THE PLAINS ASSOCIATION. 



51 



about 4 feet downward these branches gave off occasional laterals about 2 to 

 4 mm. in diameter, which extended from a few inches to a foot or more. These 

 laterals tended to take a more or less horizontal direction. 



The color of the root is dark brown. It was very thick and fleshy and 

 extremely brittle, so much so that near the terminus great difficulty was 

 found in following it. Throughout its length, whenever broken, a clear to 

 milky fluid exuded in limited quantities. The surface of the root was extremely 

 rough and pitted; its diameter was often irregular. Throughout the whole 

 course two or more branches had a tendency to twist about each other. This 

 was marked in branches occurring not more than 2 feet from the surface, 

 again at intermediate depths, and still again at not less than 6 inches from the 

 extreme depth. 



Yucca glauca. — ^The soap-weed is a widely distributed species, being 

 especially abundant on dry, sandy, rocky slopes and forming extensive 

 societies throughout many areas in the plains association. Its size, duration, 

 and often its abundance combine to make it an important species. From the 

 standpoint of the stockman it is often a bad weed. 



A number of specimens were examined. An excavation was made about 

 two large plants growing 2 feet apart. They each sent down a strong caudex 

 3 inches in diameter, but neither of them reached a depth greater than 18 

 inches. At this depth they branched and ran off laterally in a direction either 

 parallel with or ascending toward the surface. The two plants were connected 

 by a large underground rootstock (plate 17, a), while another (over 2 inches 

 in diameter) ran off at nearly right angles from the connecting rootstock and 

 reached the surface 3 feet beyond. It had given rise to several small plantlets. 

 From the multicipital stem as many as 25 to more than 50 rosettes of leaves 

 arose. Many of these were dead. One crown measured 21 by 26 inches in 

 diameter, this being only a medium-sized plant. It reached a height of 30 

 inches. The multicipital branching extended to a depth of 5 to 7 inches and 

 profound contractions were in evidence. 



Beginning at the very surface, the stems are supplied profusely with roots. 

 These vary from 2 to 4 mm. in diameter and run off horizontally to great 

 distances, the lateral spread being remarkable. A number of these hori- 

 zontal roots were traced to a distance of 32 feet (fig. 12). They occupied the 

 soil chiefly at a depth of 6 to 18 inches, and, because of a somewhat tortuous 

 course, terminated at a horizontal distance of 27 feet from the caudex from 

 which they arose. These roots are reddish in color, of nearly uniform diameter 

 for long distances, and very sparingly branched. Only at intervals do short, 

 usually unbranched, secondary laterals occur. The cortex is thick and fleshy 

 and serves for water storage; upon the death of the older roots it shreds off 

 and reveals the tough wiry stele. The abundance of these roots is surprising. 

 In a single square foot of vertical trench face, at a depth of 18 inches, 54 roots 

 were counted. They extend outward in all directions from the rhizome, as 

 was proven by digging a series of small trenches at distances of 18 to 20 feet 

 on all sides of isolated specimens. Invariably Yucca roots were found. Such 

 a trench, dug halfway between two isolated Yucca plants 66 feet apart, 

 revealed the presence of laterals. Thus it may be seen that these large plants 

 absorb water and soil solutes over a very extensive area in direct competition 

 with the grasses. 



A trench 6 feet long and 7 feet deep revealed very few Yucca roots below 2 

 feet. However, some do occur and penetrate to maximum depths of about 

 7 feet. Like the shallower laterals, the deeper ones are poorly branched, even 

 the tips having few branches and ending abruptly. The ends are not more 

 than 0.25 to 0.2 mm. in diameter. At a depth of 4 or 5 feet, a few roots were 

 foimd running horizontally, simulating those of the shallower soils. 



