For instance, one trait he studied was pod color. Some pea plants have green pods and others have yellow pods. Since pea plants are capable of self fertilization, Mendel was able to produce true-breeding plants. A true-breeding yellow-pod plant for example would only produce yellow-pod offspring. Mendel then began to experiment to find out what would happen if he cross-pollinated a true-breeding yellow pod plant with a true-breeding green pod plant. He referred to the two parental plants as the parental generation (P generation) and the resulting offspring were called the first filial or F1 generation.