THE PLAINS ASSOCIATION. 



65 



below a depth of 18 to 24 inches. Even a rainfall of 2.4 inches in a day 

 had no effect upon the soil moisture below 18 inches. He states that 

 ^'almost the entire root system of short grasses is limited to the sur- 

 face 18 inches," while ''deep-rooted plants are not found here for the 

 reason that at greater depths the soil contains no water available for 

 their use" (1911: 38). The results obtained by the writer in an area 

 of short-grass land locally known as ''adobe" do not correspond with 

 these findings. Careful examination was made of the root systems of 

 Bouteloua gracilis and Muhlenhergia gracillima in pure short-grass land 

 about 25 miles southeast of Colorado Springs (plate 20, a). Here 

 Bouteloua gracilis was dominant with Opuntiapolyacantha, while Muhlen- 

 hergia gracillima was very abundant in matlike areas. Schedonnar dus 

 paniculatus, Senecio aureus ohlanceolatus, Erigeron pumilus, Gutierrezia 

 sarothrce, and Munroa squarrosa were present, but were not at all 

 abundant. In fact, only 15 to 25 per cent of the soil was covered 

 with vegetation. Roots of Bouteloua gracilis were found to be very 

 abundant to a depth of 40 inches, while several roots were traced to a 

 depth of 51 inches. Muhlenhergia gracillima roots were very abun- 

 dant to 50inches, and some reached a depth of 56 inches. 



These findings are so different from those of Shantz that further 

 work seems necessary for a thorough understanding of plains root 

 systems. This also seems to be true for the roots of sandhill species 

 (p. 68). Comparisons of the root habits of these plants with those of 

 other communities are based upon the data made available by these 

 studies, and may need revision when other regions are worked. The 

 great variations of many root systems under different edaphic environ- 

 ments is clearly shown in the section on poly demies (p. 110). However, 

 it is certain that plains plants grow in a soil of low water-content and 

 of very hard texture. The soil in the area where these studies were 

 made consisted of a light-colored loam intermixed with some sand. 

 It is spaded with extreme difficulty and a hand-pick removes it so 

 slowly that in digging the trenches a large pick was kept in constant 

 use. Therefore, roots were unearthed only with great labor. For 

 example, a single specimen of Argemone platyceras occupied the atten- 

 tion of two persons for 1.5 days, while it required the services of a 

 third to do the sketching as the roots were uncovered. At depths 

 varying from 6 to 10 feet a layer of sand occurred. This was in 

 good tilth condition and usually moist enough to hold when pressed 

 firmly into a lump. 



The well-developed system of wide-spreading laterals, so charac- 

 teristic of species of Bouteloua, Gutierrezia, Artemisia, and many others, 

 is undoubtedly a response to the moisture in the surface soil resulting 

 from summer showers. Such roots would be of small advantage to 

 prairie plants in the Pacific Northwest. In the prairies of Nebraska 



