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

Mendel used a number of contrasting visible characters of garden peas – round/wrinkled seeds, tall/short plants, white/violet flowers and so on. When he crossed plants with contrasting characters, there were no halfway characteristics in the first generation. For example, if a tall plant was crossed with a short plant, all plants were either tall or short and no plant was found with medium height. In F₂ generation cross between two tall plants gave short plant as well. This proved that there are two contrasting characters out of which one is dominant which masks the effect of other which is recessive.