40 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



fully removed from the roots in the trench-wall along the edge of the 

 quadrat to a horizontal distance of 3 inches. While this is under way 

 the roots are measured and drawn in position to scale. This gives a 

 picture of the exact root distribution in a block of soil a meter long, 3 

 inches wide, and to the depth of root penetration. Dotted lines indi- 

 cate the entry or exit of roots into or from this soil area, respectively. 

 In this way it is possible to show both the lateral and downward ex- 

 tent of the roots, the area occupied by each, and to get a picture of 

 their interrelations. In the case of prairie grasses, however, it is not 

 possible to picture all of the roots, as they are so numerous that this 

 would confuse the situation and thus defeat the very purpose of the 

 bisect. 



A glance at plate A reveals the great masses of roots which fill the 

 surface 3 or 4 feet of soil and the intense competition for water and 

 solutes which must result. If the first impression is one of a confusion 

 of details, this will only emphasize the difficulties met in the excavation 

 of roots. It requires a very great amount of the most careful, painstak- 

 ing effort, and repeated study under many conditions, until methods 

 have been developed and a sufficient technique has been acquired so 

 that one may become quite as familiar with the root systems as the 

 aerial parts. However, a study of this plate shows that the root systems 

 of the different species form Layers in the soil. In fact, three of these 

 layers are quite evident. The first extends to a level of about 2 feet, 

 where the roots of Stipa spartea, Kceleria cristata, and Carex pennsyl- 

 vanica mostly terminate. A second layer, extending to a depth of 

 about 5 feet, is dominated by Andropogon furcatus, Bouteloua gracilis, 

 and B. curtipendula. Extending far below this level, and extracting 

 much water from the deeper soil, are Liatris punctata, Aster multi- 

 florus, Solidago missouriensis, and Amorpha canescens. In this group 

 of species none is well fitted for much absorption in the surface soil. 

 In fact, there is little or no direct competition between these plants and 

 those enumerated in the first group. Such a root distribution, together 

 with maximum activities above ground at different times of the year 

 (resulting in seasonal aspects), makes it very clear how so many plants 

 can not only live but show normal development in such limited sur- 

 face areas, e. g., 215 individuals or individual groups in a single 

 square meter. 



The bisect along the edge of the quadrat (fig. 13) at the low-prairie 

 station is shown in plate B. Here many of the plants are coarser 

 rooted, especially Spartina cynosuroides, Panicum virgatum., and Andro- 

 pogon furcatus. Three root layers are more or less apparent, the upper 

 one being demarked by Poa pratensis, the second by Andropogon 

 furcatus, while all of the other species extend well below the 5.5-foot 

 level, beyond which depth the roots of Andropogon do not reach. In 

 fact, the root systems of several species excavated on both high and 



