Cotyledons
The cotyledon or the cotyledo (plural cotyledons), also cotyledon , earlier seed lobes , is the leaf of the plant embryo . Naked-seed plants usually have two to numerous cotyledons. The bedecktsamer were traditionally subdivided into the monocotyledons with one and the dicotyledons with two cotyledons, a systematic subdivision that has essentially remained until today (with the exception of the basal orders ).
However, there are very seldom species with more than two cotyledons, as in the family of the Olacaceae or in some species of the cola in the family of the mallow family .
Development of a cotyledon
The embryogenesis of Arabidopsis thaliana has three characteristic morphological on stadiums. First, through a precise pattern of cells that initially divide synchronously, a radially symmetrical cell sphere is created, which is called the globular stage of the embryo. Next, the cotyledon primordia arise through rapid cell division in two areas on each side of the future apex of the shoot axis . The bilaterally symmetrical heart stage is formed . Finally, through elongation of the axis and further development of the cotyledons, the torpedo stage of the embryo develops . In many species, after the torpedo stage, the cotyledons grow considerably, increasing cell number and size until they make up almost 90% of the total embryo mass.
Most cotyledons are severely reduced leaves; Known exceptions are the slightly pinnate cotyledons of the garden cress or the strongly developed cotyledons of Ricinus .
Special functions
Cotyledons are the first leaves of a germinating plant. They sit on a special axis segment, the hypocotyl . With epigeic (above-ground) germination, such as with radishes , they get from the seed coat over the surface of the earth, turn green there and then contribute to the production of nutrients. In the case of hypogean (underground) germination, on the other hand, as in the case of the coarse bean , they remain in the seed coat, where they either function as haustorial organs that absorb nutrients from the surrounding nutrient tissue , or they are already storage organs themselves, such as in the legume family . Beans and peas are mainly consumed for their protein-rich cotyledons.
From the plumula already created between the cotyledons , the green leaves unfold, the first of which are called primary leaves .
designation
The name is derived from the ancient kotyle / cotyle / cotylicus (κοτύλη), which referred to a bowl-shaped drinking vessel (see Skyphos ) and, derived from it, a measure of capacity , which was measured with such a (calibrated) vessel (about 270 cubic centimeters). The name was adapted in the early modern period as a medical term for the placental lobes of the uterus. Carl von Linné introduced them into botany in 1735 as a supposedly analogous formation to the embryos of ruminants ( endometrium ) as cotyledons .
Nathaniel Highmore recognized the cotyledons as leaves in 1651; In 1682 Nehemiah Grew called them the lobes of the seed , in the same year John Ray called them folia seminalia ( seed leaves ).
literature
- Troll, Wilhelm: Practical introduction to plant morphology. First part: the vegetative construction. Gustav Fischer Verlag Jena, 1954
- Troll, Wilhelm: Practical introduction to plant morphology. Second part: the flowering plant. Gustav Fischer Verlag Jena, 1957
Individual evidence
- ↑ a b Gerhard Wagenitz : Dictionary of Botany. The terms in their historical context. 2nd, expanded edition. Spektrum Akademischer Verlag, Heidelberg / Berlin 2003, ISBN 3-8274-1398-2 , p. 179.
- ↑ Duden. The German spelling . 22nd edition, Dudenverlag, Mannheim etc. 2000. ISBN 3-411-04012-2
- ^ Manfred A. Fischer , Karl Oswald, Wolfgang Adler: Excursion flora for Austria, Liechtenstein and South Tyrol. 3rd, improved edition. State of Upper Austria, Biology Center of the Upper Austrian State Museums, Linz 2008, ISBN 978-3-85474-187-9 , p. 1280.
- ↑ Kenneth R. Robertson: The Genera of the Olacaceae in the Southestern United States. In: Journal of the Arnold Arboretum. 63 (1), 1982, pp. 387-393, at p. 389, online at biodiversitylibrary.org.
- ^ Encyclopedia Britannica online
