62 Development and Activities of Roots of Crop Plants. 



heavy rains three days were required for the water to penetrate to a depth 

 greater than 6 inches. This high run-off has been repeatedly confirmed by 

 the writers while the penetration of water, when applied to moisten the sur- 

 face soil prior to root examinations, was exceedingly slow. The excellent 

 root development of native plants in the surface 1.5 to 2.5 feet of soil fits them 

 to absorb the water readily, and they help to prevent deep water penetration 

 (Weaver, 1919, 1920). This is of especial significance in this study, since 

 cultivated plants modify their root distribution in a manner similar to that 

 of the native vegetation. 



Table 16. — Chemical analyses of soils from Burlington.* 







Depth of sample in 



feet. 





0.0 to 0.5 



0.5 to 1.0 



1 to 2 



2 to 3 



3 to 4 





p. ct. 



p. ct. 



p. ct. 



p. ct. 



p. ct. 





none 



none 



none 



none 



none 



Carbon dioxide 



0.03 



0.30 



1.71 



2.10 



2.60 





4.67 



3.13 



3.11 



3.34 



2.84 



Phosphorus pentoxide .... 



0.189 



0.504 



0.428 



0.406 



0.525 



Sulphur trioxide 



0.007 



0.017 



0.006 



0.006 



0.005 



Potassium oxide 



2.32 



2.39 



2.45 



2.51 



2.22 





0.184 



0.130 



0.101 



0.086 



0.084 



1 Methods used were the same as described on p. 32. 



The field in which the crop plats were located was a portion of a vast level 

 tract surrounded on three sides by fields of wheat, corn, and Sudan grass, 

 respectively. The sod had been broken in the spring of 1918 and planted to 

 Sudan grass. After this was harvested the ground was plowed late in the 

 fall, and the next spring it was repeatedly harrowed and a good seed-bed 

 formed before the experimental crops were hoed in. 



Wheat, Triticum ^estivum. 



On June 12, 58 days after planting, the Marquis Spring wheat was thor- 

 oughly examined. The plants averaged 10 inches in height, the tallest 

 reaching 12 inches. They were well-tillered, many having from 4 to 8 

 shoots. The parent plants had an average of about 6 leaves each. Many of 

 the tillers were 6 to 10 inches high, but others were only 1 or 2 inches. The 

 wheat was somewhat fired at the base and many of the younger tillers were 

 dead and dry, as were also the two or three basal leaves on the larger tillers 

 and parent plants. However, a part of this injury was the effect of frost. 

 The stand, like that of the other cereals, was thin but fairly even, germination 

 having occurred under rather favorable moisture conditions. On April 15, 

 at the time of planting, more than 10 per cent of available moisture was 

 found in the surface foot of soil (table 17). Although soil samples were not 

 taken again until June 3, it seems clear from the rainfall records that mois- 

 ture conditions were quite favorable, at least until the latter part of May. 

 During the last half of April a total of 1.4 inches of rain fell at four well- 

 distributed intervals, while from May 1 to 15, four other favorably distrib- 



