In angiosperms,the male gametes are produced by the division of the ..........

One pollen mother cell may produce four germinating pollen grains,each with two male nuclei and one tube nucleus. How many meiotic divisions are necessary to bring this about?

Which is an incorrect statement?
$I$. Each cell of sporogenous tissue in anther is capable of giving rise to a microspore tetrad.
$II$. The pollen grain represents the male gametophyte.
$III$. Pollen grains are usually triangular and $10-15 \mu m$ in diameter.
$IV$. Sporopollenin is one of the most resistant organic materials,which can be destroyed only by strong acids and alkalis.

Among the following statements related to pollens, choose the correct one.
Statement $I$: In $40\%$ of angiosperms, pollen grains are shed at the $3$-celled stage.
Statement $II$: Intine is made of cellulose and pectin, and it is discontinuous with germ pores.

Microsporogenesis is:

Describe the location and function of the $Endothecium$ and $Tapetum$.