From 1856 to 1863, he conducted pea hybridization experiments for 8 years. Pea is usually self-fertilized, but Mendel artificially crossed a tall variety with a short variety and obtained seeds that only produced tall plants. When this seed selfs, it produces 3: 1 tall and short plants. Dwarf plants produced in this way always produce the same offspring, but only one of the three tall plants does, and the other two still produce tall and short plants in a ratio of three to one. Mendel explained his experimental results as follows: every plant has two factors that determine height traits, and each parent is given a factor. The high factor is dominant and the low factor is recessive, so the plants of the first generation after hybridization are all tall. When this generation selfs, the arrangement of these factors in the offspring can be two high factors together, two short factors together, one high and one short, one short and one high. The first two combinations will produce the same offspring, each combination will produce all tall or short plants, and the latter two combinations will produce tall or short plants in a ratio of three to one.