What acts as a mediator in the pollen-pistil interaction?

Pollen grains can be stored for years in ........

Identify the correct sequence of events of pollen-pistil interaction given below.
$(a)$ Pollen tube grows through the stigma,style and reaches the ovule.
$(b)$ Pollen grain lands on the stigma.
$(c)$ Pollen germinates to form pollen tube.
$(d)$ Pollen tube carrying $2$ male gametes enters the ovule.
Choose the correct option.

The pollen tube enters the embryo sac through:

Which solution can be used to induce the germination of pollen grains and the formation of a pollen tube in plants?

What type of growth is observed in the pollen tube?