After penetrating stigmatic and styler tissues, the pollen tube usually grow down towards the egg because

$A$ : Growth of male gametophyte is completed over the female reproductive organ.
$R$ : $2-$celled stage of partial male gametophyte is developed in-situ.

In an young anther the four rows of cells which later produce pollen are called

Assertion : Pollen mother cells $(PMCs)$ are the first male gametophytic cells.
Reason : Each $PMC$ gives rise to two pollens.