A GRAIN OF BARLEY, ¥ 10] 
transverse section they are seen to have a general radial 
arrangement. See Plate I., Fig. 3. 
By the direct observation of very thin sections under the 
microscope we can detect nothing in them except tightly- 
packed starch granules, but if these are carefully dissolved out 
by suitable re-agents, we find, on staining the preparation with 
iodine, that the little grains of starch are embedded in a very 
fine network of proteid material, which is the remnant of the 
protoplasm, that wonderful formative material out of which 
both -cell-walls and cell-contents have been produced. In the 
case of the wheat-grain this remnant of cell protoplasm is left 
behind, on kneading and crushing the flour, in the form of a 
sticky tenacious mass, known as g/uten. It has a very com- 
plex composition, and may be separated into several distinct 
substances, having somewhat different properties, but all 
belonging to the a/buminous class of bodies, of which the 
white of egg may be taken as a type. One great characteristic 
of all these albuminous bodies is that they contain a large 
percentage (13 to 15) of nitrogen. 
The three rows of cells in the outermost or peripheral 
portions of the endosperm, which, as I have just shown you, 
_are represented by only one row in the case of wheat, are 
very different in appearance from the inner starch-containing 
cells. Unlike the latter, they are, when seen in transverse 
and longitudinal sections, nearly rectangular in form, and 
have very thick cell walls, which swell up somewhat under 
the action of water. They do not contain a trace of starch, 
but are filled with closely packed, very minute, yellowish 
‘granules, the so-called aleurone grains. It is only of late 
that we have begun to understand that these do not consist 
‘of one homogeneous substance as do the starch-granules ; but 
that the aleurone-cells contain a mixture of several distinct 
‘substances in the granular form. To convince oneself of this, 
it is necessary to take tangential sections of a grain deprived of 
its outer husk, and to treat them with various chemical re-agents. 
Plate V., Fig. 12, is a photo-micrograph of such a tangen- 
tial section through the aleurone layer of barley. 
