🍓 Pollination and double-fertilisation

Pollination is the journey of the pollen grain from the anther down the style of the ovary to reach the ovule. But first, how are pollen grains and embryo sacs developed?

 

 

Similarly to mammalian gametes, precursor pollen cells undergo meiosis to form 4 offspring cells that become the mature pollen grains. These have specific structure that take part in different aspects of fertilisation, namely the generative nucleus which gives rise to the male gametes proper and contributes to the final zygote once in the ovule, as well as the tube nucleus whose function is to transport the pollen to the embryo sac in the ovule.

 

 

The development of the embryo sac involves many divisions. The first is meiosis which results in one inner cell that develops further and 3 other cells that degenerate (remember polar cells in ovum development in mammals? same thing!). This is now the embryo sac. and it undergoes mitosis three times. The final mitosis of a 4-nucleus cell results in the embryo sac having 8…