ECADS. 93 



was in some respects rather exceptional. Either some of the plants 

 excavated had not reached their maximum root extension or the deeper 

 soil was much drier than is usual in the sandhills further eastward in 

 Colorado and in Nebraska. This is an excellent illustration of the 

 value of a broader field for study and the need of extensive ecological 

 investigations before correct conclusions may be drawn. It is felt that 

 the present broad survey supplies this need regarding the root habits 

 of grassland vegetation. 



Among mixed-prairie species on hard lands, only 4, including 2 cacti, 

 are rather superficially rooted; 16 species are of moderate depth (2 to 5 

 feet), and of these only 3 are poorly equipped to carry on surface ab- 

 sorption. A group of an equal number of species, including 3 grasses, 

 has roots which extend well below the fifth foot of soil, and many in 

 fact to a depth of 7 to 9 feet. Of this number, 7 are adapted for absorp- 

 tion in soils mostly below the surface foot or two only. Thus 11 per 

 cent of the mixed-prairie species of hard lands are shallow-rooted, 28 

 per cent have little or no provision for surface absorption, while 61 per 

 cent are both fairly deep-rooted and well adapted to absorb water even 

 when the surface soil only is moist. 



In a comparison of mixed-prairie species of sandhills and hard land, 

 the only marked difference as a group is the somewhat better develop- 

 ment of the root system in the former habitat, especially as regards 

 smaller absorbing rootlets. Indeed, the excellent development of 

 surface absorbing laterals is equaled only by certain short-grass plains 

 species. The general similarity in the root habit as regards position 

 in the soil and depth of penetration of short-grass and mixed-prairie 

 species is so marked that experimental studies now under way on the 

 competition of the several dominants of the two grassland associations 

 should throw much light upon the general problem of succession, and 

 especially the causes of the present distribution of grassland dominants. 



In a comparison of the root habits of plants in these three drier 

 grassland habitats with those of true prairie, two characters stand out 

 rather strikingly. In true-prairie species, probably due to a more 

 constant supply of water in the subsoil, the roots as a group do not 

 spread so widely in the surface soil. Also, the depth at which the 

 largest number of absorbing roots are found is usually greater. This 

 condition is likewise clearly reflected in the root habits of cereal-crop 

 plants (cf. Chapter VI). 



In seeking a correlation of the root habit of plants of true prairies, 

 of mixed prairie covering sandhills and hard lands, and of short-grass 

 plains, with their respective environments, several ecological factors 

 must be considered. The most important of these are water-content, 

 aeration, soil temperature, texture, and chemical composition. An 

 examination of the literature emphasizes the fact that relatively little 

 work has been done either upon an intensive study of root systems or 



