Pea plants were the plant of choice for geneticist Gregor Mendel (1822-1884) when he was experimenting with hybridisation. Since the flowers have both male and female sex organs, peas can reproduce by self-pollination or cross-pollination. Mendel was able to manipulate the genetic make-up of a pea plant's offspring by manually introducing the pollen of one type of pea plant to the female sex organs of another. Self-pollination, on the other hand, requires only one plant.
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Flowers come in two different types. Blossoms that have only the male or female sex organs are called imperfect flowers. Peas have perfect flowers, which have organs of both sexes. The male sex organs are called stamens. These are made up of the filaments, long strands that grow from the base of the flower to the tops of the flower petals. At the tips of the filaments are the anthers, sticky pads that hold the pollen. The pistil is the female organ and grows in the centre of the flower, from the base to the petal tops. The ovary, which will hold the future seeds, is on the bottom and the stigma, the sticky surface that will catch the pollen is on the top. A narrow tube called the style runs through the centre of the pistil from the stigma to the ovary. The style carries the pollen into the ovary for fertilisation.
Common garden pea flowers (Pisium sativum) are either purple or white, have five petals and an irregular shape. The largest petal is at the top, flanked by two smaller petals on the side, called wings and two on the bottom, also smaller, that grow together forming a shape like a canoe. A pea plant with white flowers that self-pollinates will have offspring with white flowers. The same is true for the pea plants with purple flowers. Other traits that remain true due to self-pollination include wrinkled or smooth seeds and if the pod or seed is yellow or green.
Pea flowers tend to self-pollinate because the pollination usually occurs before the flower is fully open. If the flower opens early and the stigma is ready but the pollen isn't, then it is possible that cross-pollination, usually by insects, can occur. Farmers tend to keep different types of peas separated by at least 50 feet to keep them from pollinating each other. Cross-pollination rarely occurs in cooler climates, such as in the Rocky Mountains.
Self-pollinating plants do not need the help of insects or animals to transfer pollen from one flower to another, so they do not have to use excess energy and nutrients to create large showy blossoms. Pea plants, like other self-pollinating plants, can grow in isolated areas and still be assured of reproduction. Genetically, the generations of plants produced by the parent pea plant will be more uniform. This is known as true-breeding. This is good for the plants because they will continue to carry the traits that let them survive in similar conditions. Self-pollination of pea plants is also good for farmers growing the plants as a cash crop. The pods and seeds are fairly uniform in size, making them more marketable. The pods all tend to ripen at the same time, making harvesting easier.
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