TRITICUM 



151 



spaces. Their long axes are parallel to those of the cells of the 

 epicarp; and, because of their loose arrangement, they appear as 

 rings in transection. (Fig. 63.) 



The seed coat is much crushed at maturity, and appears as a zone 

 of cells in which the walls can scarcely be distinguished. Its 

 ontogeny is described in connection with the development of the 

 ovule and embryogeny. The nucellar tissue or perisperm is, for 

 the most part, resorbed in the development of the grain, and may 

 be completely absent at maturity. When present, it consists of one 



op£2=' 





-ecp 



-hd 

 -i c 



pep 



—end 



Fig. 63. Transection of a portion of a mature grain showing detail of pericarp, integuments, 

 nucellus and endosperm : «/, aleurone layer ; c>- c, cross cells ; ^cp, epicarp; ?«</, endosperm ; 

 hd, hypodermis; / c, intermediate cells; nls, nucellus; pep, pericarp; s c, seed coat; st, 

 starchy endosperm; t c, tube cells. (Redrawn from Tschirch and Oesterle, Anatomischer 

 Atlas der Pharmakognosie und Nahrungsmittelkunde, Herm. Tauchnitz.) 



or two layers of cells with thickened walls which overlie the 

 aleurone cells; and, in the mature grain, they are commonly 

 crushed so as to form a bright colorless line, the hyaline layer. 

 The aleurone cells constitute the outer zone of the endosperm, 

 which is usually a single layer except in the region of the furrow; 

 and the thick-walled cells appear square or rectangular in a transec- 

 tion of the grain, being more or less rounded to polygonal in 

 surface view. They contain an abundance of protein granules and 

 some fat. The protein appears to be formed by condensation 

 processes during the desiccation of the wheat kernel. 



