In anther culture,the androgenic haploid plants are obtained from

How many microspores are formed from a single microspore mother cell?

$A$ - Only some cells of the sporogenous tissue are capable of giving rise to microspore tetrad.
$R$ - The microspores are arranged in a cluster of four cells - the microspore tetrad.

Identify $A$ and $B$ in the diagram given below:

When a pollen grain is shed at the $3$-celled stage,name the cells it contains.

The development of the male gametophyte takes place in ........