Its two pollen-masses in o, The twisted ovary.
Owing, however, to the close proximity of stigma and anthers, very slight irregularity in the movements of the visiting insect will cause self-pollination, which may also occur by the dropping of pollen from the anthers of the larger stamens on to the stigma.
The anthers shed their pollen into this groove, either of themselves or when the pistil is shaken by the insertion of the bee's proboscis.
The conclusion at which he arrives is that the pollen is not in all flowering plants necessary for impregnation, for fertile seeds can be produced without its influence.
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.
POLLINATION, in botany, the transference of the pollen from the stamen to the receptive surface, or stigma, of the pistil of a flower.
Species of Cactaceae), or the style bends so that the stigma is brought within the range of the pollen (e.g.
The spores, as in the heterosporous Pteridophyta, are of two kindsmicrospores (pollen grains) borne in microsporangia (pollen sacs) on special leaves (sporophylls) known as stamens, and macrospores (embryo-sac) borne in macrosporangia (ovules) on sporophylls known as carpels.
The ANGIOSFERMS, which are much the larger class, derive their name from the fact that the carpel or carpels form a closed chamber, the ovary, in which the ovules are developedassociated with this is the development of a receptive or stigmatic surface on which the pollen grain is deposited.
2.Various Stages in the Nuclear Division of the Pollen i Mother-cells of Lilium.
Cross fertilization, or the impregnation of any given flower by pollen from another flower of the same species on the same or on another plant, has been proved to be of great - g advantage to the plant by securing a more FIG.
Havingattained its object the insect withdraws, taking the pollen-masses, and visits another flower.
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the base of the anther, when the disks adhere to the needle as they would do to the antenna of an insect, and may be withdrawn.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.
There is a close relation between the pollination of many yuccas and the life of a moth (Pronuba yuccasella); the flowers are open and scented at night when the female moth becomes active, first collecting a load of pollen and then depositing her eggs, generally in a different flower from that which has supplied the pollen.
Pollen may be transferred to the stigma of the same flower - self-pollination (or autogamy), or to the stigma of another flower on the same plant or another plant of the same species - crosspollination (or allogamy).
In Mirabilis Jalapa and others the filaments and style finally become intertwined, so that pollen is brought in contact with the stigma.
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.
A botanist notices that the bee flying with the pollen of a male flower to a pistil fertilizes the latter, and sees in this the purpose of the bee's existence.
The male gametophyte is represented by one or few cells and, except in a few primitive forms where the male cell still retains the motile character as in the Pteridophyta, is carried passively to the macrospore in a development of the pollen grain, the pollen tube.
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.
Bees carry the spores of Scierotinia as they do the pollen of the bilberries, and flies convey the conidia of ergot from grain to grain.
In such plants, the pollen grains are sometimes fihiform and not spherical in shape.
Cell, which is non-motile, is carried to the oosphere by means of a pollen tube.
They are present from the beginning of the development of the cell-wail, and arise from the spindle fibres, all of which may be continued as connecting threads (endosperm of Tamus communis), or part of them may be overlaid by cellulose lamellae (endosperm of Lilium Martagon), or they may be all overlaid as in pollen mother-cells and pollen grains of Helleborus foetidus.
Mottier, The Development of the Heterotype Chromosomes in Pollen Mother-cells, Ann.
Within the perianth, and springing from its sides, or apparently from the top of the ovary, are six stamens whose anthers contain pulverulent pollen-grains.
C, The one-celled ovary cut a, The anther, con transversely, having three taining pollen parietal placentas.
Moreover, the pollen, instead of consisting of separate cells or grains, consists of cells aggregated into "pollen-masses," the number varying in different genera, but very generally two, four, or eight, and in many of the genera provided at the base with a strap-shaped stalk or "caudicle" ending in a flattish gland or "viscid disk" like a boy's sucker.
4, r) in which the viscid disk of the pollen-masses is concealed till released in the manner presently to be mentioned.
G, Level of stigma; S, level of anthers; P, N, pollen grains and stigmatic papillae of long-styled form; p, n, ditto of short-styled form.
In many cases pollen has no effect on the stigma of the same flower, the plants are selfsterile, in other cases external pollen is more effective (pre-potent) than pollen from the same flower; but in a very large number of cases experiment has shown that there is little or no difference between the effects of external pollen and that from the same flower.
The former, which is a somewhat less favourable method than the latter, is effected by air-currents, insect agency, the actual contact between stigmas and anthers in neighbouring flowers, where, as in the family Compositae, flowers are closely crowded, or by the fall of the pollen from a (From Darwin's by permission.) FIG.
In 1703 Samuel Morland, in a paper read before the Royal Society, stated that the farina (pollen) is a congeries of seminal plants, one of which must be conveyed into every ovum or seed before it can become prolific. In this remarkable statement he seems to anticipate in part the discoveries afterwards made as to pollen tubes, and more particularly the peculiar views promulgated by Schleiden.
Amici discovered the existence of pollen tubes, and he was followed by A.
With respect to the production of hybrids, the genus is remarkable for its power of resisting the influence of foreign pollen, for the seedlings of any species, when crossed, generally resemble that which bears them.
His transcripts were brought to light by Father Pollen, S.
The insects visit the plant in large numbers, attracted by the foetid smell, and act as carriers of the pollen from one spathe to another.
See Lampel, Urkundenbuch des Chorherrenstifts Sankt Pollen (Wien, 1891-1901, 2 vols.).
Hybridization can also be readily controlled in the case of tobaccos, and in this connexion it is useful to note that, if pollen is desired of some variety growing at a distance, it will retain its vitality for several weeks if kept perfectly dry, and so can readily be sent by post from one place to another.
Some importance attaches to the form of the pollen grains; the two principal forms are ellipsoidal with longitudinal bands forming the Convolvulus-type, and a spherical form with a spiny surface known as the Ipomaea-type.