68 Development and Activities of Roots of Crop Plants. 



This may have been due in part to the smaller number of plants supported 

 by the oat roots. Compared with growth in more humid regions, the roots, 

 while less extensive, were much more profoundly branched. Many young 

 roots which had originated near the surface and were densely woolly with 

 root-hairs, had dried out and died after reaching a length of only 0.3 to 3 

 inches. This fact leads one to believe that the excellent development 

 of long, rebranched laterals, especially in the surface 1.5 feet of soil, may be 

 correlated not only with the prevailing relatively low water-content, but 

 also with the lack of ability on the part of the plant to produce new absorbing 

 organs in the dry surface-soils. 



On July 7, when the oats had reached a height of 1.5 feet (maximum 1.8 

 feet) and were in the dough stage, roots were again examined. The crop 

 had been somewhat damaged by grasshoppers, but the grain was well filled 

 and of good quality when harvested July 19. In making the excavation 

 preliminary to root study, a very dry hardpan was encountered at a depth 

 of 2.7 feet. It had a thickness of about 1.3 feet. Below this stratum the 

 soil was mellow and powdery. Roots were quite abundant to the hardpan 

 layer, and the working depth reached approximately this level. As in the 

 case of wheat, the surface soil was also completely filled with exceedingly well 

 branched roots, these apparently being a response to available water-content 

 furnished by summer showers. The lateral spread of roots was about 10 

 to 11 inches. This root habit is markedly different from that of plants 

 grown from the same seed in more moist soil and in a less arid climate (cf. 

 figs. 21 a and 30). 



Barley, Hordeum vulgare. 



Barley was examined also on June 12. The plants were about 11 inches in 

 height, the tallest exceeding this by only 2 inches. The number of tillers 

 varied from 2 to 6 and averaged 3 or 4 per plant. 



The working depth of the barley roots was determined at 2 feet; a few 

 penetrated 4 to 6 inches deeper. The general root habit was very similar 

 to that of wheat, the lateral spread being slightly less. In the surface 6 

 inches of soil the primary branches were 2 to 3 inches long, the secondary 

 ones 0.3 to 0.5 inch, and all were densely hairy. On one root, at a depth of 

 4 inches, 58 primary laterals were counted on a segment of root only 2 inches 

 long. These had an average length of about 1 inch and were fairly well 

 supplied with secondary branchlets. On another root, at a depth of 5 inches, 

 26 branches occurred on a segment an inch in length. These cases well 

 illustrate the profound root development in the first foot of soil. As already 

 described for wheat and oats, numerous young roots from 0.3 to 3 inches long 

 had died. These superficial roots must have had their origin during a time 

 when moist soil prevailed; they were densely covered with root-hairs. As 

 a whole, barley roots, like those of oats, are scarcely as well-developed as are 

 those of wheat. 



By June 25 the barley was nearly all headed out. The crop was somewhat 

 damaged by grasshoppers. On July 7, when the root system was again 

 studied, it was in the dough stage. The plants averaged 1.7 feet in height, 

 with a maximum height of 2 feet. An average of 254 stalks were counted 

 in selected square meters. The tillers averaged only one per plant, many 

 having dried out and died. The roots extended even more widely in the 



