What is the X in X-mas?
The tissue that surrounds and provides nourishment to the embryo in the seeds of many angiosperms. The cells of the endosperm arise from a process similar to that of fertilization. The pollen of angiosperms contains two sperm, one of which fertilizes the egg cell in the female gametophyte. The second unites with two other nuclei in the female gametophyte, producing cells that are triploid (having three sets of chromosomes) and that develop into the endosperm. In some species of angiosperms, the endosperm is absorbed by the embryo before germination, while in others it is consumed during germination. Embyros that lack an endosperm (such as peas and beans) have absorbed most of their food storage tissues before becoming dormant and develop large, fleshy cotyledons.
tissue that surrounds and nourishes the embryo in the angiosperm seed. The initiation of endosperm is a definitive characteristic of angiosperms and requires the fusion of at least one nucleus in the embryo sac with a sperm nucleus from the pollen grain. (In gymnosperms the nutritive material of the seed is present before fertilization.) In some seeds the endosperm has been completely absorbed at maturity (e.g., pea and bean); in others, some is present until germination (e.g., wheat, castor bean). In the coconut, the liquid endosperm contains important growth substances. Endosperm accounts for the economic importance of cereal grains and oilseeds.