Botanists were for a long time content to know that the scattering of the pollen from the anther, and its application to the stigma, were necessary for the production of perfect seed, but the stages of the process of fertilization remained unexplored.
- I, anther; 2, pollen grain of Hollyhock (Althaea rosea) enlarged.
The pollen is set free by the opening (dehiscence) of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the heath family (Ericaceae), or by valves, as in the barberry.
In these cases the anther is to a greater or less degree fixed.
A, anther; s, pistil; st, style; v, stigmatic surface.
- Stamen of a species of Nightshade (Solanum), showing the divergence of the anther-lobes at the base, and the dehiscence by pores at the apex.
- The stamen of the Barberry (Berberis vulgaris), showing one of the valves of the anther (v) curved upwards, bearing the pollen on its inner surface.
The endothecium varies in thickness, generally becoming thinner towards the part where the anther opens, and there disappears entirely.
Sometimes the anther has a single cavity, and becomes unilocular, or monothecal, or dimidiate, either by the disappearance of the partition between the two lobes, or by the abortion of one of its lobes, as in Styphelia laeta and Althaea officinalis (hollyhock).
The form of the anther-lobes varies.
That part of the anther to which the filament is attached is the back, the opposite being the face.
The division between the lobes is marked on the face of the anther by a groove or furrow, and there is usually on the face a suture, indicating the line of dehiscence.
The anther-lobes are united to the connective, which is either continuous with the filament or articulated with it.
When the filament is continuous with the connective, and is prolonged so that the anther-lobes appear to be united to it throughout their whole length, and lie in apposition to it and on both sides of it, the anther is said to be adnate or adherent; when the filament ends at the base of the anther, then the latter is innate or erect.
In Stachys the connective is expanded laterally, so as to unite the bases of the anther-lobes and bring them into a horizontal line.
When the anther lobes are rendered horizontal by the enlargement of the connective, then what is really longitudinal dehiscence may appear to be transverse.
The cleft does not always proceed the whole length of the anther-lobe at once, but often for a time it extends only partially.
- Two stamens of Pansy (Viola tricolor), with their two anther-lobes and the connectives (p) extending beyond them.
- Stamen of Lady's Mantle (Alchemilla), with the anther opening transversely.
Sometimes, as in Canna, one of the anther-lobes becomes abortive, and a petaloid appendage is produced.
The pollen-grains or microspores contained in the anther consist of small cells, which are developed in the large thick-walled mother-cells formed in the interior of the pollen-sacs (microsporangia) of the young anther.
C, The one-celled ovary cut a, The anther, con transversely, having three taining pollen parietal placentas.
This column stands up from the base of the flower, almost at right angles to the lip, and it bears at the top an anther, in the two hollow lobes of which are concealed the two pollen-masses, each with its caudicle terminating below in a roundish gland, concealed at first in the pouch-like rostellum at the front of the column.
In such cases the contact of an insect or other body with those processes is sufficient to liberate the pollen often with elastic force, even when the anther itself is not touched.
The object of these movements will be appreciated when it is remembered that, if the pollen-masses retained the original direction they had in the anther in which they were formed, they would, when transported by the insect to another flower, merely come in contact with the anther of that flower, where of course they would be of no use; but, owing to the divergences and flexions above alluded to, the pollen-masses come to be so placed that, when transplanted to another flower of the same species, they come in contact with the stigma and so effect the fertilization of that flower.
The Monandreae have been subdivided into twenty-eight tribes, the characters of which are based on the structure of the anther and pollinia, the nature of the inflorescence, whether terminal or lateral, the vernation of the leaf and the presence or absence of a joint between blade and sheath, and the nature of the stem.
Even in homogamous flowers cross-pollination is in a large proportion of cases the effective method, at any rate at first, owing to the relative position of anther and stigma or the fact that the plant is self-sterile.
Many plants produce, in addition to ordinary open flowers, so-called cleistogamous flowers, which remain permanently closed but which notwithstanding produce fruit; in these the corolla is inconspicuous or absent and the pollen grows from the anther on to the stigma of the same flower.
- Pollination I, Flower visited by a humblebee, showing the projection of the curved connective bearing the anther from the helmetshaped upper lip and the deposition of the pollen on the back of the humble-bee.
(For further details on the form and arrangement of the flower and its parts, see Flower.) Each stamen generally bears four pollen-sacs (microsporangia) which are associated to form the anther, and carried up on a stalk or filament.
The numerous male catkins are generally arranged in dense whorls around the bases of the young shoots; the anther-scales, surmounted by a crest-like appendage, shed their abundant pollen by longitudinal slits; the two ovules at the base of the inner side of each fertile cone-scale develop into a pair of winged seeds, which drop from the opening scales when mature - as in the allied genera.
A, Male flower and young cones; b, male catkin; c, d, outer and inner side of anther-scale.
25, f), supporting at its summit the anther (a), consisting of the pollen-sacs which contain the powdery pollen (p), the microspores, which is ultimately discharged therefrom.
Thus in Dicentra and Corydalis there are six stamens in two bundles; the central one of each bundle alone is perfect, the lateral ones have each only half an anther, and are really stipules formed from the staminal leaf.
25 f), and a broader portion, usually of two lobes, termed the anther (a), containing the powdery pollen (p), and supported upon the end of the filament.
That portion of the filament in contact with the anther-lobes is termed the connective.
Anther is absent the FIG.
Older flower with the stamens (S) anther is developed o n the c orolla dried up.er(X2) dth e hairs before the filament, and when the latter is not produced, the anther is sessile, as in the mistletoe.
- Portion of wall of anther of Wallflower (Cheiranthus).
- Quadrilocular or tetrathecal anther of the flowering Rush (Butomus umbellatus).
The anther entire (a) with its filament; section of anther (b) showing the four loculi.
The anther consists of lobes containing the minute powdery pollen grains, which, when mature, are discharged by a fissure or opening of some sort.
The walls of the cells are frequently absorbed, so that when the anther attains maturity the fibres are alone left, and these by their elasticity assist in discharging the pollen.
Sometimes, however, only two cavities remain in the anther, by union of the sacs in each lobe, in which case the anther is said to be bilocular or dithecal.
Occasionally there are numerous cavities in the anther, as in Viscum and Rafesia.
Below the anther the surface of the column in front is hollowed out into a greenish depression covered with viscid fluid - this is the two united stigmas.
- Two Stamens of Viola tricolor (Pansy), with their two anther lobes and the processp extending beyond them.
The perianth consists of five or six oblong greenish lobes, within which is found a tuft, consisting of a large number of stamens, each of which has a very short filament and an oblong two-lobed anther bursting longitudinally, and surmounted by an oblong lobe, which is the projecting end of the connective.
- Stamen, consisting of a filament (stalk) f and an anther a, containing the pollen p, which is discharged through slits in the two lobes of the anther.
The anther is developed before the filament, and is always sessile in the first instance, and sometimes continues so.
74), where there are two, and Poranthera, where there are four; whilst in the mistletoe the anther has numerous pores for the discharge of the pollen.