THE GRAIN 



(i.) The scutellum resembles a broad elliptical shield, measuring 

 3 mm. by 2-5 mm. and about -3 mm. in thickness, with a thinner rim. 

 It is slightly curved, the convex surface fitting closely to the endosperm. 

 The upper free portion extends about 1-3 mm. beyond the point of 

 attachment to the axis, and partly surrounds the coleoptile, the latter 

 being sunk in a slight depression in the scutellum. The portion which 

 projects over the apex of the coleoptile is sometimes termed the coty- 

 ledonary sheath or ventral scale (v, Figs. 10, 107). 



The epidermis of the back of the scutellum in contact with the endo- 

 sperm consists of elongated cylindrical cells 35-40^ long and 8-10 p 

 broad, the long axes of which are arranged at right angles to the curved 



FIG. ii. Transverse section of a 

 portion of the back of the scutellum 

 and adjacent endosperm (x2io). 

 , Epithelium of the scutellum ; r, 



crushed empty cells of the endo- FIG. 12. Gland-like cavity from the scutellum of 

 sperm. T. dicoccum ( x 200). 



surfaces of the scutellum (a, Figs. 10 and n). It is termed the columnar 

 epithelium or epithelial layer ; and in the embryos of T. dicoccum, T. 

 durum, and some other wheats, portions of it are deeply inverted into 

 the form of simple tubular glands, especially near the upper and lower 

 edges of the scutellum (Fig. 12). Its cells secrete diastase, the enzyme 

 which renders soluble the reserve starch stored in the endosperm tissue, 

 and it functions also as a haustorium through which all the dissolved 

 plastic materials of the endosperm are absorbed and transferred to the 

 embryo when germination occurs. 



(ii.) The epiblast or lobule is a short, thin scale (e, Fig. 10) about 170 p 

 long, 550 p broad at the base, and about 82 /x thick ; it is attached to the 

 axis slightly above the point of insertion of the scutellum, and consists of 

 parenchyma only, with no vascular system. 



