Friday, July 6, 2007

Orchids... continued ...

Anatomy and function of the angiosperm flower. Following are the main features of angiospermflowers. Not all features are found in all flowers, as there has been considerable evolution and modification of this basic pattern.
a complete flowers consists of: Sepals + Petals + Stamen + Carpel

Sepals . These are the outermost tissues of the flower; they are what you see of a flower when in the bud stage, before it opens. Usually the sepals are green in color and photosynthetic. Collectively the sepals (there may be 3 or more) are termed the calyx.

Petals. These are the usually colored tissues that make flowers attractive to us and other animals.The petals may be equipped with nectar glands near their base, an attraction and reward for pollinators. Collectively the petals are termed the corolla.

Stamen. The stamens can be regarded as the male part of the flower. A stamen consists of 2 parts ... filament and anther. The anther is where pollen is made. Pollen grains are tiny male gametophytes in the life cycle of angiosperms. Pollen grains therefore are important because they are the source of sperm in the angiosperm life cycle.

Carpel. The carpel is the female part of a flower (not all flowers have male and female parts, butmost do). A carpel consists of 3 parts: stigma, style and ovary. The stigma is a sticky surface where pollen grains land and attach. The pollen grain bursts open and sends a sperm cell down through the style into the ovary. Within the ovary are the eggs = ovules. When fertilized, an egg becomes the seed. The ovary walls, which surround the eggs/seeds becomes the fruit of the flower. Thus an apple is really the expanded and enlarged ovary of the apple flower.

reference: ... Plant and Animal Diversity ... ...

One interesting feature that distinguishes the orchid from other flower groups is the union of the male parts and female parts of the flower. Orchids have three pistils and three stamens and they are fused into a column (gynostemium). Most orchids have only one fertile stamen, although slipper orchids such as Phragmipedium, Paphiopedilum, Selenipedium, and Cypripedium have two fertile stamens. The pollen grains of the fertile stamens are clustered into packets called massulae or more sticky units called pollinia. Orchid groups are ordinarily defined by the number of pollinia present.

Orchids have interesting pollination techniques. Although some Orchids are self-pollinated, the remainder are pollinated by bees, wasps, gnats, flies, moths, butterflies, ants, and birds. These animals are attracted in different ways often to a specific species. Some bees are attracted to certain groups of Orchids because of their scent. The bees work over the flowers collecting scented droplets, thus pollinating the flowers. Some flowers resembling female insects by appearance and scent. The males are tricked and attempt to mate with or steal away the "female insect" and thus flies away with pollinia and/or has deposited pollinia onto the stigma from another flower. Some flowers have sensitive labellums which closes against the column as soon as it's touched. The trapped insect must squeeze through a slim tunnel between the column and tip of the labellum to escape, consequently attaching pollinia to its body. Some blossoms are brightly colored to attract butterflies, while some are dull, but fragrant at night, in order to attract moths. Some are brightly colored and supplied with sweet nectar to attract birds.

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