During microsporogenesis, meiosis occurs in

1. endothecium

2. microspore mother cells

3. microspore tetrads

4. pollen grains

(b) As the anther develops, the microspore mother cells of the sporogenous tissue undergoes meiotic divisions to form microspore tetrads. The microspore tetrad after dehydration is separated into pollen grains. Endothecium is the layer present between epidermis and middle layer, it is formed by columnar cells.
Page 22, XII NCERT