6 



THE ECOLOGICAL RELATIONS OF ROOTS. 



many of them breaking up at this depth into clusters of small branches. The 

 roots are slightly reddish in color. The branching is characteristic but difficult 

 to describe. 



Stipa spartea. — This perennial grass is one of the dominants in the prairies, 

 being especially conspicuous during the month of June, when it gives tone to 

 the estival aspect. Its root system is rather meager when compared with 

 most of the other prairie grasses. Strong fibrous roots from 1 to 1.5 mm. in 

 diameter descend rather vertically into the soil to a maximum depth of only 

 21 to 26 inches (plate 4, b). A few spread laterally in a diagonal direction to 

 a distance as great as 10 or 12 inches. Numerous smaller roots fill the surface 

 soil, while the larger ones send off many laterals to a depth of about 14 inches, 

 where the main roots may break up into many fine branches. The hairy 

 cortex causes the soil to cHng to it very closely. This pulpy cortex has a 

 grayish-white color and peels off very easily, leaving a very wiry, tough stele . 



Koeleria cristata. — ^Whether on the prairies of Minnesota or Nebraska or 

 in the Pacific Northwest, Koeleria is an important grass in the estival aspect. 

 As in the case of Stipa spartea, which also makes a rapid growth and blossoms 

 early, the vegetative and reproductive activity may be correlated with the 

 shallow root system. In eastern Washington, where Koeleria is a common 

 bunchgrass, it flowers in late June, soon dries up, and remains dormant until 

 revived by the autumn rains. In this region the deepest root found was at 

 28 inches, and 15 inches was determined as the average depth (Weaver, 1915). 



This plant has a very shallow but exceedingly well-developed root system. 

 None of the roots of the 7 plants examined reached depths of over 21 inches, 

 while the average root depth was about 15 inches (plate 5, a). A great abun- 

 dance of fine rootlets spread out from the base of the plant and occupy the 

 soil exclusively for a distance of 8 inches on each side of it. Indeed, some of 

 the roots run almost horizontally and are less than 0.5 inch deep in the soil. 

 The roots are yellowish-brown in color, usually less than 0.2 mm. in diameter, 

 and branch and rebranch to form a dense mat. 



Elymus canadensis. — This plant is an important prairie species of wide 

 distribution. Like Koeleria, it is comparatively shallow-rooted, but has a 

 widely spreading root system. Five plants in loess soil gave maximum root 

 depths of 16, 17, 20, 21, and 22 inches respectively. Plate 5, b, shows the 

 rather meager root development when compared with most of the other 

 grasses. The obliquely running roots reach distances of 20 inches or more 

 on either side of the base of the plant. Lateral rootlets are seldom over 2 

 inches long and may branch to the third or fourth order. The roots are white 

 in color and from 0.1 to 0.5 mm. in diameter. They are very tough and wiry. 



Agropyrum repens. — From the extensive rhizomes of this perennial, which 

 are often 2 to 3 feet long, arise numerous fine, silvery-white roots. These 

 send off rather poorly branched laterals as they descend somewhat vertically- 

 downward, some to a maximum depth of 8 feet. The first 30 inches of soil 

 is abundantly filled with roots, while many penetrate to a distance of 4 to 7 

 feet. Many of the roots of the 10 plants examined pursued a peculiar zigzag 

 course, a character which was more pronounced in the deeper roots. 



Distichlis spicata. — This low, dioecious perennial of seacoasts and alkaline 

 soils is still quite abundant on the ''salt flats'' about Lincoln, although it is 

 being replaced by other species as the soil becomes less salty, due to better 

 drainage resulting from the straightening of stream courses. It has consider- 

 able forage value throughout the West, where it occurs abundantly in low 

 saline situations. About Lincoln most of the area occupied by salt grass is 



