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.
serere, to sow), the fertilized ovule of plants.
The ovule appears at first as a small cellular projection from the placenta.
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.
A young ovule consists of a conical nucellus surrounded by a single integument terminating as a two-lipped micropyle.
The solitary ovule springs erect from the base of the ovarian cavity.
Part of Ovule in longitudinal section.
These, as in Gymnosperms, are of two kinds, microspores or pollen-grains, borne in the stamens (or microsporophylls) and megaspores, in which the egg-cell is developed, contained in the ovule, which is borne enclosed in the carpel (or megasporophyll).
Apex of Ovule, and Pollen-grain.
The developing embryo at the end of the suspensor grows out to a varying extent into the forming endosperm, from which by surface absorption it derives good material for growth; at the same time the suspensor plays a direct part as a carrier of nutrition, and may even develop, where perhaps no endosperm is formed, special absorptive "suspensor roots" which invest the developing embryo, or pass out into the body and coats of the ovule, or even into the placenta.
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 micropyle indicates the organic apex of the ovule.
In other species the infection occurs through the style of the flower, but the fungus after reaching the ovule develops no further during that year but remains dormant in the embryo of the seed.
In Cycas the altered leaf, upon the margin of which the ovule is produced, and the peltate scales, from which they are pendulous in Zamia, are regarded by all botanists as carpellary leaves.
The ovule is not enclosed in an ovary, and the usually solitary macrospore becomes filled with a prothallus, in the upper part of which are formed several rudimentary archegonia.
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.
I12), Cistaceae, and most gymnosperms. In such an ovule a straight line drawn from the hilum to the micropyle passes along the axis of the ovule.
I I 1) is the commonest form amongst angiosperms. In this ovule the apex with the micropyle is turned towards the point of attachment of the funicle to the placenta, the chalaza being situated at the opposite extremity; and the funicle, which runs along the side usually next the placenta, coalesces with the ovule and constitutes the raphe (r), which often forms a ridge.
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.
The position of the ovule relative to the ovary varies.
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.
- Campylotropous ovule of wall-flower (Cheiranthus), showing the funicle f, which attaches the ovule to the placenta; p, the outer, s, the inner coat, n, the nucellus, ch, the chalaza.
The ovule is curved upon itself, so that the micropyle is near the funicle.
- Anatropous ovule of Dandelion (Taraxacum), nucellus, which is inverted, so that the chalaza ch, is removed from the base or hilum h, while the micropyle f is near the base.
The connexion between the base of the ovule and the base of the nucellus is kept up by means of the raphe r.
112), through the conducting tissue of the style when present, and reach the interior of the ovary in angiosperms, and then pass to the micropyle of the ovule, one pollen-tube going to each ovule.
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.
bundles in tangential section; br, bracts; d, short axillary shoot, bearing a bracteole and a terminal ovule; i, integument; n, nucellus of ovule; ov, another ovule seen from the outside.
Nucellus of an ovule; p.c, pollen-chamber; s, canal leading to p.c; p, pollen-grains in p.c; p', do.
32, A, it appears that each ovule was borne terminally, on an extremely short axillary shoot, as in Taxus among recent Gymnosperms. The ovule consists of an integument (regarded by some writers as double) enclosing the nucellus.
15, 4 and 7), as investigated in English, French, Italian, and American specimens, may be briefly described as a short lateral shoot or peduncle, arising in a leaf-axil and terminating in a bluntly rounded apex, bearing numerous linear bracts enclosing a central group of appendages, some of which consist of slender pedicels traversed by a vascular strand and bearing a single terminal ovule enclosed in an integument, which forms a distal canal or micropyle.
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.
- In fertilization - the influence in flowering plants of the male-cell in the pollen tube upon the eggcell in the ovule (see Botany) - there are many circumstances of importance horticulturally, to which, therefore, brief reference must be made.
The ordinary type of female flower has the form of a long, naked peduncle a ' -Ã‚°' ` bearing a single ovule on "i, rll?li either side of the apex (fig.
The facts on which this description is based are derived partly from anatomical evidence, and in part from an account given by a Japanese botanist, Fujii, of several abnormal female flowers; in some cases the collar at the base of an ovule, often described as an arillus, is found to pass gradually into the lamina of a leaf bearing marginal ovules (fig.
A pollen-grain when first formed from its mother-cell consists of a single cell; in this condition it may be carried to the nucellus of the ovule (e.g.
In each ovule one megaspore comes to maturity, but, exceptionally, two may be present (e.g.
Several embryo-sacs (megaspores) are present in the nucellus of a young ovule, but one only attains full size, the smaller and partially developed megaspores (fig.
The ovule is attached to the placenta either directly, when it is sessile, or by means of a prolongation funicle (fig.
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.
Where, by more rapid growth on one side than on the other, the nucellus, together with the integuments, is curved upon itself, so that the micropyle approaches the hilum,and ultimately is placed close to it, while the chalaza is at the hilum, the ovule is campylotropous (fig.
