THE SEED 
io 5 
advantage, but is more suited to withstand unfavourable 
conditions of climate, temperature, drought, &c. Many 
seeds have additional mechanical arrangements facilitating 
transport. 
The fertilised ovum gives rise to the embryo or young 
plant contained in the seed. This (Fig. i, p. 37) consists of 
a short axis, the hypocotyl , bearing at its upper end the apical 
bud of leaves ( plumule ) and one or more seed-leaves or 
cotyledons which do not form part of the bud, but are already 
comparatively well-developed. At the lower end the hypo- 
cotyl bears the radicle or apex of the future root, which 
usually faces and is close to the micropyle of the seed. The 
embryo-sac with its contained endosperm usually increases 
at the expense of the nucellus and consumes the whole 
of the latter tissue. The embryo, meanwhile, treats the 
endosperm in the same way. The integuments ripen into 
the seed-coat or testa. Two cases are to be distinguished in 
the ripe seed. If the embryo in its growth consumes all 
the tissue within the seed-coat and comes into uninterrupted 
contact with it, the seed is exalbuminous , or has no endo- 
sperm (‘albumen’), as inCruciferae, Compositae, Leguminosae, 
&c. If there is any tissue within the testa not forming part 
of the embryo, the seed is albuminous. The tissue may be 
endosperm only, as in Ranunculaceae, Liliaceae, &c. ; this is 
the most common case ; or it may be perisperm (the nu- 
cellar tissue, usually increased by subsequent growth), as in 
Nymphaeaceae, Piperaceae, &c. Usually there is endosperm 
as well as perisperm, when the latter is present. The seed- 
ling must at first depend upon stored food-materials for its 
growth, until its own vegetative organs are in active order, 
and so there is always a store of reserves in a seed, either in 
the embryo (chiefly the cotyledons) or outside it, or both. 
Descriptive Terms, The seed is usually mentioned after the 
fruit in technical descriptions. In form, &c. it may be large or small ; 
spherical, ellipsoidal, &c. ; anatropous, amphitropous, &c. like the 
original ovule. The testa may be smooth, or covered with small or 
large tubercles, papillae, granules, ribs, &c. ; green, brown, or of other 
colours; thin or thick, woody (as in Bertholletia), with a fleshy outer 
layer (as in Bixa, Magnolia, Moraea, Cycas, &c.), hooked or winged 
(see below), or provided with hairs. It is usually firm and tough, 
allowing very little evaporation of water from the seed. Its outer cells 
sometimes have mucilaginous walls and swell when wetted, as in Linum, 
