Editing Seed (section)

=== {{anchor|Seed coat}}Seed coat ===
{{Redirect|Seed coat|artificial coat|Seed coating}}
The maturing ovule undergoes marked changes in the integuments, generally a reduction and disorganization but occasionally a thickening. The seed coat forms from the two integuments or outer layers of cells of the ovule, which derive from tissue from the mother plant, the inner integument forms the '''tegmen''' and the outer forms the '''testa'''. (The seed coats of some monocotyledon plants, such as the grasses, are not distinct structures, but are fused with the fruit wall to form a [[Fruit anatomy#Anatomy of simple fruits|pericarp]].) The testae of both monocots and dicots are often marked with patterns and textured markings, or have wings or tufts of hair. When the seed coat forms from only one layer, it is also called the testa, though not all such testae are [[Homology (biology)|homologous]] from one species to the next. The funiculus abscisses (detaches at fixed point&nbsp;– abscission zone), the scar forming an oval depression, the '''[[Hilum (biology)|hilum]]'''. Anatropous ovules have a portion of the funiculus that is adnate (fused to the seed coat), and which forms a longitudinal ridge, or '''raphe''', just above the hilum. In bitegmic ovules (e.g. ''Gossypium'' described here) both inner and outer integuments contribute to the seed coat formation. With continuing maturation the cells enlarge in the outer integument. While the inner epidermis may remain a single layer, it may also divide to produce two to three layers and accumulates starch, and is referred to as the colourless layer. By contrast, the outer epidermis becomes [[tannin|tanniferous]]. The inner integument may consist of eight to fifteen layers.<ref name="kozlowski">{{cite book|title=Seed Biology Volume III|year=1972|publisher=Elsevier|isbn=978-0-323-15067-5|url=https://books.google.com/books?id=Rl04Uvkwq-sC|editor=T.T. Kozlowski|access-date=17 February 2014}}</ref>

As the cells enlarge, and starch is deposited in the outer layers of the pigmented zone below the outer epidermis, this zone begins to lignify, while the cells of the outer epidermis enlarge radially and their walls thicken, with nucleus and cytoplasm compressed into the outer layer. these cells which are broader on their inner surface are called '''palisade''' cells. In the inner epidermis, the cells also enlarge radially with plate like thickening of the walls. The mature inner integument has a palisade layer, a pigmented zone with 15–20 layers, while the innermost layer is known as the fringe layer.<ref name="kozlowski" />

==== Gymnosperms ====

In gymnosperms, which do not form ovaries, the ovules and hence the seeds are exposed. This is the basis for their nomenclature&nbsp;– naked seeded plants. Two sperm cells transferred from the pollen do not develop the seed by double fertilization, but one sperm nucleus unites with the egg nucleus and the other sperm is not used.<ref>{{cite book | author1=Rost, Thomas L. | author2=Weier, T. Elliot | author3=Weier, Thomas Elliot | title=Botany: a brief introduction to plant biology | year=1979 | publisher=Wiley | location=New York | isbn=978-0-471-02114-8 | pages=[https://archive.org/details/botanybriefintro00rost/page/319 319] | url=https://archive.org/details/botanybriefintro00rost/page/319 }}</ref> Sometimes each sperm fertilizes an egg cell and one zygote is then aborted or absorbed during early development.<ref name=Bot2000>{{cite journal |author1=Filonova LH |author2=Bozhkov PV |author3=von Arnold S |title=Developmental pathway of somatic embryogenesis in Picea abies as revealed by time-lapse tracking |journal=J Exp Bot |volume=51 |issue=343 |pages=249–264 |date=February 2000 |pmid=10938831 |doi=10.1093/jexbot/51.343.249 |doi-access= }}</ref> The seed is composed of the embryo (the result of fertilization) and tissue from the mother plant, which also form a cone around the seed in coniferous plants such as [[pine]] and [[spruce]].