125 
the Grain of Wheat (Triticum vulgar e). 
that the growth of the tissue keeps pace with the expansion of the embryo- 
sac for some time. At this stage the appearances indicate that this layer 
may persist in the ripe seed in the form of the aleurone layer, but later 
sections do not bear this out. The epidermis continues apparently unaltered 
for some days after the rest of the thin-walled nucellus has been absorbed 
by the developing endosperm. About a fortnight after pollination, however 
the epidermal cells lose their contents, just about the same time that the 
aleurone layer comes into evidence, and the cells get crushed, though the 
outer and inner walls thicken up and persist in the ripe seed (13). 
(c) Endosperm. 
i. Development. It has already been shown that the endosperm arises 
in the first place by free cell formation, i.e. a large number of nuclei are 
derived from the definitive nucleus by repeated division, and are embedded 
in the protoplasm lining the wall of the embryo-sac, no cell walls being 
formed. During this period the protoplasm seems to be more dense in the 
immediate neighbourhood of the disorganizing antipodal cells, possibly 
because, as Koernicke (8) suggests, the developing endosperm is drawing 
very largely on the substance of the antipodal tissue for its own nutrition. 
The surrounding nucellar tissue, with the exception of its epidermis or 
limiting layer, is gradually absorbed, except in the immediate neighbourhood 
of the fertilized ovum, in which position there is also a large accumulation 
of protoplasm with many embedded nuclei. 
About seven or eight days after pollination a change occurs and the 
formation of cell walls begins. These start at the periphery of the en- 
dosperm and develop inwards very rapidly, till within about two days the 
endosperm is changed from a mere nucleated protoplasmic layer surrounding 
a large central vacuole to a definite tissue extending through practically the 
whole of the embryo-sac. The central vacuole of the embryo-sac fills up 
first with endosperm tissue at the micropylar end (7), though some sections 
seem to indicate that the cytoplasm immediately surrounding the embryo 
does not develop its cell walls till a little later. At first the mass of cyto- 
plasm completely surrounds the young embryo except just at the tip, but 
as the latter develops it gradually absorbs the endosperm on the outer side 
away from the furrow, and also the nucellar tissue in the same region, so 
that it is displaced from its central position to a somewhat lateral one on 
the outer side of the endosperm. Eventually walls are developed all the 
way through, but the cells formed from the cytoplasm in the neighbourhood 
of the embryo retain their dense protoplasmic contents for a long time after 
the main mass of endosperm tissue begins to appear very poor in proto- 
plasm. Westermaier (1 1) describes a similar phenomenon as occurring in 
Zea mais. 
Quite early in development the endosperm cells on the ventral side 
