vill] FERTILISATION 121 
When the pollen-grain, having adhered to the hairy 
stigma, has begun to germinate, the resulting pollen-tube 
creeps down between the cells 
of the stigma, and hands over 
its enclosed nuclei to the em- 
bryo-sac, where fertilisation of 
the egg-cell is accomplished, 
by the fusion of one of the 
pollen nuclei with the nucleus 
of the egg-cell. As the result- 
ing embryo developes, the sac 
becomes filled with endosperm- 
cells charged with  starch- 
grains or sugar, and in the 
ripe seed the embryo is always 
found affixed laterally and be- 
low to this endosperm—a point 
of distinction from Sedges, 
where the embryo is buried 
in the endosperm. 
The ripe seed fills the 
ovary, and its outer walls 
usually fuse with those of 
the carpel, forming the well- 
known Caryopsis or “ grain.” 
If such a “ grain” is care- 
fully examined, three chief 
parts are visible in addition 
to the embryo. (Fig. 38.) 
Fig. 38. Longitudinal median 
section of the caryopsis of a 
grass—e.g. Lolium (x about 
35). p, pericarp; t, attach- 
ment to axis; m, position of 
micropyle; H, endosperm ; A, 
its aleurone layer; J, folded 
leaves of plumule; 7, radicle; 
r’’, secondary roots; RC, root- 
cap; s, scutellum. The dark 
line e represents the surface 
where the face of the scu- 
tellum is applied to the endo- 
sperm and where absorption 
of the lutter takes place. 
Firstly, we find on the outside the fused seed- and fruit- 
