Callose wall surrounds the sporocytes during the meiotic stage. It provides an isolation barrier sealing off one meiotic cell (megaspore mother cell) from another.
Related Theory
Tetrad is a group of four haploid and immature pollen grains in tetrahedral fashion produced by meiotic microsporogenesis. The tetrads are of five types namely tetrahedral (most common), isobilateral, $T$ shaped, decussate and linera. In dicots, the most common type of pollen tetrad is tetrahedral.