8 17 
Embryo and A leurone Layer of Horde urn. 
in composition of the medium and oxidation by atmospheric oxygen. The 
relative extent to which these two series of opposed factors operate varies 
with the particular phase of the culture experiment considered. Presumably 
it is most marked during the period 0-3 days; from this period onward 
the relative augmentation of the secretory capacity is well maintained. 
Although in the majority of instances, especially in gelatine media, the 
embryo exhibits good growth accompanied by considerable increase in its 
root and plumular development, there is reason to believe that under these 
conditions development is by no means strictly normal. In particular 
is this reflected on its amyloclastic secretory capacity; the results given in 
the foregoing tables distinctly under-estimate the potentiality of its secretory 
functions. The values of the secretory capacity of the embryo are 
of practically the same order as in the preceding experiments on purely 
artificial media. 
The preliminary treatment to which the barley endosperm substance 
was subjected probably induces changes in it of both a physical and 
a chemical nature which render it less readily attackable by the embryo. 
The experiment furnishes an example of the difficulty of preparing 
a culture substratum which shall serve as an adequate substitute for the 
natural inner endosperm. 
The positive nature of the evidence adduced furnishes direct proof that 
the barley embryo secretes an amyloclastic enzyme. Initially the embryo, 
as stated by Brown and Morris (loc. cit., p. 492) and confirmed by direct 
examination by myself, contains little (not more than 1-2 mg. per 20 
objects) or no pre-existent amylase at the moment of removal from the 
seed at the termination of the steeping operation carried out under the 
conditions described. The amounts of enzyme found in the medium at the 
termination of the cultural experiment therefore represent the magnitude of 
its varying secretory capacity under the conditions of experiment selected. 
IV. Amyloclastic Secretory Capacity of the Aleurone 
Layer of Barley. 
The earlier researches of Brown and Morris ( 1 . c.) indicate that these 
authors regarded the aleurone layer not as a glandular tissue, but as func¬ 
tioning in some serviceable way in the general economy of the seed during 
the later stages of the germinative process. 
It was shown by Haberlandt ( 1 . c.) that the aleurone layer of rye 
possesses amyloclastic secretory powers, and it was suggested by him that 
the possession of this capacity was probably a common attribute of the 
aleurone layer in other members of the Grasses, 
