In germination the cotyledons come above ground and form the first green leaves of the plant.
The embryo consists of an axis bearing two or more cotyledons and ending below in a radicle; it lies in a generally copious food-storing tissue (endosperm) which is the remains of the female prothallus.
In cases where the development of the embryo is advanced at the resting period, traces run from the cotyledons and determine the symmetry of the stele of the primitive axis, the upperpart of which often shows stem-structure, in some respects at least, and is called the hypocoty- ledonary stem or hypocotyl, while the lower part is the primary root .~-,
In other cases this growing-point becomes active at once, there being little or no elongation of the hypocotyl and tbe cotyledon or cotyledons remaining in the seed.
Toffs is largely developed, and the placenta, so far as known, is nondeciduate, the chorionic villi being either evenly diffused or collected in groups or cotyledons (in Pecora).
The cotyledons contain the valuable linseed oil referred to below.
The embryo consists of an axis bearing one (Monocotyledons) or two (Dicotyledons) cotyledons, which protect the stem bud (plumule) of the future plant, and ending below in a radicle.
In the seed-forming plants (Phanerogams) one or more primary leaves (cotyledons) are already formed in the resting embryo.
The hypocotyl usually elongates, by its cells increasing very greatly in the longitudinal direction both in number and size, so that the cotyledons are raised into the air as the first foliage-leaves.
The name expresses the most universal character of the class, the importance of which was first noticed by John Ray, namely, the presence of a pair of seed-leaves or cotyledons, in the plantlet or embryo contained in the seed.
In germination of the seed the root of the embryo (radicle) grows out to get a holdfast for the plant; this is generally followed by the growth of the short stem immediately above the root, the so-called "hypocotyl," which carries up the cotyledons above the ground, where they spread to the light and become the first green leaves of the plant.
The seeds are filled with the large embryo, the two cotyledons of which are variously folded.
The fruit is usually a capsule opening by valves; the seeds, where four are developed, are each shaped like thy quadrant of a sphere; the seed-coat is smooth, or sometimes warty or hairy; the embryo is large with generally broad, folded, notched or bilobed cotyledons surrounded by a horny endosperm.
The solitary seed has no perisperm or albumen, but has two large and curiously crumpled cotyledons concealing the plumule, the leaves of which, even at this early stage, show traces of pinnae.
Cotyledons opened to show the radicle a, and the plumule.
Flowering plants bear a seed containing an embryo, with usually one or two cotyledons, or seed-leaves; while in flowerless plants there is no seed and therefore no true cotyledon.
The embryo generally fills the seed, and the cotyledons are rolled or folded on each other.
In dicotyledonous plants the first leaves produced (the cotyledons) are opposite.
The greatest merit of this book is the use of the number of cotyledons as a basis of classification; though it must be remembered that the difference between the monocotyledonous and dicotyledonous embryo was detected by Nehemiah Grew.
As the embryo develops it may absorb all the food material available, and store, either in its cotyledons or in its hypocotyl, what is not immediately required for growth, as reserve-food for use in germination, and by so doing it increases in size until it may fill entirely the embryo-sac; or its absorptive power at this stage may be limited to what is necessary for growth and it remains of relatively small size, occupying but a small area of the embryo-sac, which is otherwise filled with endosperm in which the reserve-food is stored.
The seven series of Monocotyledons represent a sequence beginning with the most complicated epigynous orders, such as Orchideae and Scitamineae, and passing through the petaloid hypogynous orders (series Coronarieae) of which Liliaceae is the representative to Juncaceae and the palms (series Calycinae) where the perianth Ioses its petaloid character and thence to the Aroids, screw-pines and albuminous Dicotyledons the cotyledons act as the absorbents of the reserve-food of the seed and are commonly brought above ground (epigeal), either withdrawn from the seed-coat or carrying it upon them, and then they serve as the first green organs of the plant.
The part of the stem below the cotyledons (hypocotyl) commonly plays the greater part in bringing this about.
Exalbuminous Dicotyledons usually store reserve-food in their cotyledons, which may in germination remain below ground (hypogeal).
It is based upon the fact that the histological differentiation of the epidermis of their root is that generally characteristic of Monocotyledons, whilst they have two cotyledons - the old view of the epiblast as a second cotyledon in Gramineae being adopted.
The cotyledons.of Nectandra Puchury were at one time offered in England as nutmegs.
Friedrich Rochleder has described as constituent principles of the cotyledons aphrodaescin, C52H82023, a bitter glucoside, argyraescin, C27 H 42012, aescinic acid, C21H40012, and queraescitrin, C41 H 46025, found also in the leaves.
Seeds albuminous, with one integument; the single embryo, usually bearing two partially fused cotyledons, is attached to a long tangled suspensor.
The bundles from the cotyledons pursue a direct course to the stele of the main axis, and do not assume the girdle-form char acteristic of the adult plant.
A point of anatomical interest is the occurrence in the vascular bundles of the cotyledons, scale-leaves, and elsewhere of a few centripetally developed tracheids, which give to the xylem-strands a mesarch structure such as characterizes the foliar bundles of cycads.
The structure of the seed, the presence of two neck-cells in the archegonia, the late development of the embryo, the partially-fused cotyledons and certain anatomical characters, are features common to Ginkgo and the cycads.
A pair of small strapshaped leaves succeed the two cotyledons of the seedling, and persist as the only leaves during the life of the plant; they retain the power of growth in their basal portion, which is sunk in a narrow groove near the edge of the crown, and the tough lamina, 6 ft.
I I, Bennettites seed in longitudinal section, showing the dicotyledonous embryo; p, cotyledons; r, radicle; s, testa.
Cotyledons two or several.