TRITICUM 143 



though reduced in size, is normal but tends to lodge, owing to 

 the absence of the support usually afforded by crown roots. 



The permanent root system is comprised of whorls of adventitious 

 roots which arise from the lower nodal regions of the main stem 

 and its branches near the soil level. The first adventitious roots 

 appear at the tillering node about an inch below the soil level, and 

 consist of a pair of roots arising at right angles to the plane of 

 phyllotaxy and parallel to the plane of the three pairs of seminal 

 roots. Another pair is formed at the second node in similar man- 

 ner; but, near the ground level, where the internodes are longer, 

 the whorls may consist of four to six roots arranged in pairs. Each 

 secondary axis produces its adventitious system in a manner similar 

 to that of the main culm, except that a single root instead of a pair 

 is usually produced at the base of each secondary or subsequent 

 lateral axis. 



The rapidity and extent of development of the adventitious 

 roots vary with cultural conditions and practice. Weaver (15) 

 has investigated this point; and finds that, under favorable con- 

 ditions, root elongation is very rapid, being maintained in some 

 cases at the rate of half an inch a day for 60 or 70 days in winter 

 wheat. In describing the root system of spring wheat, he states, 



"The roots of the secondary system ramify the soil near the surface 

 6 to 9 inches on all sides, and likewise fill the x to 3 feet below this 

 area with a network of well-branched roots. Winter varieties are 

 similar in general habit but more deeply rooted. Crops planted early 

 during seasons favorable for growth form a secondary root system 

 which rather thoroughly fills the surface 12. to 1.0 inches of soil, while 

 the primary roots extend well into the third and fourth foot. The 

 mature root system has a working level of 3.5 to 4 feet and a maximum 

 depth of 5 to 7 feet." 



The degree of branching and depth of penetration are subject to 

 great modification, depending upon the type of the subsoil, the 

 amount of moisture and aeration, and the character of the fertilizer 

 applied to the soil. (Fig. 59.) 



The Stem. — The jointed, cylindrical stems or culms are smooth 

 or scabrous, and contracted at the nodes, which are solid. The 

 internodal portions are hollow at maturity, except in some varieties 

 of macaroni and poulard wheats in which there is a persistent pith. 

 The total height may vary from x to 5 feet, being even shorter in 

 some of the dry land areas; and there are usually about six inter- 



