16 



THE ECOLOGICAL RELATIONS OF ROOTS. 



brown to almost black in color, the younger parts are lighter in color and 

 herbaceous. Short laterals (about 9 cm. in length and mostly devoid of 

 branches) occur 5 to 25 mm. apart. This branching may continue to the tip, 

 which is about 0.3 mm. in diameter and is poorly branched. On the larger 

 specimen two laterals occurred (plate 11, a). The larger of these ran off at a 

 depth of 5 feet and at an angle of about 60° to a distance of 28 inches. It was 

 almost destitute of branches. The roots are tough and easily followed. The 

 coal-black streaks within the cortex and stele make their identification easy. 

 Although extending somewhat deeper, these specimens correspond rather 

 closely with those examined in the clay-loam soil at Lincoln. 



Lygodesmia juncea. — This perennial stem-xerophyte is common in prairies 

 throughout Nebraska and is often abundant on the crests of ridges or other 

 dry situations. A trench about 8 feet long and 3.5 feet wide was dug on a 

 slope just below a group of these plants and more than a dozen roots were 

 examined. The tap-root, varying from 2 to 6 mm. in diameter, may give rise 

 to several plants by means of short branches 2 to 8 inches below the surface 

 (plate 11, b). 



The roots descend in an almost vertically downward course and frequently 

 in parallel groups only a few inches or indeed a few milhmeters apart, to 

 distances of 15 to 20 feet or more. At these depths the tips are frequently 

 only 1 or 2 feet from a vertical line with the top. The roots are fleshy, very 

 brittle, especially after a depth of 3 or 4 feet is reached; they are from hght 

 cream to dark brown in color and exude a white latex upon injury. The side 

 of the trench was dotted with drops of latex, showing the abundance of the 

 cut roots. This character aids greatly lq recovering the broken ends of these 

 brittle roots. Branching occurs not at all, except for tiny laterals less than 

 1 mm. in diameter and an inch in length, which come off very sparingly at 

 almost right angles and at intervals of 6 to 12 inches. These tiny laterals are 

 poorly or not at all branched, the secondary branches being only 1 to 2 mm. 

 long. The tap narrows slowly and is frequently 2 mm. in diameter at a depth 

 of 16 to 18 feet. Numerous roots occurred at 18 feet in depth and one was 

 traced to a maximum distance of 20 feet 7 inches. Here it was still 2 mm. in 

 diameter. Because of the danger of caving of the mellow loess soil, deeper 

 excavation was abandoned. The loess was of very uniform texture through- 

 out and well moistened to the depth examined. 



Lespedeza capitata. — This tall, conspicuous legume is comanon throughout 

 central and eastern Nebraska. It is very abundant on the lower slopes of the 

 loess hill, where 6 or more plants were examined. The very characteristic 

 light-yellow roots are much branched just below the surface, where numerous 

 strong laterals, 5 to 7 mm. in diameter, run off in all directions, some almost 

 horizontally at depths of only 3 to 6 inches. These large laterals branch very 

 irregularly but profusely, giving rise to numerous finely branched roots which 

 fill the surface soils to a distance of 2 or 3 feet on either side of the plant, when 

 the main branches may turn abruptly almost vertically downward (plate 

 11, c). In addition to these shallower roots, which compete with many of the 

 grasses for the water in the surface layers of soil, numerous other branches 

 pursue a more or less vertically downward course from the outset and reach 

 depths of 5 or 6 feet or more. These, with the vertical extremities of the 

 horizontal laterals, which may also reach similar depths, furnish a very exten- 

 sive absorbing area for the plant. The deeper roots taper rapidly, but all are 

 furnished with short rebranched laterals. Even the root-ends are well- 

 branched, but no matting was observed, as in the case of several of the other 

 legumes. A maximum depth of 7 feet 10 Laches was recorded. 



