Germination is often slower where there is a store of available food in the perisperm, or in the endosperm, or in the embryo itself, than where this is scanty or wanting.
Within these is the albumen or endosperm, constituting the flowery part of the seed.
In many aquatic plants, the endosperm of the seed is absent or very scanty.
If in its extension to contain the new formations within it the embryo-sac remains narrow, endosperm formation proceeds upon the lines of a cell-division, but in wide embryo-sacs the endosperm is first of all formed as a layer of naked cells around the wall of the sac, and only gradually acquires a pluricellular character, forming a tissue filling the sac. The function of the endosperm is primarily that of nourishing the embryo, and its basal position in the embryo-sac places it favourably for the absorption of food material entering the ovule.
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.
They are present from the beginning of the development of the cell-wail, and arise from the spindle fibres, all of which may be continued as connecting threads (endosperm of Tamus communis), or part of them may be overlaid by cellulose lamellae (endosperm of Lilium Martagon), or they may be all overlaid as in pollen mother-cells and pollen grains of Helleborus foetidus.
6, 3); the seeds contain a small embryo in a copious fleshy or cartilaginous endosperm.
A large distinct leafy embryo lies in the middle of a dense, oily tissue (endosperm).
The gametophyte or prothallial generation is thus extremely reduced, consisting of but little more than the male and female sexual cells - the two sperm-cells in the pollen-tube and the egg-cell (with the synergidae) in the embryo-sac. At the period of fertilization the embryo-sac lies in close proximity tube has penetrated, the separating cell-wall becomes absorbed, and the male or sperm-cells are ejected into the embryosac. Guided by the synergidae one male-cell passes into the oosphere with which it fuses, the two nuclei uniting, while the other fuses with the definitive nucleus, or, as it is also called, the endosperm nucleus.
The endosperm-nucleus divides rapidly to produce a cellular tissue which fills up the interior of the rapidly-growing embryosac, and forms a tissue, known as endosperm, in which is stored a supply of nourishment for the use later on of the embryo.
It has long been known that after fertilization of the egg has taken place, the formation of endosperm begins from the endosperm nucleus, and this had come to be regarded as the recommencement of the development of a prothallium after a pause following the reinvigorating union of the polar nuclei.
If, on the other hand, the endosperm is the product of an act of fertilization as definite as that giving rise to the embryo itself, we have to recognize that twin-plants are produced within the embryo-sac - one, the embryo, which becomes the angiospermous plant, the other, the endosperm, a short-lived, undifferentiated nurse to assist in the nutrition of the former, even as the subsidiary embryos in a pluri-embryonic Gymnosperm may facilitate the nutrition of the dominant one.
If this is so, and the endosperm like the embryo is normally the product of a sexual act, hybridization will give a hybrid endosperm as it does a hybrid embryo, and herein (it is suggested) we may have the explanation of the phenomenon of xenia observed in the mixed endosperms of hybrid races of maize and other plants, regarding which it has only been possible hitherto to assert that they were indications of the extension of the influence of the pollen beyond the egg and its product.
The idea of the endosperm as a second subsidiary plant is no new one; it was suggested long ago in explanation of the coalescence of the polar nuclei, but it was then based on the assumption that these represented male and female cells, an assumption for which there was no evidence and which was inherently improbable.
The developing embryo at the end of the suspensor grows out to a varying extent into the forming endosperm, from which by surface absorption it derives good material for growth; at the same time the suspensor plays a direct part as a carrier of nutrition, and may even develop, where perhaps no endosperm is formed, special absorptive "suspensor roots" which invest the developing embryo, or pass out into the body and coats of the ovule, or even into the placenta.
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 position of the embryo in relation to the endosperm varies, sometimes it is internal, sometimes external, but the significance of this has not yet been established.
The formation of endosperm starts, as has been stated, from the endosperm nucleus.
In cases where the embryo has stored reserve food within itself and thus provided for self-nutrition, such endosperm as remains in the seed may take on other functions, for instance, that of water-absorption.
In two Malayan species of Balanophora, the embryo is developed from a cell of the endosperm, which is formed from the upper polar nucleus only, the egg apparatus becoming disorganized.
As the development of embryo and endosperm proceeds within the embryo-sac, its wall enlarges and commonly absorbs the substance of the nucellus (which is likewise enlarging) to near its outer limit, and combines with it and the integument Fruit and to form the seed-coat; or the whole nucellus and even the integument may be absorbed.
Seeds in which endosperm or perisperm or both exist are commonly called albuminous or endospermic, those in which neither is found are termed exalbuminous or exendospermic. These terms, extensively used by systematists, only refer, however, to the grosser features of the seed, and indicate the more or less evident.
occurrence of a food-reserve; many so-called exalbuminous seeds show to microscopic examination a distinct endosperm which may have other than a nutritive function.
The presence or absence of endosperm, its relative amount when present, and the position of the embryo within it, are valuable characters for the distinction of orders and groups of orders.
In albuminous Monocotyledons the cotyledon itself, probably in consequence of its terminal position, is commonly the agent by which the embryo is thrust out of the seed, and it may function solely as a feeder, its extremity developing as a sucker through which the endosperm is absorbed, or it may become the first green organ, the terminal sucker dropping off with the seed-coat when the endosperm is exhausted.
