Pollen-grains Sentence Examples

In such plants, the pollen grains are sometimes fihiform and not spherical in shape.

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.

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.

Najas where the pollen grains are rather heavier than water, and sinking down are caught by the stigmas of the extremely simple female flowers.

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).

The two forms have long and short styles repectively, the stamens occupying corresponding positions half-way down or at the mouth of the corolla-tube; the long-styled flowers have smaller pollen-grains, which correspond with smaller stigmatic papillae on the short styles.

The sporangial wall, consisting of several layers of cells, encloses a cavity containing numerous oval spores (pollen-grains).

The pollen-grains when mature consist of three cells, two small and one large cell; the latter grows into the pollen-tube, as in the Coniferales, and from one of the small cells two large ciliated spermatozoids are eventually produced.

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.

In Araucaria and Saxegothaea the nucellus itself projects beyond the open micropyle and receives the pollen-grains direct.

The fungus-spores, from some diseased plant, alight on the stigma of the flower, and germinate there along with the pollen-grains.

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 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.

These cells are the pollen-grains.

Occasionally the membrane of the mother-cell is not completely absorbed, and traces of it are detected in a viscid matter surrounding the pollen-grains, as in Onagraceae.

Pollen-grains vary from a o 0 - to o-y of an inch or less in diameter.

Pollen-grains are also spherical; cylindrical and curved, as in Tradescantia virginica; C From Vines' Students' Text-Book of Botany, by permission of Swan Sonnenschein & Co.

When the pollen-grains are ripe, the anther dehisces and the pollen is shed.

Nucellus of an ovule; p.c, pollen-chamber; s, canal leading to p.c; p, pollen-grains in p.c; p', do.

Upper part of seed, in longitudinal section; i, integument; mi, micropyle; n, remains of nucellus; p.c, pollen-chamber (containing pollen-grains), with its canal extending up to the micropyle; pr, part of prothallus; ar, archegonia.

In the isolated seeds of Cordaitales and Pteridosperms, pollen-grains are often found within the pollen-chamber, and the pluricellular structure of these pollen-grains has been repeatedly demonstrated.

The male sporophylls are similar in form to the vegetative leaves, but smaller; sunk in their parenchyma are numerous tubular loculi, containing large pollen-grains, which are pluricellular like those of Cordaites; the female fructification had not yet been identified with certainty.

Spring squill has blue anthers, these are the parts on the ends of the stamens which carry the pollen grains.

The pollen grains grow down from the stigma to fertilize the ovules in the ovary at the base of the style.

Under the microscope, an anther can be seen to have many spherical to ellipsoidal pollen grains on its surface.

All pollen grains develop initially in groups of four called tetrads.

Gazette, xlvi., 1908, regards this tissue as belonging to the nucellus.) At the time of pollination the long tubular integument secretes a drop of fluid at its apex, which holds the pollen-grains, brought by the wind, or possibly to some extent by insect agency, and by evaporation these are drawn on to the top of the nucellus, where partial disorganization of the cells has given rise to an irregular pollen-chamber (fig.