A GRAIN OF BARLEY. gt 
or bristle @, which is closely attached to the inner palea, and 
lies in the furrow of the grain. The various integuments are 
better seen in Fig. 3, which represents a transverse section 
of the grain taken across the middle. The inner part of the 
section is taken up with the starch-containing cells of the 
endosperm, which are surrounded by a triple layer of thick- 
walled, rectangular cells, @/, not shown in detail in this Figure. 
These are the so-called aleurone cells; they contain a very 
finely granulated substance which is very different in composi- 
tion from starch, and they form the outer layer of the 
endosperm, that great reservoir of material whose function it 
is to supply food to the growing embryo. 
Surrounding this aleurone layer we find the true covering 
of the seed, the testa, 4 and outside this, and closely adherent 
to it, is another thin coating, f, corresponding to the covering 
of the fruit in other plants, and hence called the fericarp. 
The pericarp and testa can each in their turn be differentiated 
into various layers, but for my present purpose it is not 
necessary that I should more minutely describe them. I wish 
you to notice very particularly in this section, that both the 
testa and pericarp have a common point of origin, ff., which 
in the transverse section of a barley-grain is marked by a 
very distinct reddish yellow spot. This is the cross section 
of a well-marked line of tissue, which runs along the entire 
length of the grain, and is the so-called ‘ pigment-string,” 
the true nature of which will be rendered clear later on. 
Outside the pericarp we have the thick outer skin, formed 
by the two over-lapping palez, 7.2. and /.s. 
In Plate II. you have all these structures shown in a more 
highly magnified form, the drawing representing very accurately the 
various tissues of the lower part of a grain of barley as seen 
in a longitudinal ‘section under a fairly high power. I shall 
revert to this Plate presently, but before we can fully under- 
stand it in all its details it is necessary to examine with great 
minuteness the development of the flower of the barley plant 
from its period of blossoming to the ripening of the grain. 
