A seed coat or testa (Latin: vessel, shell) also episperm or outdated also spermoderm , shelves or tunica (externa) and lorica , surrounds and protects the embryo located inside . After fertilization of the ovule, it is formed from the integument surrounding the ovule . The seed coat can be hard and crust-like, woody or bone-like, thin or tender-skinned, dry or less often fleshy, it can also grow winged or even hairy.
If the seed coat can be divided into two different, separable layers, the inner layer is called tegmen ( glass skin, inner skin, core skin) and the outer one is called testa .
The outermost layer of the epidermis is here as Exotesta and the innermost as endotesta referred. In between there can be one or more layers, which are collectively referred to as the mesotesta .
If the seed coat is very hard, it is called a sclerotesta (Greek / Latin: dry, hard vessel). Often the hard shell is formed by the coalesced seed and fruit pods. The seed coat can also differentiate into an inner and hard, heavily lignified sclerotesta and a fleshy outer sarcotesta .
If the seed coat contains a high proportion of sugars, which swell to form a mucus when germinated, it is called a myxotesta ( sticky seed ), as with the tomato and a few other species.
In addition to protecting the embryo, the seed coat can serve to spread the seed through the formation of certain structures :
- So are z. B. to evaluate the hair of the cotton seed as derivatives of the seed coat. These are originally in the service of the spreading of the cotton seed by the wind (called anemochory ).
- Another example is the red fleshy structures that surround the seeds of the yew tree ( Taxus baccata ). This is not a fruit in the botanical sense, but a transformation of the seed coat into a so-called aril , which is used to attract animals (here mainly birds), which after digestion of the red, fleshy aril elsewhere excrete with the feces and thus contribute to the spread of the seed ( zoochory ).
However, seeds without a seed coat are also possible, as in the case of the genus Santalum . Here the seeds are “directly” in the stone core or endocarp .
- ↑ HA Pierer (Ed.): Universal Lexicon of the Present and Past. Volume 26, 2nd edition, 1845, p. 276, limited preview in the Google book search.
- ^ Peter Sitte , Elmar Weiler , Joachim W. Kadereit , Andreas Bresinsky , Christian Körner : Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X , p. 776 .