1 26 Brenchley. — On the Strength and Development of 
opposite the furrow, are marked off from the rest by their smaller size and 
denser protoplasmic contents. Eventually a peripheral layer of such 
smaller cells is marked off, appearing on the dorsal side about a fortnight 
after pollination. This external layer develops into the aleurone layer, 
which is highly specialized in the cereals, and consists of small regularly- 
arranged cells with dense protoplasmic contents and well-marked nuclei, 
which persist unaltered right up to maturity. No starch grains are present, 
but instead there is a great accumulation of protein matters which are 
probably of different chemical composition from those in the rest of the 
endosperm. The cells in the bulk of the tissue, on the other hand, are 
large, varying much in size and shape. The protoplasmic contents are 
reduced to a minimum in the ripe grain, being drawn out into a very 
attenuated reticulum, and the nuclei undergo definite disorganization, as 
will be seen later. The protein matters are chiefly to be seen in the cells 
lying just below the aleurone layer, but the most marked feature of the 
cell contents is the enormous amount of starch deposited as grains of 
different sizes. 
Certain microscopical tests were carried out to ascertain the behaviour 
of the aleurone layer during the manufacture of flour, two separate sets of 
wheat flour, specially milled by Mr. A. E. Humphries, from Coxes Lock 
Mills, Weybridge, being used for the purpose. 
In the modern process of roller milling, the wheat grains are gradually 
reduced by being passed through successive pairs of revolving rollers (14), 
so that eventually the whole of the central part of the grain is cleared away 
from the coverings, which form the bran. After each crushing or rolling 
the finest particles are sifted out and form the various grades of flour, and 
samples of these, including the bran, were sent to me for investigation. The 
flours were subjected to close microscopic scrutiny, with and without staining 
in various ways, in order to find out whether the aleurone cells were ever 
present in the flour itself. Very seldom indeed could any of these cells, 
even isolated ones, be observed in the flour of any grade — all the samples 
could be considered as practically pure in this respect. The reason was 
obvious when an examination of the bran was undertaken. In the initial 
processes of cracking or 4 breaking * the grain, the aleurone layer had split 
simultaneously with the fruit-coats, and remained firmly adherent to them ; 
in the subsequent milling the whole of the starchy endosperm tissue was 
torn away, and ultimately converted into flour of different grades, while the 
aleurone layer remained behind in small sheets, so to speak, and formed 
part of the bran. This is probably due to the fact that the junction between 
the thin-walled cells of the starchy endosperm and the very resistant and 
thick-walled aleurone cells offers the line of least resistance to the pressure 
applied during the process of milling. 
2 . Infiltration of Starch . The deposition of starch in the endosperm 
