70 Development and Activities of Roots of Crop Plants. 



the necessary supply of water, which occurred in limited amounts and was 

 confined here to the surface 2 or 2.3 feet of soil. Chemical analyses (table 

 16) show that the soil is rich in all the necessary nutrients. Nodules occurred 

 on the roots at all levels. Aeration could not have been a limiting factor to 

 growth in this dry soil, and undoubtedly water played the dominant r61e. 

 This conclusion is substantiated by further studies. 



A final examination was made on August 25. The water-content (table 17) 

 was rather uniformly low; however, determinations were made only at lather 

 long intervals. Showers of 0.86 inch occurred July 16 and 17; 1.26 inches of 

 rain fell on July 26; and 1.34 inches early in August; while a drought period 

 of 15 days' duration was broken by 0.72 inch of rainfall on August 20. 

 Although the crop was often in a semiwilted or wilted condition during the 

 periods of stress (figs. 28 and 29 and table 18), when more favorable conditions 

 occurred growth was resumed. Thus, by August 25 the plants had increased 

 6 inches in height since July 7, the tallest reaching 11 inches. They had 

 blossomed and most of the flowers had dried. 



In the new trench, which was not far from the former ones, the haidpan 

 came to within 2 feet of the surface. This layey delimited the depth of root 

 penetration and none was found deeper. The tap-roots were 3 or 4 mm. or 

 less in diameter. They were profusely branched with both large and small 

 laterals. Not infrequently some of the laterals were equal in size to the tap. 

 Many spread at various depths almost parallel with the soil surface or obliqued 

 downward, reaching distances of 1 to 1.5 feet, horizontally from the tap. 

 Some were found with a maximum lateral spread of 1.5 to 2 feet. Small 

 branches were numerous. The soil was remarkably well occupied by the 

 network of roots, a condition quite unusual in fields of young alfalfa of more 

 humid regions (c/. figs. 25 a and 31). 



Sweet Clover, Melilotus alba. 



The first examination of the root development of sweet clover was made 

 on June 11, when the plants were 57 days old. They averaged 3 inches 

 in height, although some were an inch taller. The stand was quite good. 

 The tops were beginning to branch and the crop was in fairly good condi- 

 tion, except, as a result of drought, many of the leaves on some plants were 

 partly wilted and folded during the hotter portion of the day. Not a few 

 of the roots reached a maximum depth of 2.3 feet, and one, following the 

 course of a large decayed Sudan-grass root, penetrated a foot deeper. The 

 working depth was about 2.0 feet. The roots were mostly much smaller in 

 diameter, especially in the dry surface 6 inches of soil, than those at Lincoln, 

 but the root development as regards number, branching, and lateral spread 

 was almost identical with the latter. In the deeper soil, however, branching 

 was much better developed. Considerable variation occurred in regard to 

 abundance of laterals near the tip. On some plants as many as 15 branches 

 about 0.2 inch long occurred on a single inch of tap-root, while on others they 

 were scarce. Numerous counts as regards number of primary and secondary 

 branches showed that they were not only more abundant, but also averaged 

 longer than those in the more humid soil eastward. 



By July 7 the crop had reached a height of about 5 inches, although some 

 especially well-developed plants were 8 inches tall. The more thrifty appear- 



