plants the nucellus is not thus absorbed, but itself becomes a seat of
deposit of reserve-food constituting the _perisperm_ which may coexist
with endosperm, as in the water-lily order, or may alone form a
food-reserve for the embryo, as in _Canna_. Endospermic food-reserve
has evident advantages over perispermic, and the latter is
comparatively rarely found and only in non-progressive series. Seeds
in which endosperm or perisperm or both exist are commonly called
_albuminous_ or _endospermic_, those in which neither is found are
termed _exalbuminous_ or _exendospermic_. These terms, extensively
used by systematists, only refer, however, to the grosser features
of the seed, and indicate the more or less evident occurrence of a
food-reserve; many so-called exalbuminous seeds show to microscopic
examination a distinct endosperm which may have other than a nutritive
function. The presence or absence of endosperm, its relative amount
when present, and the position of the embryo within it, are valuable
characters for the distinction of orders and groups of orders.
Meanwhile the ovary wall has developed to form the fruit or pericarp,
the structure of which is closely associated with the manner of
distribution of the seed. Frequently the influence of fertilization is
felt beyond the ovary, and other parts of the flower take part in
the formation of the fruit, as the floral receptacle in the apple,
strawberry and others. The character of the seed-coat bears a definite
relation to that of the fruit. Their function is the twofold one of
protecting the embryo and of aiding in dissemination; they may also
directly promote germination. If the fruit is a dehiscent one and the
seed is therefore soon exposed, the seed-coat has to provide for the
protection of the embryo and may also have to secure dissemination. On
the other hand, indehiscent fruits discharge these functions for the
embryo, and the seed-coat is only slightly developed.