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The Anatomy of Flowers
By admin | June 28, 2006
I hope you will forgive me for getting a little technical today. I have received a number of emails asking about the function and anatomy of flowers. Evidently there are some truly passionate green fingered gardners out there that want to do more than just talk to their flowers and water the plants, people actually want to know what actually makes flowers grow.
So here is a brief guide to the anatomy of flowers:
The function of a flower is to mediate the union of male and female gametes. The process is termed pollination. Many flowers are dependent upon the wind to move pollen between flowers of the same species. Others rely on animals (especially insects) to accomplish this feat. The period of time during which this process can take place (the flower is fully expanded and functional) is called anthesis.
A flower is regarded as a modified stem (Eames, 1961) with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves. In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate). The stem is called a pedicel, the end of which is the torus or receptacle. The parts of a flower are arranged in whorls on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows
* calyx – the outer whorl of sepals; typically these are green, but are petal-like in some species
* corolla – the whorl of petals, which are usually thin, soft and colored to attract insects that help the process of pollination.
* androecium (from Greek andros oikia: man’s house) – one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes.
* gynoecium (from Greek gynaikos oikia: woman’s house) – one or more pistils.
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The female reproductive organ is the carpel: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called apocarpous). The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.
For example, the two subclasses of flowering plants may be distinguished by the number of floral organs in each whorl: dicotyledons typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and monocotyledons having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.
In the majority of species individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite. However, in some species of plants the flowers are imperfect or unisexual: having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either male or female the species is regarded as dioecious. However, where unisexual male and female flowers appear on the same plant, the species is considered monoecious.
Some flowers with both stamens and a pistil are capable of self-fertilization, which does increase the chance of producing seeds but limits genetic variation.
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The extreme case of self-fertilization occurs in flowers that always self-fertilize, such as the common dandelion. Conversely, many species of plants have ways of preventing self-fertilization. Unisexual male and female flowers on the same plant may not appear at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-sterile or self-incompatible.
Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis, the collection of flowers is termed an inflorescence. In this sense, care must be exercised in considering what a ‘‘flower’’ is. In botanical terminology, a single daisy or sunflower for example, is not a flower but a flower head an inflorescence comprised of numerous small flowers (sometimes called florets).
I hope that answers at least some of the question posed by some of our readers. Dot forget if you have any more requests for gardening tips or hose reel reviews, email them in.
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July 22nd, 2006 at 5:19 am
I find some information here.