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megasporangium

megasporangium

megasporangium Sentence Examples

  • In the megasporangium, on the other hand, the four megaspores, which arise from a single mother-cell, are nourished at the expense of the other sporogenous cells and of the tapetum.

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  • In some of the heterosporous forms (Lepidocarpon, Miadesmia) the sporangia were sometimes surrounded by an integument; and since only a single megaspore attained maturity, the structure of the megasporangium suggests a comparison with an ovule.

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  • The latter are more numerous in the microsporangium than in the megasporangium.

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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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  • The megaspores, of which there are many in the megasporangium, have a diameter about three times that of the microspores.

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  • The seed, which need not be described in further detail, was a highly organized structure, showing little trace of the cryptogamic megasporangium from which we must suppose it to have been derived.

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  • In the megasporangium, on the other hand, the four megaspores, which arise from a single mother-cell, are nourished at the expense of the other sporogenous cells and of the tapetum.

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  • In some of the heterosporous forms (Lepidocarpon, Miadesmia) the sporangia were sometimes surrounded by an integument; and since only a single megaspore attained maturity, the structure of the megasporangium suggests a comparison with an ovule.

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  • The latter are more numerous in the microsporangium than in the megasporangium.

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  • The single large megaspore contained in each megasporangium produces a small prothallus, which bears one or a few archegonia; these are exposed on the surface of the prothallus at the summit of the germinated megaspore (fig.

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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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  • The megaspores, of which there are many in the megasporangium, have a diameter about three times that of the microspores.

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  • In this fructification the organization is at first altogether that of a Lepidostrobus; in each megasporangium, however, only a single megaspore came to maturity, occupying almost the whole of the sporangial cavity (see fig.

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  • Each sporophyll bears a megasporangium, attached to its upper surface at the proximal end, containing a single large megaspore (fig.

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  • The megasporangium is enclosed in an a A"° cu integument, which completely envelopes it, leaving only a narrow micropyle at the distal end (fig.

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  • The seed, which need not be described in further detail, was a highly organized structure, showing little trace of the cryptogamic megasporangium from which we must suppose it to have been derived.

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