Mendel conducted breeding experiments on pea plants :
He selected pure breed tall and dwarf plants. $\mathrm{He}$ cross pollinated these plants. In the ${\mathrm{F}}_1$ generation obtained only tall plants, tallness is the dominant trait.
Then, he produced ${\mathit{F}}_2$ generation by selfing of hybrids of ${\mathit{F}}_1$ generation. He found that $3∕4$ th of the plants were tall and $1/4$ th were dwarf. The trait which remains hidden in ${\mathit{F}}_1$ generation plants is the recessive trait.