THE ROOT SYSTEMS OF CEREALS. 



125 



given on the percentage basis in tajsle 12, where growth in the true 

 prairie is considered unity. It may be noted that rye shows the 

 greatest extremes in height of tops, and wheat in root-depth, in the three 

 communities, while oats show the least. General correlations between 

 precipitation and plant association are apparent in every case. 



Table 12. — Relative development of cereal-crop plants 1 and relative precipitation in the several 



grassland associations. 



Rye: 



Height of tops 



Working depth 



Maximum depth 



Oats: 



Height of tops 



Working depth 



Maximum depth 



Wheat: 



Height of tops 



Working depth 



Maximum depth 



Mean annual precipitation 



Precipitation from July 1918 to July 1919 

 Precipitation from January to July 1919.. 



Short-grass 

 plains. 



56 

 69 

 65 



85 

 79 



64 

 61 

 51 

 58 

 73 

 50 



Mixed 

 prairie. 



66 

 92 

 90 



94 

 95 

 94 



85 

 93 

 80 

 64 

 77 

 53 



True 

 prairie. 



100 

 100 

 100 



100 

 100 

 100 



100 

 100 

 100 

 100 

 100 

 100 



1 In order to secure greater accuracy in percentages, these results were obtained directly from 

 the field notes of root depths given in feet and inches. Table 10 gives the measurements to the 

 nearest tenth of a foot. 



These data, which agree with those of other investigators, emphasize 

 the depth at which crop plants distribute their roots, when grown under 

 favorable climatic conditions as indicated by true prairies, where the 

 subsoil is moist. Such studies must lead to a revision of the current 

 ideas of the depths at which crop plants carry on absorption, especially 

 when nearing maturity (cf. p. 139). The smaller development of both 

 aerial and underground portions of crop plants in mixed prairie and 

 their still poorer development in the short-grass plains is to be expected, 

 but the correlation has not heretofore been worked out. Shantz (1911) 

 has given certain correlations between root development of native 

 species and water-content as affected by soil type in eastern Colorado, 

 but his findings of root-depths in short-grass lands appear quite erron- 

 eous. The close correlation between the poorer development of root 

 and shoot of a given crop as less favorable growth conditions occur is 

 marked. Such a relation has also been found for Agropyrum glauctim 

 (p. 78). These results greatly increase the exactness of the use of 

 natural vegetation as indicators and throw much light upon agricul- 

 tural practice. 



