. Beyond that 

 point the branches gradually became more numerous and as one approached 

 the extremities the number was so great as almost to form a conspicuous 

 network in the fight sand. As the main laterals and their larger branches 

 approached their lower extremities, the little rootlets were so numerous as to 

 form fairly brushy tips. Below 3 feet the branches of the tap were much 

 fewer in number and much larger in size. As a rule they seem to occur in 



