io6 



THE WHEAT PLANT 



The structure resembles that of the internodes of the culm. On the 

 outside is an epidermis of oblong cells, their length from 6 to 10 times their 

 breadth, with sinuous thickened walls and oval or kidney-shaped " dwarf " 

 cells alternating with them. At the edges are unicellular epidermal hairs 

 of variable length. 



Lines of stomata resembling those of the stem occur in the epidermis 

 overlaying the longitudinal bands of chlorophyllous parenchyma which 

 are found just beneath the epidermis on the convex side only. These 



FIG. 80. Transverse sections of the rachis ( x 25). A, a lower internode ; B, an upper 

 internode ; s, stereome ; c, chlorophyllous tissue ; r and x, vascular bundles. 



green bands are most abundant in the lower internodes of the rachis (c, 

 Fig. 80), being reduced to two or three narrow lines near the edges in the 

 upper portions. Within the epidermis on the flatter side of each inter- 

 node of the rachis which is hidden by the back of each spikelet there is a 

 continuous band of stereome (s, Fig. 80). 



The central part of the rachis is more or less completely filled with 

 thin-walled ground parenchyma, imbedded in which are numerous 

 vascular strands, the larger ones arranged in a circle or ellipse, the smaller 

 bundles being found close to the inner side of the chlorophyllous bands. 



