154 THE STRUCTURE OF ECONOMIC PLANTS 



colp 



node and may extend up the first internode a short distance 

 before becoming a part of the stele. (Fig. 65.) 



According to Avery (i), the median third of the scutellar bundle 

 becomes a part of the stele directly; and extends downward as a 

 part of it to the scutellar node, where it turns upward. At the 

 point of upward curvature, vascular strands from the root anasto- 

 mose with it, and the combined strand becomes the midrib of the 

 foliage leaf above the coleoptile. (Fig. 66.) Each of the outer 



branches proceeds laterally 

 upward and again forks to 

 form two bundles, the outer 

 one of each pair being a cole- 

 optilar trace. In T. vulgare, 

 two unbranched bundles pass 

 from the base to the apex of 

 the coleoptile; but in some 

 level of scu no species of Triticum, as many 

 as six have been reported by 

 Percival (11). The inner 

 bundle of each pair, after 

 passing upward in the axis, 

 branches and gives rise to 

 one or more bundles which 

 constitute the trace of the 

 first foliage leaf above the 

 coleoptile. 



Interpretation of the 



lat sem rts 



— -/ — coir 



~ pri rt 



Fig. 65. Diagrammatic face view of the embry- 

 onic axis showing the procambial vascular system 

 in black : colp, coleoptile; coir, coleorhiza ; lat sem 

 r.., lateral seminal roots, /,..>/, primary root ; scu £^^^^0 AND THE SeEDLING 

 no, scutellar node. QAiter Avery. j 



Axis. — The structure of the 

 embryo and the seedling axis of the grasses has occupied the atten- 

 tion of morphologists for over a century; and there has been no 

 general agreement in the interpretation of the various parts of the 

 embryo. This has resulted in a voluminous literature which is 

 well summarized by Avery (i), McCall (9). 



Percival (10) states that the view which "is most in agreement 

 with the development and structure of the embryo of wheat is 

 that which regards the scutellum, epiblast, coleoptile, and first 

 green leaf as the first four leaves of the plant." McCall (9) 

 interprets the epiblast "as a vestigial leaf," the scutellum as 

 "the functional cotyledon, divergent from the second node" and 



