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The evolution of having one or two cotyledons may have arisen 200-150 Mya when monocots and dicots are thought to have diverged. [ 3 ] [ 4 ] Furthermore, the cotyledons in dicot seeds contain the endosperm which acts as the seed’s food storage, while in monocot the endosperm is separated from the cotyledon. [ 1 ]
It is given this name in eudicots because most plants from this group have two cotyledons, giving the embryo a heart shaped appearance. The shoot apical meristem is between the cotyledons. Stage IV, in the illustration above, indicates what the embryo looks like at this point in development. 5 indicates the position of the cotyledons.
An endosperm is formed after the two sperm nuclei inside a pollen grain reach the interior of a female gametophyte or megagametophyte, also called the embryonic sac.One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell (its nucleus is often called the triple fusion nucleus).
The scutellum (from the Latin scutella meaning "small shield") can also refer to the equivalence of a thin cotyledon in monocots (especially members of the grass family). It is very thin with high surface area, and serves to absorb nutrients from the endosperm during germination. [2] [full citation needed] [page needed]
As the plant embryo grows at germination, it sends out a shoot called a radicle that becomes the primary root, and then penetrates down into the soil.After emergence of the radicle, the hypocotyl emerges and lifts the growing tip (usually including the seed coat) above the ground, bearing the embryonic leaves (called cotyledons), and the plumule that gives rise to the first true leaves.
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Endosperm 2. Zygote 3. Embryo 4. Suspensor 5. Cotyledons 6. Shoot Apical Meristem 7. Root Apical Meristem 8. Radicle 9. Hypocotyl 10. Epicotyl 11. Seed Coat. Angiosperm seeds are "enclosed seeds", produced in a hard or fleshy structure called a fruit that encloses them for protection. Some fruits have layers of both hard and fleshy material.
A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both regions overlap. The region of overlap is called a vegetation tension zone.