How many microsporangia does a typical angiosperm anther contain?

The process of microsporogenesis is known as:

Which statement is correct regarding pollen grains?

The microspore tetrad of an angiosperm,at the time of formation,is surrounded by a callose wall. The breakdown of this wall is brought about by the enzyme callase,which is synthesized by the:

When mature anthers of $Datura$ $innoxia$ are cultured in a culture medium supplemented with phytohormones named kinetin,coconut milk,and plum juice,several embryos can be obtained floating inside the microsporangia. These embryos can develop into plants that are:

In over $60\%$ of angiosperms,pollen grains are shed at which of the following stages?