IO2 



THE WHEAT PLANT 



The form of the apex of the empty glume differs considerably in the 

 various kinds of wheat ; in some it is broad with a blunt extension of 

 the midrib, in others it is narrower with the central nerve continued into 

 an acute point ; in certain forms of T. vulgare and T. compactum from 

 Central Asia it possesses a terminal scabrid awn from 2 to 5 cm. long, but 

 in the majority of wheats the terminal tooth or keel is not more than a 

 few millimetres in length. 



In T. aegilopoides and T. monococcum the empty glume has a lateral 

 secondary tooth on its broad outside half, in addition to the primary 

 central one ; in most other wheats the secondary tooth is short or 

 altogether absent. 



The empty glumes of the terminal differ from those of the lateral 

 spikelets ; they are rarely keeled and always symmetrical, a line down 

 the centre dividing them into two similar halves. In some wheats these 



glumes have single, well-defined 

 midribs ; in others the midrib 

 is missing, in which case two 

 strong lateral veins are present, 

 one on each side of the central 

 line, the apex being notched or 

 divided sometimes to near the 

 base of the glume (Fig. 78). 



The colour of the glumes is 

 white, red, or black, but of each 

 of these tints there are many 

 shades. Whatever the natural 

 hereditary tint, its full develop- 

 ment is dependent largely upon the intensity of the light, heat, and atmo- 

 spheric moisture during ripening. In certain varieties of T. dicoccum, T. 

 durum, and T. turgidum the tint is a creamy white, but in the majority of 

 the white-chaffed varieties it is pale yellowish ; in a few Persian forms 

 the glumes are a clear canary-yellow colour, and occasionally pale emerald 

 green. 



Among red-chaffed wheats the range is very wide, extending from the 

 palest shades of red through deeper tints of brick-red to dark chestnut 

 and sooty brown. 



Black-chaffed varieties are comparatively rare, although examples are 

 met with in all the races of wheats. Several shades are included under 

 the term " black." In some glabrous forms the chaff is almost jet black, 

 in others a dark sooty brown ; these colours when overlaid by a pale 

 waxy covering or a felt of soft hairs are modified to bluish black or 

 mouse-grey tints. 



In most black-chaffed wheats the colour is only developed to its 



FIG. 78. Empty glumes (T. turgidum) ( x 3). 

 a and c, from terminal spikelet ; b, from a 

 lateral spikelet. 



