141 THE STRUCTURE OF ECONOMIC PLANTS 



qualities, which are suited to bread-making, and to its adaptability 

 to a variety of climatic conditions, which has resulted in its being 

 the most widespread of all cultivated forms. For this reason, the 

 following account is based upon T. vulgare unless otherwise stated. 



GENERAL MORPHOLOGY 



The Root System. — The root system is dual, consisting of a 

 primary seminal system and a permanent adventitious one which 



forms a deeply penetrat- 

 ing, widely spread, and 

 profusely branched system 

 of fibrous roots. The pri- 

 mary system typically con- 

 sists of five roots, the tap 

 root and two pairs of lat- 

 erals which arise in the 

 region of the vascular 

 plate of the scutellar node. 

 (Fig. 58.) When a sixth 

 root arises, it occurs at a 

 point near the base of the 

 coleoptile adjacent to the 

 epi blast; and a third pair 

 of rootlets sometimes de- 

 velops at the first inter- 

 node above the second pair 

 and in the same plane with 

 them. All the seminal 

 roots are slender, of uni- 

 form diameter, and pro- 

 duce fine lateral branches. 

 The primary roots do not form a large proportion of the total 

 root system; but, under favorable conditions, they penetrate the 

 soil to a depth of 8 to ii inches or more; and may persist through- 

 out the entire life of the plant. In fact, McCall (9) has pointed 

 out that the subcrown root system is capable of carrying the plant 

 to complete maturity, and Locke and Clark (8) have reported 

 instances under certain arid conditions where the root system con- 

 sisted entirely of seminal roots. In such cases, the plant does not 

 tiller to any extent; and only the main culm develops, which. 



Fig. 58. Stages in the development of the seedling. 

 (After Avery.) 



