from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A cell that arises from a primordial germ cell and differentiates into an oocyte in the ovary.
- n. A female reproductive structure in certain thallophytes, usually a rounded cell or sac containing one or more oospheres.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. An immature ovarian egg within a developing fetus
from the GNU version of the Collaborative International Dictionary of English
- n. A special cell in certain cryptogamous plants containing oöspheres, as in the rockweeds (Fucus), and the orders Vaucherieæ and Peronosporeæ.
from The Century Dictionary and Cyclopedia
- n. In botany, the female sexual organ in certain cryptogamic plants.
- n. In zoology: The primordial mother-cell which gives rise to the ovum and its follicle.
- n. One of the youngest ovarian cells, characterized by having in its nucleus the same number of chromosomes as in the nuclei of the somatic or body-cells. The oögonia, which eventually give rise to the primary oöcytes, are homologous in the oögenesis with the spermatogonia in the spermatogenesis of the male animal of the same species.
The female reproductive structure (oogonium) of a charophyte.
The formation of these follows the same course as that above described for the polysporic oogonium, with certain necessary simplifications.
Antheridia clavate, one, or rarely more, on each oogonium, usually arising just below its basal wall, rarely of diclinous origin.
In case of the androgynous species, the antheridial branches begin to appear soon after the oogonial ones (Fig. 21); but the antheridia have usually been formed and come into contact with the oogonium before the basal wall of the latter has appeared.
The number of antheridia attached to a single oogonium shows very little tendency to definiteness, except in A. racemosa (Fig. 94).
The num - ber of these nuclei bears no relation to the number of oospheres to be formed, except as both are controlled by the amount of protoplasm in the oogonium.
B. Oddpore single, wholly filling the oogonium LeptoUgnia. oospores one or more, not wholly filling the odgonium Saprolbonia.
Mor - phologically sexual reproduction by oospores developed in typically globular oagouia, one or more from the entire protoplasm of each oogonium; antheridia on branches of androgynous or diclinous origin, very rarely on the oogonial branch, uniting with all, or with only a part of the oiigonia, or in several species wholly absent; when present, usually producing fertilization tubes which remain closed, at least in some species.
Oospores one or two in an oogonium; hy phse slender S.asteboprora. oospores several in an oogonium; hypbcB very stout » 8.
After the growth of the oogonium has ceased and the protoplasm has become parietal in position, the outer walls thicken and the basal wall is formed, as already described.