64 



Developtfwnt and Activities of Roots of Crop Plonis. 



was that of wheat grown at Lincoln. The primary laterals varied in length 

 from 0.3 to 3.0 inches, frequently as many as 20 to 27 branches occurring on 

 a single inch. Secondary laterals, 0.2 to about 0.5 inch in length, were nu- 

 merous. Even the root-ends were well-branched with rather long laterals 

 (fig. 27). Thus the root system, although largely confined to the surface 

 2 feet of soil, because of its wide lateral spread and profuse branching, was 

 well adapted to extract water and solutes from these soils of low water- 

 content. The roots in the surface 6 or 8 inches were not at all fleshy, but 

 tough and wiry, and many were at this time drying out. 



A final examination of wheat was made on July 7, when the plants were 83 

 days old. They had fully headed out by June 25, and were now in the dough 

 stage. The crop averaged 1.7 feet in height, with a maximum height of 1.8 

 feet. The plants were thin on the ground, and many had no tillers, while 



Fig. 27. — Wheat roots showing normal differences in branch- 

 ing at Lincoln, L, and Burlington, B. 1, at 

 depth of 1.5 feet; 2, root-ends. 



some showed 4 to 6 tillers, but the average total number of stalks in selected 

 meter quadrats was only 201. Most of these did not head out (plate 2 a). 

 When harvested on July 19, the heads were well filled and the grain was of 

 fair quality. 



The interval since the last examination on June 12 was one of scant water- 

 supply and high evaporation. Rain fell on 11 days, but only 4 showers of 

 more than 0.2 inch occurred, heavy rains falling on June 18 (1.35 inches) 

 and on July 5 (0.45 inch). A glance at the water-content of the soil given 

 in table 17 is sufficient to show the prevailing drought. During the latter 

 part of the period the crops ripened and dried rapidly. Three days after 

 the 0.45-inch rain, on July 5, no water was available in the surface 2 feet of 

 soil. Although samples for water-content determinations were taken as 

 usual in duplicate, local differences in soil-structure caused rather noticeable 

 differences in run-off and penetration in closely adjacent areas in the same 



