Pollen is transferred from stamen of one plant to the stigma of a different plant. Can be either by insect or wind. Once on the stigma a pollen grain a pollen tube which enters the ovule containing an egg cell. The nucleus inside the pollen grain joins with the nucleus inside the egg cell to form a zygote. This is called fertilization. The zygote grows into an embryo and the ovule becomes a seed, containing the embryo and a food store