ROOT SYSTEMS OF TRUE-PRAIRIE SPECIES. 



35 



effect is a limitation in the development of both root and shoot of winter 

 annuals (Cannon, 1911:88). With such superficially rooted species 

 as Opuntia polyacantha and 0. camanchica, abundant both in the short- 

 grass plains and mixed prairie, as indeed with all persistent portions of 

 perennial roots in the surface soil, the seasonal changes in soil tempera- 

 ture must be extreme. Soil temperature, like soil aeration, affects the 

 development of root systems not only directly, but also plays a part 

 in the life activities of soil microorganisms. These, as conditioned 

 by soil temperature, may affect the plants directly (Jones, 1917) or 

 alter the chemical composition of the soil and thus influence the root 

 environment, which in turn may modify its development. Thus, soil 

 temperature as an ecological factor is clearly of much importance 

 and warrants careful study. 



Fig. 11. 

 A meter quadrat in the true- 

 prairie community at the 

 upland station at Lincoln, 

 Nebraska. A, Andropo- 

 gon scoparius; Af , Andro- 

 pogonfurcatus; Al, Allium 

 mutabile; Am, Amorpha 

 canescens; An, Andropo- 

 gon nutans; At, Aster 

 multiflorus; B, Bouteloua 

 gracilis; Be, Bouteloua 

 curtipendula; C, Carex 

 pennsylvanica; E, Eu- 

 phorbia serpens; F, Fes- 

 tuca octoflora; K, Kceleria 

 cristata; L, Linum sul- 

 catum; Le, Lepidium 

 virignicum; Li, Liatris 

 punctata; O, Oxalis stricta; 

 P, Poa pratensis; Pa, Pa- 

 nicum scribnerianum; S, 

 Stipa spar tea; So, Soli- 

 dago missouriensis; V, 

 Viola pedatifida. 



Summarizing, these combined differences of lower rainfall, drier soil, 

 greater evaporating power of the air, and less favorable temperatures 

 for growth at the mixed-prairie station are reflected both in the vegeta- 

 tional cover and in the root habit. Figure 10 shows a meter quadrat 

 of the vegetation at the station in the mixed prairie (plate 4, a). In 

 figure 11 is shown a similar area from the upland-prairie station at 

 Lincoln (plate 4, b). Although these are limited areas when consid- 

 ering the vegetation as a whole, still the fact remains that a few care- 

 fully selected quadrats well made and thoroughly studied reveal much 

 more concerning the structure of vegetation than long lists of species. 

 In fact, the more exact quadrat method necessitates considerable 

 familiarity with the vegetation. 



