How do Mendel’s experiments show that traits may be dominant or recessive?

Mendel showed that a trait can be dominant or recessive, by monohybrid cross.

As he used the tall plant of allele (T) and short plant of allele (t), when crossed they produced traits having TT, Tt and tt in the second generation. TT means tall and tt means small, but Tt meant to be tall not any intermediate height. So here T is dominant over t.