GERMINATION OF THE GRAIN 29 



grains granules of protein, each possessing one or more excessively 

 minute globoids are present in the parenchyma of the scutellum and other 

 parts of the embryo. 



Before germination begins, the columnar epithelium of the scutellum 

 is devoid of starch, but its cells contain dense cytoplasm and an oval 

 nucleus, which usually rests in the lower half of the cell with its long axis 

 arranged lengthwise in the cell lumen. 



In 12 to 1 6 hours after germination commences in grains sprouting 

 indoors at i8-2o C. starch granules make their appearance in the cells 

 of the coleorhiza, root-cap, and tip of the coleoptile ; these are derived 

 chiefly from fat globules or from a soluble carbohydrate stored in the 

 tissues of the embryo and not from the endosperm, since they arise in 

 portions of the embryo which have been cut from dry grains and laid upon 

 damp filter paper. Nevertheless, dissolved reserves soon begin to be 

 transferred from the endosperm to the growing embryo, and in 24 to 36 

 hours fine-grained starch is found in the epithelium of the scutellum, 

 and in greater abundance in the parenchyma of the latter. Increas- 

 ing quantities are seen also about this period in the fully developed 

 cells of the root-cap, in the coleoptile, especially near its apex, and in the 

 coleorhiza ; a small amount is present in the endodermis of the primary 

 root. 



The grains are usually spherical, about i //, in diameter, and many 

 of them compound, consisting of two or three partial granules. Their 

 special accumulation in the root-cap and apical cells of the coleoptile 

 supports the view of Haberlandt and Nemec that they act as statoliths 

 in the geotropic curvatures of these parts. 



The reserves stored in the endosperm are rendered soluble by various 

 enzymes. Among the latter, whose presence has been established in 

 germinating cereal grains, are cytase and the amyloclastic enzyme diastase ; 

 presumably, proteoclastic ferments capable of breaking down the reserve 

 proteins also occur in the grain, but these have not been investigated 

 in wheat. 



The dissolved plastic materials are absorbed by the columnar 

 epithelium, and passed on through the parenchyma and the vascular 

 system of the scutellum to the growing regions of the young plant. 



In the resting state of the embryo the cylindrical epithelial cells are 

 from 30 to 40 p long with somewhat rectangular ends and dense proto- 

 plasmic contents. As germination advances, the cells elongate until they 

 are 80-90 /u, long, when absorption is most active, their tips, at the same 

 time, becoming swollen, club-shaped, and separate from each other, 

 projecting into the endosperm (Fig. 19). The vascular strands per- 

 meating the scutellum become more highly differentiated, and many of 

 the walls of the scutellar parenchyma thickened and pitted. 



