In botany, seed is an undeveloped plant embryo and food reserve enclosed in a protective outer covering. More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote, forming a seed coat around the ovule, and grows within the mother plant to a certain size before growth is halted. The formation of the seed is a part of the process of reproduction in seed plants (spermatophytes). Other plants such as ferns, mosses and liverworts, do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates. In the flowering plants, the ovary ripens into a fruit which contains the seed and serves to disseminate it. Many structures commonly referred to as "seeds" are actually dry fruits. Sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits (such as the peach) have a hardened fruit layer (the endocarp) fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut. History The first land plants evolved around 468 million years ago, and reproduced using spores. The oldest seed bearing plants were gymnosperms, which had no ovaries to contain the seeds, arising sometime during the late Devonian period (416 million to 358 million years ago) From these early gymnosperms, seed ferns evolved during the Carboniferous period (359 to 299 million years ago); they had ovules that were borne in a cupule, which were groups of enclosing branches likely used to protect the developing seed. Published literature about seed storage, viability and its hygrometric dependence began in the early 19th century, influential works being: 1832 seed storage guide in Augustin Pyramus de Candolle's Conservation des Graines, part of his 3-volume Physiologie végétale, ou Exposition des forces et des fonctions vitales des végétaux (1832, v. 2, pp. 618-626, Paris); (translated title, "Plant physiology, or Exposition of the vital forces and functions of plants") 1846 viability studies by Augustin de