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Cultivated cotton plants grow to about 1 to 2 metres
tall. The plant produces white flowers from a bud. When the bud
has flowered, it turns pink and the petals fall off. Seeds
that are then formed in a small green pod called the cotton
boll. Huge numbers of seed hairs form around each seed and these white
fibres become packed around the seed inside the boll. When
the boll is mature, it bursts open, showing the soft cotton fibres,
which exist to help the cotton seeds to be distributed.
This is the cotton fibre that we harvest.
Cotton fibres are about 2 - 4 centimetres in length. They
are made up of about 87 - 90 per cent cellulose.
This is a tough carbohydrate molecule that makes up the cell wall
of all plants. The fibres also contain 5 - 8 per cent water, and
about 5 per cent other substances.
The length of the cotton fibre determines the quality,
and therefore the price, of the cotton produced. The longest fibres
are woven into the highest quality cotton fabric.
A major insect pest of the cotton plant is the
cotton boll weevil. The US company Monsanto has developed a variety
of cotton with built-in resistance to the boll weevil, and other
scientists are researching the use of viruses and venoms to kill
cotton pests.
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