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Sexual Reproduction

Since the castor bean is an angiosperm it relies on seeds to reproduce, unlike non-flowering plants that instead use spores to reproduce.  The flower of the plant is simply a bunch of modified leaves.

The outermost layer of these leaves being called the perianth is comprised of sepals.  A sepal is a green part of the flower that lies under the petals and is used to protect the flower.  The castor bean plant does not have petals but if it did the petals purpose would be to attract pollinators.  Want to learn about another plant that has petals?  Click here to learn about the common blue violet!  Inside of the perianth is where the reproductive organs of the flower lie.  The reproductive organs include the stamen and the carpels.  The stamens produce diploid pollen which ultimately produces the male gametes via meiosis.  The carpels contain an ovary with diploid ovules which produce the female gametes via meiosis.  Since both female and male gametes are produced via meiosis they are haploid.  After meiosis they undergo mitosis.  Mitosis is where the original cells reproduce genetically identical cells to increase their size.  The transfer of pollen to the stigma, the receptive surface of the carpel, is called pollination.  After pollination nuclei from the pollen fuses with nuclei from the ovule’s embryonic sac to form the seed.  This process can be seen more clearly in the picture directly below.

The Seed: some unique properties

The germination of the castor bean is extremely similar to the garden bean except that the castor bean stores food in the endosperm.  As the stem begins to develop it straightens out and comes out of the ground bringing the seed coat, cotyledons and plummule out of the ground with it.  The stored food is then digested and absorbed by the cotyledons.  After absorption the nutrients are transported to the growing parts of the plant.  The cotyledon becomes green when exposed to light but it doesn’t play an important role in photosynthesis.  In comparison the squash’s cotyledons become very important in photosynthesis. 


Cross-fertilization is essential to long term survival of any species because it ensures a varied population.  Flowering plants have developed many different techniques to ensure that this happens.  The first is the separation of the sexual organs.  Being that the castor bean plant has both male and female flowers on the same plant, it is monoecious (meaning one house).  With there being two different sexes of flower this allows the genetic material of both flowers to be placed into the seed.  Another technique used is the specialization of pollination mechanisms.  Many plants will specialize their pollination mechanisms adapting them to a specific insect, bird or bat.  This specialization of the flower structure ensures cross-pollination.

Want to learn more about reproduction in angiosperms?  Click here and explore Professor C.M. Sean Carrington's web page!

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