io8 



THE WHEAT PLANT 



In transverse section it is seen that near the margins of the glume 

 the space between the outer and inner epidermis is occupied by strong 

 thick-walled ground tissue traversed by vascular bundles and narrow 

 longitudinal bands of assimilating tissue which lie 

 close to the outer surface. 



Away from the margins the glume is thinner and 

 the stereome extends only to the middle of the 

 section, the inner half consisting of thin- walled 

 chlorophyllous parenchyma covered by an epidermis 

 of larger thinner-walled cells than those on the 

 outside of the glume. 



A number of vascular bundles run from the base 

 to the tip in bearded glumes ; the central one and 

 two of the lateral strands are continued into the awn. 

 The awn tapers from the base to the tip, and is 

 triangular in section, the sides approximately equal. 



One of the sides is parallel to the flattened rachilla 

 and is continuous with the inner surface of the 

 glume -to which the awn belongs, the two other sides 

 corresponding to the outer surfaces of the right and 

 left halves of the glume. 

 FIG. 82. Portion of an The epidermis is composed (i) of narrow elon- 



awn of T. turgidum j n i n i i 1 



( x 35). c, Band of gated cells with walls showing wavy thickening and 

 chlorophyllous tissue ; numerous simple pits, (2) small oval or squarish 



n, scabrid hairs. r ., , . 



dwarf cells often projecting as papillae, and (3) 



short thick- walled unicellular hairs with fine points which are directed 

 forwards and give the awn its scabrid character (h, Fig. 82). In the 



FIG. 83. Transverse sections of an awn of T. turgidum (*so). A, Near the base ; B, 

 at the middle ; C, near the apex ; s, stereome ; c, chlorophyllous tissue ; x, stoma ; 

 b, vascular bundles. 



epidermis on the two outer faces of the awn are longitudinal lines of 

 stomata which communicate with green assimilating tissue within. The 

 latter consists of two separate bands of chlorophyllous parenchyma, 



