THE GRAIN 17 



Sachs, and others look upon it as an outgrowth of the hypocotyl or 

 radicle. 



The epiblast, according to Bruns and Celakowsky, is a reduced second 

 cotyledon ; others suggest that it is a scale-like trichome ; to Worsdell 

 it is a part of the cotyledon, and corresponds to the auricles at the base of 

 the blade of a green foliage leaf. 



The coleoptile or plumule-sheath is regarded by Hofmeister and 

 Sachs as the true cotyledon, while Van Tieghem, Klebs, and Worsdell 

 describe it as the ligule of the chief cotyledon, the blade of which is the 

 scutellum ; to Bruns and others it represents a bladeless leaf, the first 

 of the plumule, the second being the first green foliage leaf of the plant. 

 The view which I think is most in agreement with the development and 

 structure of the embryo of wheat (see pp. 133-136) is that which regards 

 the scutellum, epiblast, coleoptile, and first green leaf as the first four 

 leaves of the plant. The alternate distichous disposition of these structures 

 on opposite orthostiches also supports this conclusion. 



A comparison of the arrangement and relationship of the adventitious 

 roots to the buds and leaves at the " tillering " nodes of the older plant 

 suggests that the three pairs of opposite seminal rootlets of the young 

 wheat plant are associated with three leaves scutellum, epiblast, and 

 coleoptile the plane through them being at right angles to the median 

 plane of these reduced leaves, an arrangement similar to that of later 

 roots which spring from the older parts of the axis bearing the foliage 

 leaves (see pp. 36-38). 



The rootlet which appears at right angles to the plane of the rest, 

 above the epiblast, suggests the suppression of a bud in the axil of the 

 latter, a corresponding opposite rootlet frequently developing from the 

 base of the axillary bud of the coleoptile. 



Colour of the Grain. One or two Abyssinian varieties of T. dicoccum 

 possess grains which are a rich purple tint when freshly ripened, the 

 colour being due to the presence of an anthocyan pigment located chiefly 

 in the chlorophyll or " cross " layer of the pericarp (p. 8). 



All other wheats have grains which are usually classified as " white " 1^ 

 or " red." The distinction is based on the character of the testa : in 

 " white " wheats the latter is colourless, while in " red " wheats an oily 

 or resinous material develops in the cell lumen and cell walls of its two 

 cell layers during ripening. 



The particular shade exhibited by the grain is, however, dependent 

 not only upon the amount of colour in the testa, but upon the thickness, 

 tint, and transparency of the superposed pericarp, and the " mealy " 

 and " flinty " character of the endosperm. 



The pericarp is translucent, and in grains ripened in a hot, dry season 

 is a pale creamy tint, like that of clean unweathered straw. 



c 



