THE SEED. 
99 
cells, (3) a pigment layer, (4) one or two rows of paren- 
chymatous cells, (5) a row of more or less obliterated 
parenchyma cells. 
The epidermal cells vary considerably in different 
species, both as regards the form of the cells and the 
composition of the walls ; the cells may be more or less 
isodiametric in cross section, as in cardamom ; ellipti- 
cal, as in almond ; palisade-like, as in Abrus precatorius, 
or more or less irregular, as in Delphinium. While 
the outer and side walls are usually thickened, in hyos- 
cyamus it is the inner and side walls which are thick- 
ened, the outer wall remaining thin. The outer wall 
may be in part modified to mucilage, as in mustard 
and flaxseed ; or to non-secreting hairs which consist 
either of cellulose, as in cotton, or lignocellulose, as in 
nux vomica. 
The perisperm and endosperm consist chiefly of paren- 
chyma cells, which contain, besides the organized 
contents, starch, as in physostigma; oil, as in strophan- 
thus; aleurone grains, as in ricinus; glucosides, as 
in almond ; alkaloids, as in stramonium. The walls 
are usually thin, but may in some instances be consid- 
erably thickened, as in coffee, colchicum and nux 
vomica. 
In the fully developed embryo three distinct parts 
may be differentiated : (1) the cotyledons; (2) the part 
below the cotyledons, known as the hypocotyl, the 
apical portion of which constitutes the root-like portion 
or radicle; (3) the part above the cotyledons, known 
as the epicotyl, the apex of which consists of a more or 
less developed bud spoken of as a plumule. 
The position of the embryo in the seed varies some- 
what: in most seeds it lies in the center, as in stro- 
phanthus and linum ; it may, however, be excentral, as 
in colchicum and nutmeg. The cotyledons are usually 
