A GRAIN OF BARLEY. 105 
This is in the closest possible contact with several layers of 
compressed and empty cells of the endosperm, whose existence 
calls for a word of explanation. During the later stage of 
the development of the contents of the embryo-sac, which 
comprehend, you will remember, both embryo and endosperm, 
the development of the embryo goes on at the expense of 
some portion of the starch-containing cells of the endosperm. 
As these are emptied of their contents, they are gradually 
compressed by the expanding embryo, and we find them in 
the ripe grain as we have them depicted here. 
The portion of the embryo furnished with this palisade-like 
epithelium is known as the scutellum, or “little shield” of 
the embryo, and it is manifest that the nutritive contents of 
the endosperm, in order to be of any use to the embryo, 
must pass through the layers of compressed empty cells, and 
the epithelium of the scutellum. The cell-walls of all these 
tissues, and of the cells containing the reserve starch and 
proteids, have no apertures of any kind in their substance, 
and it now becomes necessary to consider how, under these 
apparently difficult circumstances, the solid reserve material can 
find its way to the embryo. 
In the first place, it is manifest that these solid reserve 
bodies must pass through the cell walls in the state of solu- 
tion; but although starch and proteids are, under favourable 
circumstances, to some extent soluble in water, they belong 
to a class of bodies incapable of readily passing through a 
moist membrane; they are, in other words, very won-diffusible. 
To bring them into a state in which they can readily pass 
through even a thin cell wall, they must undergo very con- 
siderable chemical alteration. In all germinating seeds we 
find that great chemical changes take place in the reserve 
materials, under the influence of warmth, moisture, and access 
of air, and it is to these that I must now briefly draw your 
attention. : 
We perhaps know more about the transformation of the 
important reserve material s¢avch than any of the others, and 
