C, The one-celled ovary cut a, The anther, con transversely, having three taining pollen parietal placentas.
Floral diagram of typical orchid flower; 1, labellum; a, anther; s, rudiments of barren stamens (staminodes).
They are attracted to the flower by its colour or its perfume; they seek, collect or feed on its honey, and while so doing they remove the pollen from the anther and convey it to another flower, there to germinate on the stigma when its tubes travel down the style to the ovary where their contents ultimately fuse with the "oosphere" or immature egg, which becomes in consequence fertilized, and forms a seed which afterwards develops into a new plant (see article Angiosperms).
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.
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.
The movements of the pollen-masses may readily be seen with the naked eye by thrusting the point of a needle into the base of the anther, when the disks adhere to the needle as they would do to the antenna of an insect, and may be withdrawn.
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.
The five anthers are remarkable for the coloured processes which extend beyond the anther cells and form a sort of cone around the style (fig.
- Two Stamens of Viola tricolor (Pansy), with their two anther lobes and the processp extending beyond them.
A, anther; s, pistil; st, style; v, stigmatic surface.
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.
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.
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.
Water plants, where flowers are un- a, anther; s, pistil; able to reach the surface (e.g.
9, 2) the style elongates and the forked stigma occupies the same position as the anther in fig.
- 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.
- I, anther; 2, pollen grain of Hollyhock (Althaea rosea) enlarged.
(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 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.
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.