ROOT SYSTEMS OF TRUE-PRAIRIE SPECIES. 25 



commonly run off obliquely for at least 1 or 2 inches before turning downward, 

 while still others continue their oblique course until they have extended later- 

 ally 1 to 1.5 feet from the base of the plant. However, these roots, unlike 

 those of many plains species, do not run off in the surface soil. There is ample 

 provision for surface absorption by means of the finer, shorter roots, as well as 

 by numerous branches from the larger ones. These run off in all directions, 

 especially in the first foot of soil, and are branched and rebranched to the third 

 and fourth order. Branching is well developed in the first and second foot, 

 but below this depth laterals are less numerous and more poorly rebranched. 

 In fact, in the third to sixth foot of soil the roots, which are now only a milli- 

 meter or two in diameter, are poorly provided with threadlike laterals, sparsely 

 rebranched, and only 0.5 to 2 inches in length. Three or four roots of each of 

 the plants examined were traced to a depth of about 7 feet; 7.8 feet was the 

 maximum depth recorded for this species. The deeper roots often wander 

 back and forth through small distances, the tips frequently being 1 or 2 feet 

 distant horizontally from the base of the plant. The tips are not well 

 branched. The roots are rather tough, excepi-the younger portions, which are 

 quite brittle. They are tan to white in color, except in the shallow soil, where 

 they are often tinged with red like the base of the stems. Summarizing 

 briefly, we find that the roots are not only deep-seated, but that this species 

 is also fairly well adapted to absorb efficiently in the surface foot of soil, 

 especially below a depth of 4 inches. 



PRAIRIE ROOT SYSTEMS AND PRAIRIE ENVIRONMENT. 



An examination of these data reveals the fact that none of the roots 

 of the prairie species here described are superficial. All extend into 

 the fifth foot of soil, and indeed most of them go a great deal deeper. 

 They afford further evidence for the conclusion already reached, 

 namely, that true-prairie species are provided with well-developed, 

 deep-seated, and extensive root systems. In order to present these 

 facts concisely, all of the prairie species thus far studied (43 in number) 

 are arranged in table 1 into three groups, according to the depth of root 

 penetration. In the first group may be found plants with such shallow 

 roots that they seldom extend below the first 2 feet of soil. These 

 consist entirely of grasses. This group is the smallest and makes up 

 only 14 per cent of the total. The second group is composed of species 

 with roots extending well below the second foot, but seldom deeper 

 than 5 feet. These may be termed intermediate in root depth. Here 

 are to be found 21 per cent of the prairie species. The last and largest 

 list, made up of plants whose roots extend beyond a depth of 5 feet 

 (some to 12 or even 20 feet), includes 65 per cent of the species selected 

 as typical of the prairie flora. 



SUMMARY OF PRAIRIE SPECIES. 



For these species the working depth is also given in table 1. By 

 working depth it is meant to designate the average depth reached by a 

 large number of roots or branches of the root system and to which depth 

 considerable absorption must take place. It has no absolute value 



