108 A GRAIN OF BARLEY. 
exist in soils we cannot for the moment stop to consider, 
but it is sufficient for our present purpose to know that the 
fertility of soils to a great extent depends upon the fact of 
their containing such nitrogen capable of ready assimilation. 
Before the seedling plant has developed its roots sufficiently 
to gain the requisite nitrogen from the soil, it must neces- 
sarily be dependent upon the reserve-nitrogen contained in 
the seed. This, as we have already seen in the case of barley, 
is stored up in two distinct parts of the grain, in the aleurone 
cells of the peripheral portion of the endosperm, and as 
residual protoplasm in the starch-containing cells. 
The nitrogenous substances, like starch, are non-diffusible, 
and must be chemically changed before they can pass through 
their containing cell-walls and reach the growing embryo. 
That they readily do this can be experimentally proved beyond 
all doubt. I have found for instance, by direct determination 
of nitrogen in the growing embryo and in the endosperm, 
that during eleven days germination of barley, 40 per cent. of 
the total reserve nitrogen originally present in the endosperm 
passes through the scutellum to the young growing plant. 
In the case of barley we have at present but little positive 
information as to the way in which the reserve proteids are 
broken down and rendered capable of diffusing through the 
cell-walls. Considerable advances have, however, been made 
in our knowledge of similar phenomena attending the germina- 
tion of certain leguminous plants, and these clearly indicate 
the agency of a ferment somewhat analogous to the pan- 
creatic ferment of animals. 
The pancreatic ferment is instrumental in the processes -of 
animal digestion in breaking down the complex albuminous 
substances into the comparatively simple and readily diffusible 
amido-bodies, ¢.g., leucin and tyrosin-——these bodies readily 
contributing to the building up of protoplasm, and the conse- 
quent formation of new tissue. In those seeds in which the 
agency of some such ferment as this has been. proved to 
take part it has been shown to be present in the form of 
EVD ta Le Bets 
rs 
