The law of segregation of characters is also called the law of purity of gametes because

If a plant heterozygous for tallness is selfed, the $F_2$ generation has both tall and dwarf plants. This proves the principle of

Cross between the pure tall plant from $F_1$ and dwarf plant will give

Percentage of recessive phenotype in a cross between $pp$ and $Pp$, when $P$ is dominant, $p$ recessive

The crossing of a homozygous tall plant with a dwarf in $F2$ would yield plants in the ratio of