The kernel consists mainly of the abundant endosperm, which is firm, whitish in colour and marbled with numerous reddish-brown vein-like partitions, into which the inner seedcoat penetrates, forming what is known botanically as ruminated endosperm.
The testa is thin and membranous but occasionally coloured, and the embryo small, the great bulk of the seed being occupied by the hard farinaceous endosperm (albumen) on which the nutritive value of the grain depends.
Its position is remarkable, closely applied to the surface of the endosperm at the base of its outer side.
The part in contact with the endosperm is plate-like, and is known as the scutellum; the surface in contact with the endosperm forms an absorptive epithelium.
1, back, and 2, front view; 3, vertical section, showing (b) the endosperm, and (a) embryo; 4, beginning of germination, showing (b) the pileole and (c) the radicle and secondary rootlets surrounded by their coleorrhizae.
The scutellum meanwhile feeds the developing embryo from the endosperm.
best distinctions are found in the position of the embryo in relation to the endosperm - lateral in grasses, basal in Cyperaceae - and in the possession by Gramineae of the 2-nerved palea below each flower.
In the ripe seed the integument assumes the form of a fleshy envelope, succeeded internally by a hard woody shell, internal to which is a thin papery membrane - the apical portion of the nucellus - which is easily dissected out as a conical cap covering the apex of the endosperm.
The endosperm detached from a large Ginkgo ovule after fertilization bears a close resemblance to that of a cycad; the apex is occupied by a depression, on the floor of which two small holes mark the position of the archegonia, and the outgrowth from the megaspore apex projects from the centre as a short peg.
A papery remnant of nucellus lines the inner face of the woody shell, and, as in cycadean seeds, the apical portion is readily separated as a cap covering the summit of the endosperm.
In the Abietineae the cells of the middle tier elongate and push the lowest tier deeper into the endosperm; the cells of the bottom tier may remain in lateral contact and produce together one embryo, or they may separate (Pinus, Juniperus, &c.) and form four potential embryos.
The outermost layer of the endosperm consists of square cells larger and more regular in form than those on each side; these contain aleuron grains - small particles of gluten or nitrogenous matter.
that an approximate notion C, Cells of endosperm or albumen, of the richness in albufilled with starch.
- Vertical section of the ovule of the Scotch Fir (Pinus sylvestris) in May of the second year, showing the enlarged embryo-sac b, full of endosperm cells, and pollen-tubes c, penetrating the summit of the nucellus after the pollen has entered the large micropyle.
The seeds contain a large embryo and no endosperm.
Even the most delicate tissues, such as cambium and phloem, the endosperm of seeds, or the formative tissue of the growing-point, are frequently preserved cell for cell, both in calcareous and silicious material.
endosperm of hard wheat 's.
endosperm of the wheat grain contains all the material used by the baker.
Brown flour - produced through the inclusion of bran along with the white endosperm.
White flour - made from the starchy endosperm only; bran and germ are removed as co-products.
endosperm fraction and further processing of the starch fraction yields glucose syrups.
There was modest improvement in blood iron levels, showing that iron in rice endosperm is absorbed by the body.
Farina - Coarsely ground endosperm of hard wheat's.
engineering the provitamin A (b-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm.
The fruit is berry-like, and the seeds are remarkable for having their embryo surrounded by an endosperm as well as by a perisperm.
Endosperm is formed as the result of the fusion of the second male cell with the so-called definitive nucleus of the embryo-sac (see ANGlOSPERMS).
The embryo is generally surrounded by a larger or smaller amount of foodstuff (endosperm) which serves to nourish it in its development to form a seedling when the seed germinates; frequently, however, as in pea or bean and their allies, the whole of the nourishment for future use is stored up in the cotyledons themselves, which then become thick and fleshy.
In some plants the nucellus is not thus absorbed, but itself becomes a seat of deposit of reserve-food constituting the perisperm which may coexist with endosperm, as in the water-lily order, or may alone form a food-reserve for the embryo, as in Canna.
Three must be considered: (I) the scutellum, connected by vascular tissue with the vascular cylinder of the main axis of the embryo which it more or less envelops; it never leaves the seed, serving merely to prepare and absorb the food-stuff in the endosperm; (2) the cellular outgrowth of the axis, the epiblast, small and inconspicuous as in wheat, or larger as in Stipa; (3) the pileole or germ-sheath, arising on the same side of the axis and above the scutellum, enveloping the plumule in the seed and appearing above ground as a generally colourless sheath from the apex of which the plumule ultimately breaks (fig.
Their internal structure is sometimes admirably preserved, so that the endosperm with its archegonia is clearly shown (fig.
When all three parts of the grain (the germ, bran, and endosperm) are present in their original proportions after milling, the grain is still a whole grain.
White flour is milled only from the endosperm.
Germ flour is made from the endosperm and the germ part of the wheat grain.
Whole grains are grains that still have the entire kernel including the bran, germ, and endosperm intact.
It is produced from the endosperm of cluster or guar beans.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.