The inverted or anatropous ovule (fig.
The anatropous ovule arises from the placenta as a straight or only slightly curved cellular process, and as it grows, gradually becomes inverted, curving from the point of origin of the integuments (cf.
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.
1) having a thin outer skin (epicarp) enclosing the flesh of the peach (mesocarp), the inner layers of the carpel becoming woody to form the stone, while the ovule ripens into the kernel or seed.
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.
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.
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.
Abies), on each side of which is situated an inverted ovule, consisting of a nucellus surrounded by a single integument.
The female flowers of the Taxaceae assume another form; in Microcachrys (Tasmania) the reproductive structures are spirally disposed, and form small globular cones made up of red fleshy scales, to each of which is attached a single ovule enclosed by an integument and partially invested by an arillus; in Dacrydium the carpellary leaves are very similar to the foliage leaves - each bears one ovule with two integuments, the outer of which constitutes an arillus.
One argument that has been adduced in support of the axillary bud theory is derived from the Palaeozoic type Cordaites, in which each ovule occurs en an axis borne in the axil of a bract.
Without expressing any decided opinion as to the morphology of the double cone-scale of the Abietineae, preference may be felt in favour of regarding the cone-scale of the Araucarieae as a simple carpellary leaf bearing a single ovule.
The ovule is usually surrounded by one integument, which projects beyond the tip of the nucellus as a wide-open lobed funnel, which at the time of pollination folds inwards, and so assists in bringing the pollen-grains on to the nucellus.
The female flower is enveloped in a closely fitting sac-like investment, which must be regarded as a perianth; within this is an orthotropous ovule surrounded by a single integument prolonged upwards as a beak-like micropyle.
The flower may be described as a bud bearing a pair of leaves which become fused and constitute a perianth, the apex of the shoot forming an ovule.
In function the perianth may be compared with a unilocular ovary containing a single ovule; the projecting integument, which at the time of pollination secretes a drop of liquid, serves the same purpose as the style and stigma of an angiosperm.
The whole flower may be looked upon as an adventitious bud bearing two pairs of leaves; each pair becomes concrescent and forms a perianth, the apex of the shoot being converted into an orthotropous ovule.
Each cone consists of an axis, on which numerous broad and thin bracts are arranged in regular rows; in the axil of each bract occurs a single flower; a male flower is enclosed by two opposite pairs of leaves, forming a perianth surrounding a central sterile ovule encircled by a ring of stamens united below, but free distally as short filaments, each of which terminates in a trilocular anther.
The integument of the sterile ovule is prolonged above the nucellus as a spirally-twisted tube expanded at its apex into a flat stigma-like organ.
A complete and functional female flower consists of a single ovule with two integuments, the inner of which is prolonged into a narrow tubular micropyle, like that in the flower of Gnetum.
In some of the heterosporous forms (Lepidocarpon, Miadesmia) the sporangia were sometimes surrounded by an integument; and since only a single megaspore attained maturity, the structure of the megasporangium suggests a comparison with an ovule.
Under natural circumstances wheat is selffertilized: that is to say, the pollen of any given flower impregnates the stigma and ovule of the same flower; the glumes and coverings of the flower being tightly pressed round the stamens and stigmas in such a way as to prevent the access of insects and to ensure the deposit of the pollen upon the stigmas of the same flower.
- Vertical section of the ovule of the Scotch Fir (Pinus sylvestris) in May of the second year, showing the enlarged embryo-sac b, full of endosperm cells, and pollen-tubes c, penetrating the summit of the nucellus after the pollen has entered the large micropyle.
As the seed develops from the ovule which has been fertilized by the pollen, the essential structures for seed-production are two, viz.
These are with few exceptions foliar structures, known in comparative morphology as sporophylls, because they bear the spores, namely, the microspores or pollen-grains which are developed in the microsporangia or pollen-sacs, and the megaspore, which is contained in the ovule or megasporangium.
The calyx, petals and stamens spring from above the ovary (o) in which two chambers are shown each with a pendulous ovule; d, disc between the stamens and stigmas.
The ovules are attached to the placenta, which consists of a mass of cellular tissue, through which the nourishing vessels pass to the ovule.
f, Funicle or or may be confined to the base or stalk of ovule (ov); pl, plaapex only.
In other instances they rise The ovule.
The ovule is usually contained in an ovary, and all plants in which the ovule is so enclosed are termed angiospermous; but in Coniferae and Cycadaceae it has no proper ovarian covering, and is called naked, these orders being denominated gymnospermous.
- Successive stages in the development of an ovule.
- Orthotropous ovule of Polygonum in section, showing the embryo-sac s, in the nucellus n, the different ovular coverings, the base of the nucellus or chalaza ch, and the apex of the ovule with its micropyle m.
- 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.
106, n), or central cellular mass of the ovule.
This nucellus may remain naked, and alone form the ovule, as in some orders of parasitic plants such as Balanophoraceae, Santalaceae, &c.; but in most plants it becomes surrounded by certain coverings or integuments during its development.
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