Wiktionary
n. (context botany English) In plants with seeds, that portion of the embryo or seedling above the cotyledons.
Wikipedia
An Epicotyl is important for the beginning stages of a plants life. It is the region of a seedling stem above the stalks of the seed leaves of an embryo plant. It grows rapidly showing hypogeal germination and extends the stem above the soil surface. Epicotyls also form a hook during hypogeal germination. The epicotyl will expand and form the shoot apex and leaf primordia or "first true leaves"; but the cotyledon will stay below the ground.
In plant physiology, the epicotyl is the embryonic shoot above the cotyledons. In most plants the epicotyl will eventually develop into the leaves of the plant. In dicots, the hypocotyl is what appears to be the base stem under the spent withered cotyledons, and the shoot just above that is the epicotyl. In monocot plants, the first shoot that emerges from the ground or from the seed is the epicotyl, from which the first shoots and leaves emerge.
Lengthening of the epicotyl is thought to be controlled by the phytochrome photoreceptors.
Usage examples of "epicotyl".
The fact of so many organs of different kinds--hypocotyls and epicotyls, the petioles of some cotyledons and of some first leaves, the cotyledons of the onion, the rachis of some ferns, and some flowerstems--being all arched whilst they break through the ground, shows how just are Dr.
Although this movement, in its ordinary or unmodified state, appears in some cases to be of service to plants, either directly or indirectly--for instance, the circumnutation of the radicle in penetrating the ground, or that of the arched hypocotyl and epicotyl in breaking through the surface--yet circumnutation is so general, or rather so universal a phenomenon, that we cannot suppose it to have been gained for any special purpose.
As the arched epicotyl, in whatever position it may be placed, bends quickly upwards through apogeotropism, and as the two legs tend at a very early age to separate from one another, as soon as they are relieved from the pressure of the surrounding earth, it was difficult to ascertain positively whether the epicotyl, whilst remaining arched, circumnutated.
The sheathlike cotyledons of the Gramineae circumnutate, that is, move to all sides, as plainly as do the hypocotyls or epicotyls of any dicotyledonous plants.
When the cotyledons are hypogean, that is, remain buried in the soil, the hypocotyl is hardly developed, and the epicotyl or plumule rises in like manner as an arch through the ground.
In consequence of this injury it had emitted near the hypogean cotyledons two secondary shoots, and it was remarkable that both of these were arched, like the normal epicotyl in ordinary cases.
WE have seen in the first chapter that the stems of all seedlings, whether hypocotyls or epicotyls, as well as the cotyledons and the radicles, are continually circumnutating--that is they grow first on one side and then on another, such growth being probably preceded by increased turgescence of the cells.
In rarely or never becoming perfectly straight, these cotyledons differ remarkably from the ultimate condition of the arched hypocotyls or epicotyls of dicotyledons.
Yet we should remember that the circumnutating sheathlike cotyledons of Phalaris, the hypocotyls of Solanum, and the epicotyls of Asparagus formed round themselves little circular cracks or furrows in a superficial layer of damp argillaceous sand.
After hypocotyls or epicotyls have emerged from the ground, they quickly become perfectly straight.
In concluding this section of the present chapter it may be convenient to summarise, under the form of an illustration, the usual movements of the hypocotyls and epicotyls of seedlings, whilst breaking through the ground and immediately afterwards.
THE radicles, hypocotyls and epicotyls of seedling plants, even before they emerge from the ground, and afterwards the cotyledons, are all continually circumnutating.
That the movements of leaves and cotyledons which do not sleep come within the class of circumnutating movements cannot be doubted, for they are closely similar to those of hypocotyls, epicotyls, the stems of mature plants, and of various other organs.
The epicotyls bowed themselves towards the light so rapidly that in little more than 3 h.
After the epicotyls had bowed themselves to the full extent towards the light, ellipses of considerable size were described in the usual manner.