Bot. the female gametophyte of a flowering plant, consisting typically of a microscopic elongated sac that is situated within the ovule and contains eight nuclei in seven cells: it gives rise to the embryo and endosperm of the seed after fertilization
It may be wholly absorbed by the progressive growth of the embryo within the embryo-sac, or it may persist as a definite and more or less conspicuous constituent of the seed.
Ultimately the apex of the tube comes in contact with the tip of the embryo-sac and perforates it.
Ek, Nucleus of embryo-sac. ei, Egg-apparatus.
A pro-embryo - a cellular row of which the cell nearest the micropyle becomes attached to the apex of the embryo-sac, and thus fixes the position of the developing embryo, while the terminal cell is projected into its cavity.
- Vertical section of the ovule of the Austrian Pine (Pinus austriaca), showing the nucellus a, consisting of delicate cellular tissue containing deep in its substance an embryo-sac b.