46 



Development and Activities of Roots of Crop Plants. 



Table 11. — Average daily evaporation,^ at Lincoln, 1920. 



May 5 to 12 10.5 



May 12 to 19 14.9 



May 19 to 26 13.5 



May 26 to June 2 15.8 



June 2 to 9 15.9 



June 9 to 16 25.6 



June 16 to 23 11. 3 



June 23 to 30 19.6 



June 30 to July 7 13 . 2 



July 7 to 14 13.8 



July 14 to 21 19.1 



July 21 to 28 18.7 



July 28 to Aug. 5 19.3 



Aug. 5 to 12 20.7 



Aug. 12 to 19 16.3 



Aug. 19 to 28 9.6 



'All atmometers, exept those at Peru, were equipped with the non-absorbing device. 



The roots had attained a maximum lateral spread of 0.8 foot, and a work- 

 ing depth of 2.3 feet, while a few reached a maximum depth of 4.1 feet. A 

 comparison of figures 19 and 21 a shows that the chief difference between 

 the older root system and the younger, aside from greater length growth of 

 most of the roots, is one of increase in number and branching of laterals. 

 In fact, at the early stage (May 30), the general area to be occupied by the 

 mature root system was well blocked out. Later it had been increased some- 



April 



21 29 



May 



12 19 



June 



July 



16 2 3 30 



14 21 2S 



August 



12 19 26 



80 



65 



55 



Fig. 20. — Average daily air-temperature (long broken lines), soil-temperature (short 

 broken lines), and humidity (solid line), 1920. 



what in width and considerably in depth, but especially it had come to be 

 occupied much more thoroughly in all parts by a fine network of delicate 

 roots. In the surface foot of soil, 7 to 10 laterals, and sometimes as many 

 as 15 to 18, occurred on a single Hnear inch. On the scale to which the draw- 

 ings were made it was very difficult to show all of the multitude of rootlets. 

 The laterals were mostly 1 to 2 inches long, infrequently 3 to 5 inches, and 

 were furnished only poorly with secondary branches. Branchlets of the 



