The Development of Endosperm in Cereals. 



113 



iDetween the dividing cambial layer and the general endosperm is 

 not so well marked, but the details of cell-division are clear 

 in the outer layer, which appears several cells deep owing to 

 the obliqueness of the section. 



Surrounding the endosperm there is a single layer of large 

 cells, the contents of which have practically disappeared; this 

 is the remains of the nucellus (5), which has been displaced and 

 absorbed by the developing endosperm. It appears as a layer of 

 disorganising cells in the young grain, but has disappeared when 

 the grain is ripe. Beyond this there is a layer of silica, which 



Text Figure VIII. 



Transverse section of ripe oat grain. 



A — Single aleurone layer. 

 B — Endosperm. 



-was probably deposited in the outer wall of the embryo-sac — 

 this forms the so-called testa which is not really a seed-coat, 

 ;since it is devoid of any cellular structure. 



The ovary wall contained starch which was absorbed by the 

 •embryo during its development (Text Fig. VI). As the starch 

 is used the cells become empty, and the nuclei can be seen in 

 process of degeneration. Later the cell-walls thicken and 

 •develop into the pericarp of the ripe grain. The final stages, 

 where the resting cambium appears as the aleurone layer, are 

 .•shown in a transverse section of an oat grain (Text Fig. VIII.), 



