THE SEED. 
07 
Likewise in the nucellus, changes are also taking 
place ; the cells are found to be dividing, and stor- 
ing starch, oil, aleurone and other food materials, 
like the cells of the embryo sac. The reserve cells of 
the nucellus constitute the perisperm, while those 
formed in the embryo sac make up the endosperm. 
Usually the endosperm of seeds is prominently de- 
veloped while the perisperm occurs as a thin layer ; in 
cardamom, however, the endosperm and perisperm are 
both well developed. In some instances the embryo 
may not fill the embryo sac, as in cocoanut, and some 
times, as in the almond, both of the reserve layers are 
consumed in the development of the embryo. 
The perisperm and endosperm are sometimes spoken 
of as constituting the albumen of the seed, but as the 
cells comprised in these layers contain not only organ- 
ized contents and aleurone grains, but starches, oils 
and other substances, the term is misleading. On this 
basis, seeds containing either endosperm or perisperm, 
or both, have been designated as albuminous, but on 
account of these layers containing larger proportions 
of other substances than proteids it would be better to 
speak of them as reserve layers. 
While these changes in the nucellus and embryo sac 
have been going on there have been equally great 
changes in the coats of the ovules, which later consti- 
tute the seed - coats. In the seed the two coats are 
generally readily distinguishable: the inner, as in 
ricinus, pepo, etc., is thin, light in color and of a 
delicate structure, and is known as the tegmen or en- 
dopleura ; the outer is more or less thickened, of a 
darker color and firmer in structure, and is known as 
the testa, spermoderm or episperm. In some instances 
the perisperm, or both perisperm and endosperm, may 
be reduced to a thin layer and be considered as form- 
