Pollen grains are well preserved as fossils because of the presence of . . . . . . .

What is the number of cells or nuclei present in the male gametophyte of Capsella?

Microsporogenesis is:

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:

The microspore is the first cell of the.......

Assertion $A$: Pollen grains are found in the form of fossils.
Reason $R$: Sporopollenin is seen in its outer layer.