Microspores Sentence Examples

The fertile leaves or sporophylls are generally aggregated on special shoots to form rioweN which may contain one or both kinds The microspores are set free from the sporangiurn and carried generally by wind or insect agency to the vicinity of the macrospore, which never leaves the ovule.

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 spores produced in each sporangium vary from very many to a single one in the case of some heterosporous forms. These latter bear spores of two kinds, microspores and megaspores, in separate sporangia.

Some Calamites were heterosporous, sporangia with microspores and megaspores being found in the same cone.

The sporogenous tissue, which is referable to several archesporial cells, is surrounded by a tapetum, mostly derived from the sporogenous group. In the microsporangium all the mother-cells undergo the tetrad division, giving rise to the numerous microspores.

On germination the microspores give rise to a reduced prothallus, consisting of the small cell first cut off and a wall of cells enclosing two to four central ones; "from these latter the biciliate spermatozoids originate.

The microspores on germination produce a small, greatly reduced male prothallus bearing one or two antheridia which give rise to a number of spirally coiled, multiciliate spermatozoids.

The microspores are united by means of hardened protoplasm into one or more masses, while the solitary megaspores have a more or less complicated episporium.

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.

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

The spores of this genus are curiously winged, and intermediate in size between the microspores and megaspores of Lepidostrobus; the question of homospory or heterospory is not yet decided.

The microspores are tetrahedral.

Nathorst has recently described a new type of lycopodiaceous cone, Lycostrobus Scotti, from Rhaetic rocks of Scania, from which he obtained both megaspores and microspores.

The synangia consist of a stout wall composed of thick-walled cells, succeeded by a layer of more delicate and smaller elements; and internal to the wall occur two rows of sporangial loculi containing microspores.

As with few exceptions the stamen represents a leaf which has been specially developed to bear the pollen or microspores, it is spoken of in comparative morphology as a microsporophyll; similarly the carpels which make up the pistil are the megasporophylls (see Angiosperms).