A GRAIN OF BARLEY. 99 
cherries, plums, &c., a portion of the walls of the ovary in- 
creases in thickness and becomes very succulent, forming the 
sweet pulpy portion of the fruits. In the Order of Grasses 
the very reverse of this is the case. The walls of the ovary, 
which are comparatively thick, and very soft in the early 
stages of growth, become partially absorbed and highly com- 
pressed as the development of the seed goes on, until finally, 
when the grain has been ripened, the tissues of the ovary are 
represented only by a very thin skin, the fevicarp, covering 
the thin-walled ovule with its contents. 
We. can now turn once more to the sections of ripe barley 
to which I drew your attention earlier in the evening, and I 
think we are now in a better position to understand their 
main features. (See Plate II.) 
First of all our enquiry has taught us that both the germ 
or embryo, and the white starchy matter which form the 
endosperm, and together make up the greater part of the 
contents of the grain, are derived directly from the emdryo- 
sac, which itself sprang from a single cell in the interior of 
the ovule. The extremely thin epidermis of the enlarged 
embryo-sac can still be made out in the ripe barley, as a 
layer of extreme tenuity, in close contact with the square- 
shaped cells which form the outer layer of the endosperm. 
(See Plate II., ef. nue.) 
You will notice in Plate I., Fig. 3 that the endosperm 
itself, owing to the tension to which it has been subjected 
during its growth, has been deeply indented on one side. 
This indentation extends longitudinally the whole length of 
the endosperm, and reaches almost to the centre, giving the 
contents of the grain a two-lobed appearance. The outward 
expression of this indentation is found in the furrow, which is 
so evident on the ventral side of a grain of barley. In the 
deepest portions of this fold in the endosperm lie some 
empty sheaf-like cells, (Fig. 3, 7), the only remnants of the 
nucleus which have escaped absorption by the growing 
~embryo-sac. (Compare Plate III., Fig. 8, pz.) 
