Gynecology Sexual anatomy

Stamen Wikipedia

Image:Amaryllis stamens aka.jpg|thumb|right|250 px|Stamens of the Amaryllis with prominent anthers carrying pollen
Image:Bee pollenating a rose.jpg|thumb|right|250 px|Insects, while collecting pollen, accidentally transfer it from one flower to another, bringing about pollination

The stamen is the male organ (anatomy)|organ of a flower. Each stamen generally has a stalk called the filament, and, on top of the filament, an anther.

The anther is usually composed of four pollen sacs, which are called sporangium|microsporangia. The development of the microsporangia and the contained haploid spores (called Pollen|pollen-grains) is closely comparable with that of the microsporangia in gymnosperms or heterosporous ferns. The pollen is set free by the opening (dehiscence) of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the Erica|heath family (Ericaceae), or by valves, as in the barberry family (Berberidaceae). It is then dropped, or carried by some external agent — wind, water or some member of the kingdom (biology)|animal kingdom — onto the receptive surface of the carpel of the same or another flower, which is thus pollination|pollinated.

Typical flowers have six stamens inside a perianth (the petals and sepals together), arranged in a whorl around the carpel (pistil). But in some species there are many more than six present in a flower (see, for example, the spider tree flower, below). Collectively, the stamens are called an androecium (from Greek language|Greek andros oikia: man's house). They are positioned just below the Carpel|gynoecium. The anthers are bilocular, i.e. they have two locules. Each locule contains a microsporangium. The tissue between the locules and the cells is called the connective.

In an immature, unopened flower bud, the filaments are still short. Their function is then to transport nutrients to the developing pollen. They start to lengthen once the bud opens. The anther can be attached to the filament in two ways:

• basifixed : attached at its base to the filament; this gives rise to a longitudinal dehiscence (opening along its length to release pollen)

• versatile : attached at its center to the filament; pollen is then released through pores (poricidal dehiscence).

Image:Penta anther.jpg|thumb|right|250 px|Scanning electron microscope image of Penta lanceolata anthers, with pollen grains on surface
Stamens can be connate (fused or joined in the same whorl):

• monadelphous : fused into a single, compound structure

• diadelphous : joined partially into two androecial structures

• synantherous : only the anthers are connate (such as in the Asteraceae)

Stamens can also be adnate (fused or joined from more than one whorl):

• epipetalous : adnate to the corolla

• didynamous : occurring in two pairs of different length

• tetradynamos : occurring as a set of six filaments with two shorter ones

• exserted : extending beyond the corolla

• included : not extending from the corolla.

Last Modified:   2005-12-19