Introduction. 



5 



have demonstrated a close relation between the vigor of root growth and 

 disease resistance. Where the disease is physiological, resulting from mal- 

 nutrition or insufficient aeration, this relation is at once apparent. It seems 

 certain, in the light of recent investigations, which show the extensive nature 

 of the roots of most crop plants, that the results of many experiments, where 

 plants were grown in pots or even relatively large containers, may have more 

 apparent than real values when the work is repeated under field conditions. 

 A thorough study of root distribution and absorption under cropping condi- 

 tions will throw much light upon the relative value of greenhouse experiments 

 on soil fertility, where containers of various sizes with either surface soil or 

 subsoil were used. Even plant-breeding or crop-production experiments 

 conducted in the field in small adjacent plats or by the row per ear or head 

 method, undoubtedly have been affected and the results in many cases 

 vitiated by the factor of root competition. 



The importance of a thorough investigation of root development and root 

 activities need not be pointed out in greater detail. In preceding volumes 

 (Weaver, 1919, 1920) the relation of a knowledge of root systems to plant 

 production in its broader sense has been emphasized. The underground 

 parts of 1,500 native plants of forest, chaparral, sandhills, plains, and prairie 

 have been studied with a view to acquiring fundamental knowledge of value 

 in the solution of many problems of crop production. Outstanding among 

 these are range management and improvement, involving that complex 

 phenomenon termed plant succession; afforestation and reforestation; and 

 indeed the whole problem of land classification based upon indicator signifi- 

 cance of native vegetation. Such studies through an extended region, such 

 as our grassland formation, afford an excellent background for investigations 

 of crop plants grown in any part of the area. For a knowledge of root posi- 

 tion of native plants, especially when interpreted in their community rela- 

 tions, so clearly reflects the moisture conditions of the soil that it aids not 

 only in selecting the kind of crop to be most profitably grown, but also helps 

 in determining the proper methods of tillage. This is especially true when 

 the root habits of crop plants are also known and the degree to which they 

 are modified by the environment. An extended study of the root systems of 

 cereals from the Missouri to the Rocky Mountains has been reported and 

 their growth habits correlated with the environment as indicated by the 

 native vegetation. Moreover, the variations of root development of many 

 species of crop plants on upland and lowland have been worked out in a 

 preliminary manner (Weaver, 1920). 



This book may be considered a continuation of "Root Development in the 

 Grassland Formation.' ' The investigations here recorded were carried out 

 during the growing-seasons of 1919 to 1921. Stations were selected at Peru 

 and Lincoln, Nebraska, at Phillipsburg, Kansas, and at Burlington, Colorado. 

 These stations have a mean annual precipitation of about 33, 28, 23, and 17 

 inches, respectively. The differences in climate are clearly expressed in the 

 type of natural vegetation. The true prairies at Lincoln give way southeast- 

 ward along the Missouri near Peru to the subclimax prairie, which is poten- 

 tially chaparral or woodland, the grasses having possession only because of 

 such disturbances as grazing, fire, mowing, etc. At Burlington, in eastern 

 Colorado, a typical expression of the short-grass plains is found, while in 



