Mendel selected Pisum sativum experimental material. He took two contrasting traits (allelomorphic traits). Contrasting traits are the two alternative forms of a character. Tall and dwarf are the contrasting traits of a character length of the stem in Pisum sativum. A pure line is the one that produces the identical progeny on self-pollination or self-fertilization. On self-pollination, a pure plant produces all tall plants and a dwarf plant produces only dwarf plants.