To obtain the F1 generation Mendel pollinated a pure-breeding tall plant with a pure breeding dwarf plant. But forgetting the F2 generation, he simply self-pollinated the tall F1 plants. Why?
To prevent the masking of the effect of inheritance to F2 generation by character set, Mendel self-pollinated the tall F1 plants. This is because all plants of the F1 generation turned out to be tall and he could not understand the fate of the recessive character.