ROOT SYSTEMS OF MIXED-PRAIRIE SPECIES. 67 



Other common species are Opuntiafragilis, Senecio aureus oblanceolatus, 

 Erigeron ccespitosus, and Coreopsis tincloria. 



Throughout northwestern Kebraska and western South Dakota 

 some fine mixed prairies occur. On the uplands at Ardmore, Agropy- 

 rum glaucum reaches a height of over 2 feet, while the flowering stalks 

 of Bouteloua gracilis have a length of 12 inches, both indicating very 

 favorable growth conditions. The rainfall is somewhat greater (17.8 

 inches) than at either of the preceding stations. Evaporation is prob- 

 ably much lower and may be an important factor. Although the 

 run-off must be high, the Pierre clay soil is very retentive of water. 



Besides the wheat-grass, Stipa comata, Aristida purpurea, Poa shel- 

 doni, Bouteloua curtipendula, and Andropogon scoparius are tall-grass 

 dominants. The layer of Bulbilis dactyloides, Bouteloua gracilis, 

 Carex stenophylla, C. filifolia, and Festuca octoflora is well developed 

 (plate 3, a, b). Besides the grasses, of which the dominant species 

 alone are here recorded, the presence of numerous societies is indicative 

 of the rather favorable climatic conditions. Some of the more im- 

 portant of these are Psoralea tenuiflora, P. argophylla, Artemisia 

 frigida, Opuntia polyacantha, Astragalus drummondii, Aragallus lam- 

 bertii, Malvastrum coccineum , Plantago purshii, and Grindelia squarrosa. 

 In these mixed prairies the following plants were examined: 



Bouteloua curtipendula. — This species of grama has a wide range and con- 

 siderable forage value. Although it seldom occurs in pure growth in the 

 areas under consideration, it is nearly always present in true prairie vegetation 

 and is often of considerable abundance in mixed prairies also. It normally 

 grows in tufts or bunches, but under certain conditions forms a good sod. A 

 number of fine specimens were examined in the mixed prairie near the base 

 station at Colorado Springs. Like most prairie grasses, it propagates by 

 rhizomes. These are 1 to 2 mm. in diameter and usually not over 2 to 6 inches 

 n length. From the base of the clumps, as well as from these rhizomes, there 

 iarise great numbers of roots, the largest of which are seldom over a millimeter 

 in diameter (plate 13, b) . Many of these run off more or less parallel with the 

 soil surface and at a depth of only 2 to 4 inches. In this manner they reach 

 out to a distance of 1 to 1.5 feet from the base of the plant before turning 

 downward. This root habit is very characteristic of most grasses of mixed 

 prairies and short-grass plains. Many other roots pursue a course more 

 obliquely downward, reaching the working depth of 4 feet at a horizontal 

 distance of only 8 to 10 inches from the base of the clump. Still others extend 

 more or less vertically downward, some reaching a maximum depth of 5.5 feet. 

 Below this depth none was found, although the walls of the trench were 

 undercut to a depth of 7 feet. All of the roots are abundantly supplied with 

 delicate rebranched laterals not unlike those of Bouteloua gracilis. They arc 

 especially well-developed in the surface 2 feet of soil, which is in fact literally 

 filled with them. The main branches are 1 to 3 inches in length and their 

 laterals, while only about an inch long, are exceedingly well furnished with 

 almost microscopic rootlets only a few millimeters in extent. Below 2.5 feet 

 the roots are much less abundant and the branches are much shorter. How- 

 ever, the roots are quite abundant to 4 feet, the working depth, while only a 

 few extend to the maximum depth of 5.5 feet. 



