Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion ? Also draw a labelled diagram of embryo sac to explain the phenomena.

$\rightarrow$  Pollen tube geminates on stigma of a flower and resulting pollentube passes through stigma and style and reaches upto egg appratus. Two gametes are released in embryo sac. Among them one male gamete fuses with egg cell and forms diploid zygote.

$\rightarrow$ This type of fusion is called fertilization or syngamy.

$\rightarrow$ The other male gamete fuses with secondary nucleus and it is called triploid primary endosperm nucleus. (PEN). It is called triploid fusion.

$\rightarrow$  Due to two types of fusion this event is known as double fertilization in angiosperms, after that zygote develops into embryo and PEN develops into endosperm that gives nourishment to developing embryo.