1 32 THE WHEAT PLANT 



(iii.) Antipodal Cells. As the growth of the embryo and endosperm 

 proceeds the antipodal cells slowly degenerate, the cytoplasm disappearing 

 first, debris of the large nuclei being visible for some time after the cells 

 have been stretched and flattened by the growth of the surrounding parts 

 of the ovule. 



(iv.) Filling of the Endosperm Tissue. The storage of the endosperm with 

 reserves begins when the tissue is completely formed, i.e. 10-14 days 

 after fertilisation, and continues for five or six weeks, till the grain is ripe. 



The course of events in regard to the deposition of starch is readily 

 followed. The soluble carbohydrate from which it is formed is manu- 

 factured in the stems and leaves of the plant and sent along the conducting 

 strand which enters the base of the ovary, and traverses the raphe on the 

 furrow side of the anatropous ovule to the morphological base of the 

 latter in the upper part of the ovary ; from this point it diffuses into the 

 endosperm, and it is in this region away from the embryo that starch 

 grains are first observed in the centre of the two " cheeks," right and left 

 of the furrow of the ovary. 



When the endosperm tissue has almost or quite completely filled the 

 cavity of the embryo-sac, minute starch grains are first seen near the nuclei 

 of the cells ; later, they are produced at many points in the cytoplasm 

 and increase rapidly in number and size, growing into thin lenticular 

 structures which for a time are all similar in diameter. 



Not all the reserve cells are filled with starch at the same time nor at 

 the same rate. About three weeks after fertilisation those in the upper 

 part of the ovule are crowded with fully-formed grains ; half-way down 

 and along the furrow to near the base they are only partially filled with 

 smaller grains, while the cells in closer proximity to the embryo contain 

 but a few minute grains or none at all. In five or six weeks all the cells 

 of the endosperm contain starch, except those of the aleuron layer, and a 

 few layers in contact with the back of the scutellum ; ultimately, the 

 majority become densely packed throughout with starch grains of various 

 sizes, those formed in the later period of ripening remaining small. 



The greatest amount and the largest grains are formed in the large 

 cells in the centre of the " cheeks " of the grain, the peripheral region 

 of the endosperm containing a small proportion of starch and a large 

 number of small grains. 



The deposition of starch progresses from the upper part of the grain 

 towards the embryo in a diagonal plane, roughly parallel to the back of 

 the scutellum. 



The part of the grain stored last lies round the upper margin of the 

 scutellum on the dorsal side, a region which is frequently opaque and 

 mealy in ripe grains, in which the rest of the endosperm is translucent 

 and flinty. 



