150 Physics of the Soil. 



ward and wedged sidewise, setting the soil aside and thus 

 making room for itself. The root cap does not slide for- 

 ward past soil grains but is anchored rigidly to them ; the 

 tip entering existing cavities is enlarged by growing for- 

 ward under and through the cap, the rear cells of which die 

 after the root has grown past them, the root cap being a sort 

 of point continually renewed as the root advances. 



183. The Extent of Root Development of Corn. It is only 

 by careful study that the extent of root development in a 

 soil can be learned. In Figs. 48 and 49 are shown the 

 amount and distribution of corn roots at two stages of 

 growth. When the corn was 30 inches high the whole of 

 the soil to a depth of two feet was as full of roots as the 

 engraving shows between the two hills ; when the corn was 

 coming into tassel the roots had penetrated to a depth of 

 three feet and had come closer to the surface ; and at ma- 

 turity the roots had reached four feet in depth, making 

 their way through a fairly heavy clay loam and clay sub- 

 soil, the fourth foot only being sandy. 



It should be understood that the roots here shown grew 

 in undisturbed field soil and were obtained by going into 

 the field at the stage of growth shown and digging a trench 

 around a block of soil a foot through and the length of the 

 width of the row. The cage was then set down over the 

 block ; wires run through the block of soil to hold the roots 

 in place and then the soil washed away by pumping water 

 in a fine spray upon the block. Three days' work for two 

 men were required to secure the sample in Fig. 49. 



184. Extent of Root Development of Grain. In Fig. 50 

 is represented the depth to which the roots of winter wheat, 

 barley and oats penetrated a heavy clay soil and subsoil. 

 The roots are what were found in a cylinder of soil just 

 one foot in diameter and were obtained by driving a cylin- 

 der of metal four feet long its full depth into the soil and 

 then washing the dirt out of it. It will be seen that in each 

 case the roots have reached a depth of fully four feet. 



