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    The affect of duration of light (or photoperiods) on the growth and development of plants, especially flowering and seed germination is called photoperiodism. For example, flowering of tobacco plants can be done in summer by decreasing the light hours.

    The chemical present in plants which responds to the photoperiodic stimulus is called phytochrome. Phytochrome is a blue-green pigment and present in small amount in plants.


    Some plants do not flower in warm seasons. Such plants remain vegetative during warm seasons. These plants flower only in winters when the temperature is low. Thus, such plants can be made to flower in summer season by providing them previous cold treatment. This process of stimulating flowering in plants by previous cold treatment is called vernalisation.

Test Your Understanding and Answer These Questions:

  1. What is Photoperiodism?

  2. What do you meant by vernalisation?

  3. What is phytochrome? Give an example.


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