The reproductive part of the plant, flower, has the male and female sex organs. Such flowers having both the sex organs are called bisexual or monoecious flower. To avoid self-pollination, in such flowers the male and female parts do not mature at the same time. In plants like arum lilies, apple the female part mature before the male part. Such condition is called protogyny. Ivy, rosebay show protandry where the anther matures before pistil. Such situation avoids self-pollination and promotes self pollination leading to cross fertilization. Cross-fertilisation is a process in which gametes derived from different individuals are united to form the zygote. This process mixes the genetic materials and also introduces variation.