As with all land plants, the life cycle of an angiosperm alternates between a diploid sporoffite generation, represented here by the flower of the mature sporoffite plant, and a haploid gametefite generation. Within the flower's male parts called the anthors, are millions of diploid spores called micro sporocytes. These micro sporocytes divide by meiosis to produce haploid microsports. Meanwhile, a similar process occurs within the flower's female parts, which consist of one or more carpals. In this example, the single carpal consists of a stigma, style, ovary and ovule. A single diploid mega sporocyte exists in the ovule and divides by meiosis to produce four haploid mega spores, only one of which survives. By producing two different types of spores, the microsports and megospores, angiosperms and all other seed plants are considered hetero spores. Each microspore undergoes a mitotic division and differentiation to produce a pollen grain. A pollen grain is the haploid male gametefite called a micro gametefite. The surviving megospore divides by meiosis to produce seven haploid cells, one large centrally located cell contains two nuclei, called poner nuclei. Another cell is the egg. The seven-celled structure makes up the female gametefite called the mega gametefite. The pollen grain pollinates the female parts of the flower by landing on the stigma. Here, the pollen grain germinates and a pollen tube grows down the style until it meets the female gametefite. Two sperm from the pollen grain travel through the pollen tube and enter the female gametefite. One fertilizes the egg, forming a diploid zygote. The other fertilizes two poner nuclei, forming a triploid cell. The fertilization of both the egg cell and the central cell is called double fertilization, a hallmark of the life cycle of angiosperms. The zygote, which begins the next sporefite generation, develops into the embryo, while the triploid cell develops into the nutritive endospirum of the seed. The seed germinates, and when the sporefite matures, the life cycle begins again.