THE BARLEY-CORN. 
227 
that the embryo pushed its plumule through the pericarp upon 
germination, but instead of growing in a direction determined by 
its responses to light and gravitation, it is held against the peri¬ 
carp by the palea, which, however, is not seen in this figure. 
Immediately below the pericarp,* which appear merely as a 
dark line, lies a layer of cells with thick walls. This is the 
aleurone layer. The cells contain oil and some proteids, and 
there is evidence that they are important, physiologically, in that 
they secrete digestive principles which act upon the endosperm. 
It is not at all evident to a beginner in botany that the embryo 
lies within the endosperm. Indeed this point is scarcely ever 
thought of, although it is evident enough in many other forms, 
Fig. 43. A portion of the endosperm and the adjacent pericarp (Per.) 
under high magnification. AL, aleurone layer. 
as, e.g., castor oil. While the position of the embryo is very much 
on one side, that it lies embedded in the endosperm is clear from 
Fig. 42, in which may be seen the aleurone layer (al) (the outer 
zone of endosperm cells) passing around the scutellum of the 
* According to a number of students the layer of cells which I have 
called the pericarp includes, on its inner face, the seed-coat or testa, recog¬ 
nizable by its brown color (Pammell). I have not been able to satisfy 
myself of the correctness of this view, and I have therefore, upon com¬ 
parative grounds, taken the present position. 
