134 THE FLOWERING PLANT. 
which is a brown layer covering the edible endosperm, here form- 
ing a relatively thin layer surrounding a milk-containing cavity. 
At one end of the cocoa-nut 
are three round marks. One 
of these corresponds to a soft 
part adjoining the micropyle 
of the seed. The minute em- 
bryo is to be found imbedded 
in the endosperm at this point. 
The various parts of the seed 
are subject to considerable 
variation, as the above ex- 
amples show. Straight, bent, 
and inverted ovules develop 
into similarly termed seeds 
(cf. p. 104). The seed-coat is 
of one or two layers, according 
to the number of integuments 
possessed by the ovule. It 
frequently happens that out- 
growths from the seed-coat or 
FIG. 54.—Longitudinal Section of a Fruit 
These 
(grain) of Maize (Zea Mais), X 4 [from Sachs]. 
c. pericarp; n. remains of style; js. attached 
base of fruit; eg. dense yellow endosperm, 
between which and the pericarp is seen the 
seed-coat; ew. loose white endosperm; sc. 
scutellum of embryo, its continuation can 
be traced round the embryo below; ss. its 
apex ; e. its epidermis (shaded like seed-coat) 
on endosperm side; k&. plumule; w. (below) 
radicle, tipped by root-cap; ws. its root- 
sheath ; w. (above) adventitious roots arising 
from embryonic stem. Vascular bundles, 
white (note pith in vascular cylinder of radi- 
funicle are present. 
constitute an aril, which may 
consist of hairs only, as in 
cotton, willow-herb, and wil- 
low; or it may be a knob 
(castor-oil seed), ridge, crest, 
or complete extra covering. 
Examples of the last kind are 
seen in the red fleshy cup en- 
cle, as well as in stem). ° ° 
closing the solitary seed of 
yew, the loose orange-coloured investment of spindle-tree seeds, 
and ‘“‘mace” which surrounds the nutmeg. 
Both in albuminous and exalbuminous seeds, but especially in 
the latter, the embryo may be packed away in the most various 
manners. The cotyledons particularly are often folded, rolled, or 
crumpled in an elaborate way. 
Little need be said here about the minute structure of the 
seed. It is enough to state that reserve materials are laid up in 
the albumen (or cotyledons if this is absent) under three chief 
forms: (1) starch grains; (2) aleurone grains, which are minute 
masses of proteid matter, often containing crystalloids (cf. p. 26) ; 
(3) oily matters ; (4) cellulose. The date is an example of (4) ; 
and oily seeds, such as brazil-nut and castor-oil, of (3). Alewrone 
grains are commonest and largest in oily seeds. A thin section, 
