314 



PHYSIOLOGY OF NUTRITION. 



sulphate and potash. The main mass of the endosperm is seen to 

 consist of cells rounded in cross section, Avhich contain starch 

 grains of different sizes, and proteids. The latter are to be de- 

 tected by treating sections with Copper sulphate and potash solu- 

 tion. The embryo lies at the side of the endosperm. To study 

 the embryo, median longitudinal sections of the wheat grain are to 

 be prepared. These, as seen first under a low power of the micro- 

 scope, then under a high power, present a complicated appearance 

 (see Fig. 71). Attention must first be directed to the part of the 

 embryo abutting directly on the endosperm. This is the shield 

 (scutellum) which demands our special at- 

 tention. It mainly consists of small 

 rounded cells ; but the layer of cells 

 bordering upon the endosperm is different 

 in character, as can more especially be 

 seen by treating the sections with potash 

 solution. The cells, viz., of this epithelium 

 of the scutellum are elongated and cylin- 

 drical in form. At the upper part of the 

 embryo we further recognise the closed 

 sheath leaf, the young rudiments of foliage 

 leaves, and the vegetative cone. The root 

 of the wheat embryo is surrounded by a 

 root sheath (coleorhiza), the boundary be- 

 tween the two being marked by a bright 

 line. Starch or glucose are present 

 neither in the cells of the scutellum, nor 

 in those of the rest of the embryo. On the 

 other hand, all the cells of the embryo 

 contain large quantities of proteid. It is 

 of further to be noted that the endosperm 

 of the resting wheat grain also contains no 

 sugar. 



If soaked wheat grains are placed on plates of pumice-stone 

 lying in water, germination at once begins, the organs of the em- 

 bryo growing at the expense of the plastic materials [conveyed to 

 them & from the endosperm. .The root emerges, and the first lateral 

 roots, which develop henceforth more rapidly than the primary 

 root, make their appearance. Similarly the primordia of the leaves 

 rapidly undergo considerable elongation, bat they still remain at 

 first enclosed by the actively growing first sheath leaf (see Fig. 



FIG. 113. Seedling 

 Triticum vulgare. 



