$A$ : The generative cell comes to lie freely in the cytoplasm of the tube cell.
$R$ : Cellulosic wall around generative cell is dissolved.

How many meiotic divisions are necessary to produce $100$ pollen grains

After penetrating stigmatic and styler tissues, the pollen tube usually grow down towards the egg because

Assertion : If pollen mother cells has $42$ chromosomes, the pollen has only $21$ chromosomes.
Reason : Pollens are formed after meiosis in pollen mother cell.

Which of the following has proved helpful in preserving pollen as fossils?