Endosperm is generally a plant tissue within the seeds of flowering plants. It is also termed as a nutritive tissue as it surrounds the developing embryo, providing enough nutrients (carbohydrates, oils and proteins) for it to grow and eventually grow into a plant.
Endosperm is one of the primary sources of human nutrition as it provide enough carbohydrates available for consumption.
Endosperm is produced when two sperm nuclei in the pollen grain reaches the female gametophyte in the embryo sac. One of the sperm nuclei fertilizes the egg and eventually forms into a zygote. The other sperm fuses with the polar nuclei in the embryo sac producing the primary endosperm cell.
The endosperm makes the main source of food for the embryo. In gymnosperms the endosperm is haploid and forms a continuation of the female gametophyte. On the other hand, in angiosperms it is formed mastly as the result of a fusion of the two polar nuclei and one of the male gametes. Since all the three nuclei taking part in the fusion are haploid, the endosperm becomes triploid. In normal cases the endosperm is triploid but haploid, tetraploid and polyploid endosperms are also known. Generally the endosperm nucleus divides after the division of the oospore, but in several cases the endosperm is formed to a great extent even before the first division of the oospore.