Pollen-sacs sentence example

  • The male flower of Cycas conforms to the type of structure characteristic of the cycads, and consists of a long cone of numerous sporophylls bearing many oval pollen-sacs on their lower faces.
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  • The sporangia (pollen-sacs), which occur on the under-side of the stamens, are often arranged in more or less definite groups or sori, interspersed with hairs (paraphyses); dehiscence takes place along a line marked out by the occurrence of smaller and thinner-walled cells bounded by larger and thickerwalled elements, which form a fairly prominent cap-like " annulus " near the apex of the sporangium, not unlike the annulus characteristic of the Schizaeaceae among ferns.
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  • The frequent occurrence of more than two pollen-sacs and the equally common occurrence of additional ovules have been regarded by some authors as evidence in favour of the view that ancestral types normally possessed a greater number of these organs than are usually found in the recent species.
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  • A typical male flower consists of a central axis bearing numerous spirally-arranged sporophylls (stamens), each of which consists of a slender stalk (filament) terminating distally in a more or less prominent knob or triangular scale, and bearing two or more pollen-sacs (microsporangia) on its lower surface.
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  • The stamens of Araucaria and Agathis are peculiar in bearing several long and narrow free pollen-sacs; these may be compared with the sporangiophores of the horsetails (Equisetum); in Taxus (yew) the filament is attached to the centre of a large circular distal expansion, which bears several pollen-sacs on its under surface.
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  • The male flowers are developed at the ends of short lateral branches, are rounded or oblong in form, and consist of several antheriferous scales in two or three rows, each scale bearing three or six almost spherical pollen-sacs on its under side.
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  • 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.
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  • Upon these projections the rudiments of the pollen-sacs are then seen, usually four in number, two on each lobe.
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  • 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.
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  • Then the walls of the mother-cells are absorbed, and the pollengrains float freely in the fluid of the pollen-sacs, which gradually disappears, and the mature grains form a powdery mass within the anther.
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  • The fructifications by themselves are not necessarily decisive, for in certain cases the supposed sporangia of Marattiaceous Ferns have turned out to be in reality the microsporangia or pollen-sacs of seed-bearing plants (Pteridosperms).
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  • Some of the pollen-sacs had dehisced, while others still retained their pollen.
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  • The occasional occurrence of three or even four pollen-sacs on the stamens of the recent species affords a still closer agreement between the extinct and living types.
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