Editing Seed (section)

=== Seed coat ===
{{see also|Scarification (botany)}}
[[File:Pomegranate arils.jpg|thumb|Seed coat of pomegranate]]

The seed coat develops from the maternal tissue, the [[integument]]s, originally surrounding the ovule. The seed coat in the mature seed can be a paper-thin layer (e.g. [[peanut]]) or something more substantial (e.g. thick and hard in [[honey locust]] and [[coconut]]), or fleshy as in the [[sarcotesta]] of [[pomegranate]]. The seed coat helps protect the embryo from mechanical injury, predators, and drying out. Depending on its development, the seed coat is either '''bitegmic''' or '''unitegmic'''. Bitegmic seeds form a testa from the outer integument and a tegmen from the inner integument while unitegmic seeds have only one integument. Usually, parts of the testa or tegmen form a hard protective mechanical layer. The mechanical layer may prevent water penetration and germination. Amongst the barriers may be the presence of [[lignified]] [[sclereids]].<ref>{{cite web|url=http://5e.plantphys.net/article.php?ch=23&id=8&search=seed|title=Sinauer Associates, Inc., Publishers|website=5e.plantphys.net|access-date=7 May 2018|url-status=live|archive-url=http://archive.wikiwix.com/cache/20140122033254/http://5e.plantphys.net/article.php?ch=23&id=8&search=seed|archive-date=22 January 2014}}</ref>

The outer integument has a number of layers, generally between four and eight organised into three layers: (a) outer epidermis, (b) outer pigmented zone of two to five layers containing [[tannin]] and starch, and (c) inner epidermis. The '''endotegmen''' is derived from the inner epidermis of the inner integument, the '''exotegmen''' from the outer surface of the inner integument. The '''endotesta''' is derived from the inner epidermis of the outer integument, and the outer layer of the testa from the outer surface of the outer integument is referred to as the '''exotesta'''. If the exotesta is also the mechanical layer, this is called an exotestal seed, but if the mechanical layer is the endotegmen, then the seed is endotestal. The exotesta may consist of one or more rows of cells that are elongated and pallisade like (e.g. [[Fabaceae]]), hence 'palisade exotesta'.<ref>{{cite web|url=http://archive.gramene.org/db/ontology/search?id=PO:0006048|title=plant_anatomy Term "seed coat epidermis" (PO:0006048)|work=gramene.org|url-status=live|archive-url=https://web.archive.org/web/20140203143705/http://archive.gramene.org/db/ontology/search?id=PO:0006048|archive-date=2014-02-03}}</ref><ref>{{cite book|title=6 – Seed and fruit – University Publishing Online – Paula J. Rudall. Anatomy of Flowering Plants: An Introduction to Structure and Development. Third edition|publisher=Cambridge University Press |date=2007|isbn=978-0-521-69245-8|doi=10.1017/CBO9780511801709|last1=Rudall|first1=Paula J.}}</ref>

In addition to the three basic seed parts, some seeds have an appendage, an '''[[aril]]''', a fleshy outgrowth of the funicle ([[ovule|funiculus]]), (as in [[Taxus|yew]] and [[nutmeg]]) or an oily appendage, an '''[[elaiosome]]''' (as in ''[[Corydalis]]''), or hairs (trichomes). In the latter example these hairs are the source of the textile crop [[cotton]]. Other seed appendages include the raphe (a ridge), wings, '''caruncles''' (a soft spongy outgrowth from the outer integument in the vicinity of the micropyle), spines, or tubercles.

A scar also may remain on the seed coat, called the '''[[Hilum (biology)|hilum]]''', where the seed was attached to the ovary wall by the funicle. Just below it is a small pore, representing the micropyle of the ovule.