noun
definition
The structure in a plant that develops into a seed after fertilization; the megasporangium of a seed plant with its enclosing integuments.
definition
An immature ovum in mammals.
Examples of ovule in a Sentence
The result of fertilization is the development of the ovule into the seed.
The pistil consists of a single carpel with its ovary, style, stigma and solitary ovule or twin ovules.
An ovule consists of a conical nucellus surrounded by a single integument.
The ovule is attached to the placenta, and destined to become the seed.
The part by which the ovule is attached to the placenta or cord is its base or hilum, the opposite extremity being its apex.
The ovule appears at first as a small cellular projection from the placenta.
The micropyle indicates the organic apex of the ovule.
The ovule is curved upon itself, so that the micropyle is near the funicle.
The ovule is sometimes embedded in the placenta, as in Hydnora.
When the ovule is so developed that the chalaza is at the hilum (next the placenta), and the micropyle is at the opposite extremity, there being a short funicle, the ovule is orthotropous.
Then if a second integument be formed it covers all the free part of the ovule, but does not form on the side to which the raphe is adherent.
These may be taken as the three types of ovule; but there are various intermediate forms, such as semi-anatropous and others.
When there is a single ovule, with its axis vertical, it may be attached to the placenta at the base of the ovary (basal placenta), and is then erect, as in Polygonaceae and Compositae; or it may be inserted a little above the base, on a parietal placenta, with its apex upwards, and then is ascending, as in Parietaria.
Sometimes a long funicle arises from a basal placenta, reaches the summit of the ovary, and there bending over suspends the ovule, as in Armeria (sea-pink); at other times the hilum appears to be in the middle, and the ovule becomes horizontal.
The connexion between the base of the ovule and the base of the nucellus is kept up by means of the raphe r.
Consequent upon this, after a longer or shorter period, those changes commence in the embryo-sac which result in the formation of the embryo plant, the ovule also undergoing changes which convert it into the seed, and fit it for a protective covering, and a store of nutriment for the embryo.
Nor are the effects of fertilization confined to the ovule; they extend to other parts of the plant.
The sporangium is attached to the enlarged distal end of its pedicel, from which it hangs down, so as to suggest an anatropous ovule on its funiculus.
Nucellus of an ovule; p.c, pollen-chamber; s, canal leading to p.c; p, pollen-grains in p.c; p', do.
It is the male element which fertilized the ovule.
This grows down through the style until it reaches an ovule.
Eventually the tip of the pollen tube finds its way through the small hole in the integuments surrounding the ovule and penetrates it.
For instance, it has been pointed out in the article on the reproduction of plants that the effect of the fertilization of the female cell in the ovule of a phanerogam is not confined to the female cell, but extends more or less widely outside it, inducing growth and tissue-change.
This is often coloured, is of a denser texture than the surrounding tissue, and is traversed by fibrovascular bundles, which pass from the placenta to nourish the ovule.
The other fuses with genetic material in the ovule to produce a triploid tissue (has three copies of each chromosome).
The fertile leaves or sporophylls are generally aggregated on special shoots to form rioweN which may contain one or both kinds The microspores are set free from the sporangiurn and carried generally by wind or insect agency to the vicinity of the macrospore, which never leaves the ovule.
After fertilization the female cell, now called the oospore, divides and part of it develops into the embryo (new sporophyte), which remains dormant for a time still protected by the ovule which has developed to become the seed.
The male gametophyte is sometimes represented by a transitory prothallial cell;, the two male cells are carried passively down into the ovary and into the mouth of the ovule by means of the pollen-tube.
The ovule develops into the seed; and the gynaeceum and even more remote parts of the flower, develop into the fruit.
Each carpel becomes divided by a median constriction in four portions, each containing one ovule; the style springs from the centre of the group of four divisions.
The eggs are deposited in the ovary-wall, usually just below an ovule; after each deposition the moth runs to the top of the pistil and thrusts some pollen into the opening of the stigma.
In the male flowers, which are numerous, the stamens are sixteen in number and arranged in pairs; the female flowers are solitary, with traces of stamens, and a smooth ovary with one ovule in each of the eight cells - the ovary is surmounted by four styles, which are hairy at the base.
The general view was, that the embryo originated in the ovule, which was in some obscure manner fertilized by the pollen.
The latter traced the tubes as far as the nucleus of the ovule.
When placed on the stigma, under favourable circumstances, the pollen-grain puts forth a pollen-tube which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the mouth of an ovule.
The development of the ovule, which represents the embryo- Gymnosperms; when mature it consists of one or two sac. coats surrounding the central nucellus, except at the apex where an opening, the micropyle, is left.
In Casuarina, Juglans and the order Corylaceae, the pollen-tube does not enter by means of the micropyle, but passing down the ovary wall and through the placenta, enters at the chalazal end of the ovule.
If in its extension to contain the new formations within it the embryo-sac remains narrow, endosperm formation proceeds upon the lines of a cell-division, but in wide embryo-sacs the endosperm is first of all formed as a layer of naked cells around the wall of the sac, and only gradually acquires a pluricellular character, forming a tissue filling the sac. The function of the endosperm is primarily that of nourishing the embryo, and its basal position in the embryo-sac places it favourably for the absorption of food material entering the ovule.
Dorsiventrality is also clearly derived from radial construction, and anatropy of the ovule has followed atropy.
In a few cases two whorls of stamens are present, with three members in each, but generally only three are present; the pistil consists of three or two carpels, united to form an ovary bearing a corresponding number of styles and containing one ovule.
Brown's views as to the structure of the unimpregnated ovule (with the introduction of the term "sac embryonnaire"); and in that it shows how nearly Brongniart anticipated Amici's subsequent (1846) discovery of the entrance of the pollen-tube into the micropyle, fertilizing the female cell which then develops into the embryo.
The ovary is small, rounded to elliptical, and one-celled, and contains a single slightly bent ovule sessile on the ventral suture (that is, springing from the back of the ovary); the micropyle points downwards.
On the other, posterior, side of the grain is a more or less evident, sometimes punctiform, sometimes elongated or linear mark, the hilum, the place where the ovule was fastened to the wall of the ovary.
Before following the growth of the pollen-grain after pollination, we will briefly describe the structure of a cycadean ovule.
A young ovule consists of a conical nucellus surrounded by a single integument terminating as a two-lipped micropyle.
The endosperm detached from a large Ginkgo ovule after fertilization bears a close resemblance to that of a cycad; the apex is occupied by a depression, on the floor of which two small holes mark the position of the archegonia, and the outgrowth from the megaspore apex projects from the centre as a short peg.
Each ovule is enclosed at the base by an envelope or collar homologous with the lamina of a leaf; the fleshy and hard coats of the nucellus constitute a single integument.
The stalk of an ovule, considerably reduced in normal flowers and much larger in some abnormal flowers, is homologous with a leaf-stalk, with which it agrees in the structure and number of vascular bundles.
Secretory sacs occur abundantly in the leaflamina, where they appear as short lines between the veins; they are abundant also in the cortex and pith of the shoot, in the fleshy integument of the ovule, and elsewhere.
A, Peduncle; b, scaly bud; the more internal part of B, leaf bearing marginal ovule.