124 THE STRUCTURE OF ECONOMIC PLANTS 



in the cortex below the coleoptilar node." A bud is seldom dif- 

 ferentiated in the axil of the coleoptile. Stomata are found only 

 in the outer epidermis and usually occur in rows on either side of 

 the vascular bundles. 



-0 ep 



- - chl par 



ph 



'- -xy 



Fig. 49. Transection of a portion of the coleoptile showing coleoptilar bundle: chl par, 

 chlorophyll parenchymai ep, outer epidermis; ph, phloem; xj>, xylem. (After Avery.) 



Second Internode. — The second internode is also transitional. 

 (Fig. 50.) It is less root-like than the first internode, but lacks the 

 definite meristelic structure of the higher internodes. The cortex 

 is relatively thick, and centrad to it there is a meristematic zone of 

 tissue which is probably of pericyclic origin. In this internode 

 there are transitional bundles of several types, as well as scattered 

 groups of xylem and phloem elements in various orientations. 

 The transition is practically complete at the third node, and the 

 internodes above this point have a meristele of collateral bundles. 



Early in ontogeny, the final pattern of the plant is determined. 

 By the time the stem axis is an inch long or even less, all the plant 

 structures — leaves, nodes and internodes, terminal tassel, lateral 



