12 



THE WHEAT PLANT 



parenchyma are crushed together, forming a narrow band 35-40 fju broad, 

 devoid of starch (r, Figs. 10 and u). The majority of the cells, however, 

 are filled with starch grains imbedded in a protoplasmic matrix, from 



which gluten is derived on treatment 

 with water ; more or less disin- 

 tegrated nuclei may be recognised, 

 but no aleuron grains are present. 

 The starch grains in the cells 

 immediately within the aleuron 

 layer are small 8 to 10 p in 

 diameter and more uniform in 

 size than those found in the larger 

 inner cells of the endosperm. In the 

 latter two forms are seen, namely, 

 large lenticular grains of circular or 



FIG. 9. Front view of the embryo. 

 s, Scutellum ; p, plumule ; /, epiblast. 



elliptical outline measuring from 28 to 40 ^ 

 across, and much smaller grains almost 

 spherical, rarely more than 6 or 8 \i in dia- 

 meter. In each of the larger grains is a small 

 central hilum surrounded by faint rings. 



(d) The Embryo. The embryo of the 

 wheat plant lies on the dorsal side at the 

 base of the grain, one side of it in close 

 contact with the endosperm, the other being 

 covered only by the seed-coat and pericarp. 



It is a highly differentiated body, pos- 

 sessing a short hypocotyl, at the apex of 

 which is the plumule or primary bud, com- 

 posed of rudimentary leaves surrounded 

 by the coleoptile or plumule-sheath, and at 

 its base, the root -system, completely en- 

 closed by the coleorhiza or root-sheath 

 (Figs. 9 and 10). 



Attached to one side of the axis, and 

 forming the greater portion of the embryo 

 as it exists in the grain, is a fleshy shield-like 

 structure named by Gartner the scutellum ; 

 on the other side, opposite to the scutellum, 

 is a small, tongue -like organ termed the 

 epiblast by Richard (e, Fig. 10). 



r 



u 



FIG. 10. Longitudinal section of 

 the embryo ( x 25). p, Pericarp of 

 the grain ; o, aleuron layer ; r, 

 crushed empty cells of the endo- 

 sperm ; s, scutellum ; a, epithe- 

 lium of scutellum; v, "ventral" 

 scale of scutellum ; o', coleoptile ; 

 /, ist grain foliage leaf; e, epi- 

 blast ; h, primary root ; n, coleo- 

 rhiza ; d, bud in axil of coleoptile. 



