Fig. 394.
Section through nucellus and
upper part of embryo sac of
cotton at time of entrance of
pollen tube. E, egg; S,
synergids; P, pollen tube with
sperm cell in the end. (Duggar.)
660. Seed.—As the embryo is developing it derives its nourishment from the endosperm (or in some cases perhaps from the nucellus). At the same time the integuments increase in extent and harden as the seed is formed.
Fig. 395.
Fertilization of cotton. pt, pollen tube; Sn, synergids; E, egg, with male and female nucleus fusing. (Duggar.)
Fig. 396.
Diagrammatic section of ovary and ovule at time of fertilization in angiosperm. f, funicle of ovule; n, nucellus; m, micropyle; b, antipodal cells of embryo sac; e, endosperm nucleus; k, egg-cell and synergids; ai, outer integument of ovule; ii, inner integument. The track of the pollen tube is shown down through the style, walls of the ovary to the micropylar end of the embryo sac.
661. Perisperm.—In most plants the nucellus is all consumed in the development of the endosperm, so that only minute fragments of disorganized cell walls remain next the inner integument. In some plants, however, (the water-lily family, the pepper family, etc.,) a portion of the nucellus remains intact in the mature seed. In such seeds the remaining portion of the nucellus is the perisperm.