14 BULLETIN 183. U. S. DEPARTMENT OF AGRICULTURE. 
Tangl 1 has shown that the thickened cell walls in the endosperm 
of many seeds are provided with openings, so that the cell contents 
are not isolated but in intimate contact. This is true of the aleurone 
layer of barley, and the layer is in consequence more nearly a unit 
than might be supposed. 
The accumulative importance of these and other facts has caused 
many authors to assert that the aleurone cells have a very important 
secretive function. The views of the individual experimenters who 
are inclined to this opinion are too numerous to discuss separately. 
The points of variance between them and the writers are few and 
turn largely on the 
interpretation of 
specific phenomena. 
These differences 
really center around 
a single fact. When 
the breaking down 
of the starch endo- 
sperm once com- 
mences next to the 
scutellum, it follows 
rapidly through the 
cells immediately 
beneath the aleurone 
layer. This point is 
frankly admitted, 
but is far from being 
a proof of aleurone 
activity. It has other 
interpretations more 
consistent with the general facts of germination. These cells adja- 
cent to the aleurone layer are markedly different from those of the 
rest of the endosperm. They are younger. The starch endosperm 
is laid down and its cells filled in centrifugal order, so that its 
outer areas are the latest in formation and the latest in starch infil- 
tration. They are also less gorged with starch. A grain of barley 
is not definitely limited in growth. In a way its growth is inde- 
terminate, its development progressive until stopped by the act of 
ripening, a stage in which the failure of the supply of food is a marked 
factor. As may be seen in Plate III, the outer cells must from their 
very nature be younger and less filled with starch, their walls less 
desiccated, and their nuclei in a more nearly normal condition than 
those of the more thoroughly matured storage cells. A cross section 
sS 
Fig. 3. — Section of piece of "brewers' grain," that is, of a barley grain 
that has passed through both the malting and the mashing processes. 
The aleurone layer remains unchanged. The cell contents are 
slightly shrunken by heating in the mash tub. The starch endo- 
sperm is fully depleted of its contents. 
i Tangl, Eduard. Ueber offene Communicationen z-.vischen den Zellen des Endosperms einiger Samen. 
Jahrbucher fiir Wissenschaftliche Botanik [Pringsheim], Bd. 12, Heft 2, p. 170-189, pi. 4-6 [1880]. 
