20 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



escaped from cultivation and, because of its prolific seeding and rapid propaga- 

 tion, it has become an important species in natural grassland. It is especially 

 abundant in low prairie and competes successfully with natural vegetation 

 even on the upland. It is confined to the less arid parts of the grassland for- 

 mation. 



The roots of this species have been examined under three sets of eclaphic 

 conditions at Central City and Lincoln, Nebraska. At the former station the 

 plants were growing in a soil of mixed sand and clay overlaid with about 2 

 feet of wind-blown sand. Below the stratum of clay, which had a thickness 

 of 6 feet, almost pure white sand occurred. As at Lincoln, the plants had 

 evidently been in possession of the area for several years. 



The grass spreads by rhizomes, which were somewhat variable as to depth 

 (0.5 to 4 inches), the normal level undoubtedly being more or less disturbed 

 by the movement of the sand. The rootstocks are 1 to 2 mm. in diameter and 

 well branched. The dark-colored, fine, fibrous roots occur in such abundance 

 that with the creeping rootstocks they form a dense, tough sod. Some of the 

 roots have a wide lateral spread, often running nearly parallel with the soil 

 surface at depths of only 0.2 to 0.3 foot for distances of 1 to 1.5 feet from their 

 origin. Usually they run more obliquely or even vertically downward. They 

 completely fill the soil to a depth of about 2.5 feet, below which they are 

 abundant for 2.5 feet more, while a few reach depths of 7 feet. These fine 

 roots are abundantly supplied with hairlike laterals, usually less than an inch 

 in length, but branched and rebranched to the third order. Even the root- 

 tips are well branched with rootlets 1 to 3 inches long. 



The second examination was made in an area of high prairie near Lincoln 

 in a very stiff clay-loam. The upper 1 .2 feet of soil was dark in color and rich 

 in humus. Below this was a subsoil of stiff yellow to slate-colored clay about 

 2 feet thick. This was somewhat intermixed with streaks of decomposed 

 Dakota sandstone which modified its tenacity. Below 3.2 feet the clay 

 became very hard and much jointed, roots being largely confined to these 

 joints. It was intermixed with pockets and streaks of chalk, the latter some- 

 times being an inch in thickness. The soil, especially the deeper portion, was 

 so hard that it was removed with considerable difficulty. Its glacial origin 

 was shown by pebbles often 2 or 3 inches in diameter which occurred through- 

 out, but these were nowhere very abundant. The bluegrass sod was in con- 

 trol of local areas. The greatest root development was in the surface 2 feet of 

 soil, although roots were fairly abundant to a depth of 3.3 feet, while a few 

 penetrated to a maximum depth of 5.8 feet. The wide lateral spread of sur- 

 face rootlets so highly developed in the sand occurred to a much less extent 

 in the clay-loam. 



A third lot of plants was excavated at the low-prairie station, where they 

 were growing in a silt-loam alluvial soil. The working depth was determined 

 at 2.8 feet, although many penetrated deeper, some even reaching a maximum 

 depth of 5 feet (plate b). 



All of these investigations give a greater root depth for Poa than is indicated 

 by the results of King (1893) in Wisconsin (about 2 feet) or Ten Eyck (1904) 

 in Kansas. At the latter station a few roots reached a depth of nearly 4 feet, 

 but at 2 feet the number was small and comparatively few roots extended 

 below a depth of 1.5 feet. It is quite apparent that edaphic conditions greatly 

 modify the root habit, as seen in the plants examined on high prairie, which 

 had a greater depth of penetration than those on the more moist lower areas. 

 The successful competition of bluegrass with native species is probably largely 

 due to its methods of propagation, its massive root system, and dense sod- 

 forming habit. While it requires a fairly moist climate to thrive and it be- 



