Embryo and Aleurone Layer of Hordeum. 1169 
The above results show on the one hand that the secretory capacity of 
the scutellum falls as germination proceeds, on the other, that the amount 
of amylase found in the scutellum during the period 0-4 days 1 is con¬ 
siderable, and if we assume, as we may reasonably do, that a very large 
proportion of this is destined for external use in the inner endosperm, then 
the amount of enzyme found in the culture media of embryos on artificial 
culture is far from over-estimated. The period 0-7 days appears to 
represent the limits of great secretory activity; from the eighth day onward 
the level of amylase production falls considerably, and the functions of the 
scutellum are in all probability during this period principally absorptive. 
Beyond the period 0-4 days the cytological changes are more difficult 
to follow, although distinct nuclear changes are very evident, showing, as do 
the data in the foregoing table, that the cells are actively functioning. 
In short, the evidence here adduced relative to the amyloclastic 
capacity of the scutellum indicates that the capacity of the embryo is much 
superior when attached to its natural endosperm than when cultivated even 
on the most suitable of the artificial media so far essayed. A similar 
conclusion with regard to the capacity of the aleurone layer may be 
suggested by a comparison of its amylase content under similarly defined 
conditions of comparison (Section XIV). 
X. The Secretion of Cytase by the Embryo and Aleurone 
Layer. 
The existence of a cellulose-dissolving ferment in germinating barley 
was noted by Brown and Morris (loc. cit.), and they state that the 
disintegration and dissolution of the cell walls of the amyliferous cells which 
commence at the onset of and continue during the progress of germination 
are due to a specific enzyme, cytase. 
The seat of the production of the enzyme, they state, is the columnar 
(absorptive) epithelium of the embryo; the later work of Brown and 
Escombe (loc. cit.) shows that the principal seat of elaboration of this 
cytoclastic enzyme during germination is probably the aleurone layer. 
1 Cytological study of microtomed stained sections of the scutellum during the period 0-4 days 
affords evidence which in certain essentials is in no way opposed to the biochemical data given above. 
During the period 0-4 days, the solubilization of the conspicuous ‘ aleurone ’ and other grains with 
which the cytoplasm is crowded initially proceeds most actively; commencing in the sub-epithelial 
tissue it progresses gradually to the deeper-lying portions of the scutellar tissue. Within the period 
mentioned the great mass of these grains are rendered soluble and disappear from view. There is 
undoubtedly some correlation between this disappearance of storage substance and the production of 
amylase. The period does not represent one of remarkable growth. These substances do not serve 
purely for purposes of general nutrition, but in all probability largely for the more important work 
with which the scutellum is occupied at this phase, viz. enzyme elaboration, which proceeds in the 
specialized epithelial layer. 
