THE SANDHILLS SUBCLIMAX. 



73 



groups, ranging from 2 to 5 mm. in diameter. The larger branches, after 

 diverging somewhat from the main tap, took a downward course similar to that 

 of the main root. At 6 feet the tap divided up into a group of 3 or 4 roots 

 of almost the same size, which after diverging took the usual downward course 

 and at a depth of 10 feet were 2 to 3 nmi. in diameter. At this depth repeated 

 caving of the sand made further digging so dangerous that the work was 

 abandoned. 



Artemisia filifolia. — In the sandhill mixed association, aside from the two 

 grass dominants, Calamovilfa and Andropogon hallii, the sand-sage is the most 

 conspicuous plant. This is due both to its shrubby habit and its great abun- 

 dance. It is indicative of a light type of soil with considerable moisture pene- 

 tration. It drops out in the more compact hard lands of the plains. 



Three plants were examined. They were growing on a stabiHzed area near 

 the sand-dune. The largest had a tap-root 1.5 inches in diameter, from which 

 arose a large number of stems to a height of 2 feet, forming a bush about 18 

 inches in diameter. The strong, vertically descending, woody tap-root 

 tapered gradually and uniformly to a depth of 32 inches, at which point it 

 broke up into 3 laterals, the largest 0.5 inch in diameter and the other two but 

 slightly smaller. Some of these were traced to a depth of 9 feet, where they 

 were still 4 nam. in diameter (fig. 25). In the surface 30 inches of soil the tap 

 gave off 6 large laterals, from 6 to 13 mm. in diameter, and a very large 

 nimiber of smaller ones, some of them but 0.5 mm. thick. These branches 

 formed a rather distinct surface absorbing system, and showed a strong 

 tendency to run out in a direction parallel with the surface. In fact, some 

 of them terminated in soil which was shallower than the depth at which they 

 originated. These with their branches and the numerous rootlets from the 

 somewhat oblique larger roots formed a dense network confined to the first 

 30 inches of soil. This was characteristic of all the plants examined and was 

 not unlike the root habit of Eriogonum. Some of these larger branches ran 

 off laterally to distances of 2 to 5 feet before turning downward. Although 

 they branched somewhat freely at intervals in the fourth to seventh foot of 

 soil, they often pursued their tortuous courses for long distances, sending off 

 hardly any laterals. 



The relative abundance of the shallower roots as contrasted with the deeper 

 ones, together with their lateral spread and the extent of their branching, is 

 well shown in figure 25. Unfortunately, because of the loose texture of the 

 soil, it was unsafe to trace them to greater depths. The roots are dark brown 

 in color, the older portions having a rough, fissured bark. The younger ones, 

 and especially those in the deeper soil, were exceedingly brittle. The plant 

 here described was 10 years old. The lower branches and divisions of the tap 

 were very sparsely branched, the few rootlets being of the same character as 

 those nearer the surface. From the description and figure it will be seen that 

 while this species has a strong tap-root, it also has a highly developed absorb- 

 ing and binding system characteristic of the general group of sandhill plants. 



Tradescantia virginiana. — This spiderwort is rather common in the sand- 

 hills. The plants were examined on a partially captured blowout. They had 

 a rather fleshy root system. As many as 18 of these fleshy roots, varying from 

 1 to 2 nam. in diameter, were foimd arising from the base of a single stem (fig. 

 26); some passed down almost vertically to a maximum depth of 19 inches; 

 others started down more or less vertically, then with a gradual curve out- 

 ward ended from 6 to 8 inches from the vertical; others passed more or less 

 obHquely downward from the stem. The greater part of these fleshy roots, 

 however, formed a surface absorbing system which spread out in all directions 



