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Newport and others; namely the fact that the fertilizing filament reaches the interior of the ovum in various animals; a striking parallel to the action of the pollen-tube in the vegetable. But beyond the mechanical facts all is mystery in the movements of organization, as profound as in the fall of a stone or the formation of a crystal.
Fertilization. At the period of fertilization the embryo-sac lies in close proximity to the opening of the micropyle, into which the pollen-tube has penetrated, the separating cell-wall becomes absorbed, and the male or sperm-cells are ejected into the embryo-sac.
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.
Newport and others; namely the fact that the fertilizing filament reaches the interior of the ovum in various animals; a striking parallel to the action of the pollen-tube in the vegetable. But beyond the mechanical facts all is mystery in the movements of organization, as profound as in the fall of a stone or the formation of a crystal.
The anther is attached at the back of its base or middle to the top of the filament in the suture separating the two large cells. These anther-cells split along the outer margins, releasing the pollen-grains. It is down these style-branches that the pollen-tube passes on its way to the ovules or embryo seeds. The top of the style is expanded into a cupped stigma on which are many glutinous points.
The nucleus of the tube-cell has meanwhile passed into the tube, as does also the generative nucleus which divides to form two male- or sperm-cells. The male-cells are carried to their destination in the tip of the pollen-tube. Pistil and embryo-sac. The ovary contains one or more ovules borne on a placenta, which is generally some part of the ovary-wall.
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. Such a method of entrance is styled chalazogamic, in contrast to the porogamic or ordinary method of approach by means of the micropyle. Embryology.
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