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 ).
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.
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.
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 .
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