32 Humphrey . — - The Development of the 
It is apparently by the breaking up of these empty cells that 
the exocarp is separated from the endocarp. The exocarp 
forms a firm and dry envelope about the seed, showing no 
pulpy consistency. At a pretty early stage the line of demar- 
cation between exocarp and endocarp may be traced (Fig. 62) 
around the loculus, extending downward at the base to or 
just below the point of origin of the very short funiculus. 
Since the cleft which separates the funiculus from the ovarian 
wall extends farther downward on the side of the micropyle 
than on that of the raphe, the plane of the end of the 
endocarp is very oblique to the axis of the ovule. The 
abrupt termination of the endocarp in this region leaves at 
the micropylar end of the seed an unprotected circular area 
enclosed by its rounded end. This area is originally occupied 
by the soft parenchyma of the funiculus, which is pierced by 
the vascular bundle ( v . b., Fig. 64). After the seed has 
reached its full size and the endocarp is well formed, a 
differentiation begins in this tissue. The cells in an oblique 
band extending across the open mouth of the endocarp, just 
within its end (Fig. 68), begin rapidly to thicken their walls, 
and soon the mouth is filled by a thick plug of stone-cells 
thus formed [set. p., Fig. 69). When the seed is separated 
from its attachments the break occurs at the outer surface 
of this plug. It is probable that, in germination, it serves 
as a germinal lid, being pushed out by the growing embryo, 
while the end of the endocarp forms a firm collar about the 
neck of the absorbing organ. 
The characteristic micropylar pad continues to enlarge 
(in. /., Figs. 66, 68) until the seed reaches its adult size, 
and then suffers considerable reduction by compression (m. 
Fig. 69). With the growth of the embryo-sac, the tissue of 
the nucellus is steadily reduced until only a narrow band 
next to the integument remains. This never becomes wholly 
obliterated, but remains as a distinct starch-bearing perisperm 
(ps. /., Figs. 68, 69, 70). The walls of the embryo-sac 
become lined by a protoplasmic layer with free nuclei (esp., 
Fig. 67), from which an endosperm-tissue develops in the 
