WHEAT 



101 



temporary root system. After the plumule unfolds 

 above the ground, the permanent roots start out from a 

 node below the surface. For a short time both the 

 permanent and the temporary roots serve the needs of 

 the young plant, but as the permanent system develops 

 the temporary system withers 

 and dies. The permanent roots 

 increase rapidly in length and 

 develop into a complex fibrous 

 root system, which serves the 

 plant throughout the remainder 

 of its life. The permanent roots 

 branch freely, as many as eight 

 to ten branches being given off 

 from one inch of the main roots. 

 Most of the root system of the 

 wheat plant is in the upper 15 

 to 20 inches of the soil. Below 

 this depth it does not branch 

 freely, but sends long runners 

 down deep into the subsoil. 

 The depth to which the roots 

 will penetrate depends largely 

 upon the physical condition of 

 the subsoil, and upon the loca- 

 tion of the water table during 

 the growing season. In loose 



soils, with the water table several feet below the surface, 

 wheat roots may go down 6 or 7 feet or more. The roots 

 of the permanent system do not vary greatly in diameter, 

 being about the same size their entire length. 



85. The stem or culm. During the early life of the 

 plant the internodes are short, giving at this time the ap- 



FIG. 30. Diagram showing 

 how the plant increases in height 

 by lengthening of the inter- 

 nodes. 



