18 BULLETIN 183, U. S. DEPARTMENT OF AGRICULTURE. 
with it, and all later progress in conversion is made from it toward 
the distal end of the grain. 
The embryo is able to feed upon starch substituted for its normal 
endosperm. Living embryos are able to grow when grafted on 
endosperms which have been previously killed. 
The function of enzym secretion in germination is localized in the 
epithelial layer of the scutellum. Embryos from which this layer 
has been removed are unable to convert starch. 
SOURCE OF CYTATIC AND PROTEOLYTIC FERMENTS. 
The location of the secretion of diastase is not the only point in the 
physiology of the grain upon which investigators have differed. Some 
authorities who have placed this function in the scutellum have 
ascribed the formation of cytase and of the proteolytic enzym to 
other sources. 
With cytase, if the conclusions of the writers be correct, the ques- 
tion is soon settled. If starch conversion starts next to the embryo 
and moves toward the distal end of the grain, cytase must also be a 
product of the epithelial layer. The breaking down of the cell walls 
must always precede the action of diastase. The diastase of digestion 
seems to be unable to pass readily through unmodified cell walls, and 
most certainly the cell walls are not affected much beyond the 
depleted zone. These two enzyms, then, must of necessity not only 
be associated in the changes which occur in the endosperm, but must 
proceed from a common source. 
The proteolytic ferments would appear from analogy to present 
no differences from the other two. Proteolytic action certainly does 
not occur in any part of the endosperm not yet reached by cytase 
and diastase. If the proteolytic ferments are secreted by the aleurone 
layer they do not become operative until the cytase has moved 
forward from the scutellum and has broken down the cell walls. 
This lack of plausibility is not proof, but, on the other hand, there is 
no reason for thinking that there is more than the single source of 
enzymatic secretion. In one or two other grasses any other origin 
than the scutellum is apparently impossible, because the aleurone 
layer is digested almost as readily as the starch endosperm. In these 
cases, at least, the secretion must be a product of the scutellum, and 
in barley every indication short of absolute proof insists on the same 
conclusion. In the opinion of the writers, the scutellum as a feeding 
organ is endowed with all the functions of digestion, being able to 
utilize all foods occurring in its natural storehouse, the endosperm. 
FUNCTION OF THE ALEURONE LAYER. 
These conclusions leave unexplained one very evident fact. The 
aleurone layer is obviously a vital tissue... Its cells are in no way 
simular to those of the starch endosperm beneath it. This marked 
