question_answer 65)

  The generative cell of a two celled pollen divides in the pollen tube, but not in a three celled pollen. Give reasons.

Answer:

                  In over 60 % of angiosperms, pollen grains are shed at this 2-celled stage tube cell orvegetative cell generative cell. In the remaining species, the generative celldividesmitotically to give rise to the two male gametes before pollen grains are shed tubecell orvegetative cell two male gamete 3-celled stage. In 3 celled stage, the pollen grains further germinate on the stigma to produce pollen tubethrough one of the germ pores. The contents of the pollen grains move into the tube pollentube grows through the .tissues of the stigma and style and reaches to ovary. Inplants, when pollen grainare shed at 2 celled stage the generative cell divides and formtwo male gametes during the growth of the pollen tube in the stigma.