Stamen
The stamen is the male 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
microsporangia. The development of the
microsporangia and the contained haploid
spores is closely comparable with that of the microsporangia in
gymnosperms or heterosporous
ferns. The pollen is set free by the opening of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the
heath family , or by valves, as in the
barberry family .
Encyclopedia
The
stamen is the male 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
microsporangia. The development of the
microsporangia and the contained haploid
spores is closely comparable with that of the microsporangia in
gymnosperms or heterosporous
ferns. The pollen is set free by the opening of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the
heath family , or by valves, as in the
barberry family . It is then dropped, or carried by some external agent — wind, water or some member of the animal kingdom — onto the receptive surface of the
carpel of the same or another flower, which is thus
pollinated.
Typical flowers have six stamens inside a
perianth , arranged in a whorl around the carpel . But in some species there are many more than six present in a flower . Collectively, the stamens are called an
androecium . They are positioned just below the
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
- versatile : attached at its center to the filament; pollen is then released through pores .
Stamens can be
connate :
- monadelphous : fused into a single, compound structure
- diadelphous : joined partially into two androecial structures
- synantherous : only the anthers are connate
Stamens can also be
adnate :
- 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.
Plant sexuality
- Main article: Plant sexuality
In the typical flower each flower has both a
pistil and
stamens. Bisexual plants are named
hermaphrodites or perfect flowers.
In some species, however, the flowers are unisexual with only either male or female parts . A flower with only male reproductive parts is called
androecious. A flower with only female reproductive parts is called
gynoecious.
A flower having only functional stamens is called a
staminate flower.
An abortive or rudimentary stamen is called a
staminodium, such as in
Scrophularia nodosa of the family Scrophulariaceae [i] comprises about 200 species of herbaceous [i] ...
.
The pistil and the stamens of
orchids are fused into a
column. The top part of the column is formed by the anther. This is covered by an
anther cap.
References
