MORPHOLOGY OK THE BARLEY GRAIN. 
15 
of a ripe barley grain treated with Millon's solut ion presents a strongly 
polored hand just inside the alenrone layer and completely sur- 
rounding the rest of the endosperm, showing the relatively high 
proteid and low carbohydrate content of this region. The cell 
contents, therefore, are obviously not identical with those beneath. 
It is but reasonable to suppose that these young and loosely tilled 
cells would be more easily broken down and that diastase, acting 
from the proximal end of the grain, even if distributed equally over 
the surface of the endosperm, would advance most rapidly along this 
area of least resistance. A strong point against the aleurone theory 
of digestion is the fact that the cells of the endosperm first affected 
are those next to the scutellum, as shown in Plate IV. If the aleurone 
layer is active, why should not this take place uniformly in those 
ceils lying directly beneath that layer? Sections made through 
grains germinated at high temperatures show the proximal end of 
the endosperm to be in complete solution, while the cells next to the 
aleurone layer toward the distal end of the grain are entirely un- 
affected. This can not be due to a lack of water, for water can be 
shown to pass readily through the walls of all parts of the grain. 
One or two authors have attempted to ascribe this condition to a 
certain inexplicable stimulus which proceeds from the growing 
plantlet and passes through the connected plasma of the aleurone 
cells, inciting them to successive action. Such theory fails to explain 
why the movement advances much more rapidly along the furrow 
than elsewhere. The cells in this region are for the most part dead 
tissue and would be incapable of aiding the aleurone layer or of car- 
rying any stimulus. However, since the region of the furrow con- 
tains the conducting tissue during the development of the grain and 
since it leads past the scutellum, it is readily seen that it could be still 
instrumental in earning secretions from that source, although inca- 
pable of conveying stimuli. 
A more plausible defense of the theory of aleurone secretion has 
been advanced in the statement that the enzyms are able to work only 
when the products of their conversion are removed, and that the 
scutellum as an absorbing organ is responsible for the fact that the 
action commences adjacent to it and can not proceed elsewhere, 
except as the process of removal becomes effective. This theory is 
not borne out by observations, in that the lack of a means of removal 
would not prevent the preliminary stages of dissolution from taking- 
place at all points in contact with the aleurone layer. No such effect 
occurs. Moreover, the percentage of maltose necessary to the in- 
hibition of diastatic action is very high, certainly not less than 30 
per cent. That this percentage is seldom reached is shown by the 
fact that the cells first acted upon while in a partial state of conver- 
sion pass on to the point of complete dissolution, even though they 
