ii8 THE STRUCTURE OF ECONOMIC PLANTS 



scutellum are joined at the level of divergence of the scutellum from 

 the axis and within the embryonic axis are connected directly with the 

 stele. Continuing from the place of attachment of the scutellar bundle 

 to the stele it is easily possible to trace procambial elements to the first 

 leaf above the coleoptile. The vascular system of the coleoptile 

 consists usually of two vascular bundles one on either side. They 

 arise directly from the stele on the embryonic axis, at the upper end 

 of the neck-like interval in the axis already referred to." 



Germination. — In germination, the grain begins to swell, the 

 coleorhiza grows through the pericarp, and is, in turn, penetrated 



H. 



\—pri rt—-\ 



Fig. 45. Stages in the development of the seedling: advrt, adventitious root; colp, coleop- 

 tile; pri rt, primary root. (After Avery.) 



by the primary root, which elongates very rapidly. The coleoptile 

 is pushed upward by the elongation of the first internode, which 

 results from the activity of an intercalary meristem located just 

 below the second or coleoptilar node. This internode differs in 

 this respect from the internodes above it; since, in all others, the 

 intercalary meristems are located near the base. When the coleop- 

 tile has been raised until its base reaches the soil surface, its edges 

 spread apart at the tip and the enclosed foliage leaves begin to 

 emerge. The adventitious roots, arising above the cotyledonary 



