46 Development and Activities of Roots of Crop Plants. 



Table 11. — Average daily evaporations at Lincoln, 1920. 



May 5 to 12 



ex. 



10.5 



June 30 to July 7 



ex. 



May 12 to 19 



14.9 



July 7 to 14 





May 19 to 26 



13.5 



July 14 to 21 





May 26 to June 2 



15.8 



July 21 to 28 





June 2to9 



15.9 



July 28 to Aug. 5 





June 9 to 16 



25.6 



Aug. 5 to 12 





June 16 to 23 



11.3 



Aug. 12 to 19 





June 23 to 30 



19.5 



Aug. 19 to 28 





»A11 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- 







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Fiq. 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 linear 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 



