94 Oliver . — On the Structure , Development, 
The embryo, meanwhile, has been developing. In Figure 30 
the suspensor has elongated, and the embryonic cell has been 
carried down and become immersed in the endosperm. 
There is no point of special interest in its mode of segmenta- 
tion. The developing embryo gradually encroaches upon 
the endosperm, which it absorbs. Soon after the stage 
represented in Fig. 36, the two cotyledons are differentiated 
(Fig. 46) and the arrangement of tissues at the root-apex is 
that obtaining in the adult root. The root end is gradually 
brought higher up towards the micropylar end of the embryo- 
sac (Fig. 27), and the shoot end (with the cotyledons), to the 
base of the seed, so that ultimately only a narrow layer of 
endosperm remains between the cotyledons and the appendage 
(Fig. 35). In Figure 47, the arrangement of the tissues of 
the young root-apex is well shown. This apex is from an 
embryo of about the same age as Fig. 46. There is an inde- 
pendent plerome (pi), and a periblem ( pb .) arising from a 
single layer of cells. Outside, and independent of this, is the 
dermato-calyptrogenic layer (d.cl). At the apex the suspensor 
( sp .) is attached. Essentially the same arrangement is re- 
tained in the ripe seed (Fig. 37), though here the tip of the 
radicle is very much wider, and the number of cells formed 
from the three initial groups much greater. 
In the ripe seed there is a considerable width of endosperm 
remaining (some six or eight layers), the cells of which are 
stored with aleurone-grains and oil-droplets. It is not sur- 
prising that the seed was originally described as being 
‘exalbuminous,’ for the tissues of the integument are, in the 
ripe seed, reduced to a single layer of cells ( — testa), so that 
without embryological evidence it would be impossible to 
regard what I find to be endosperm, as other than integument. 
In Pedalium even — usually described as exalbuminous — I find 
also several layers of true endosperm, almost as much as in 
Trapella . 
With the ripening of the seed the suspensor is gradually 
obliterated ; the walls of that part which runs through the 
synergidal tubercle become pressed together, so that only 
