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2.Various Stages in the Nuclear Division of the Pollen i Mother-cells of Lilium.
Rosenberg (1909) adduces evidence fox the existence of chromosomes or prochromosomes in resting nuclei in a large number of plants, but most observers consider that the chromosomes during the resting stage become completely resolved into a nuclear network in which no trace of the original chromosomes can be seen.
C) have shown that, in some forms at any rate, the finer structure and detailed development of the nuclear apparatus is extremely complex.
Nuclear Division.The formation of new cells is, in the case of tminucleate cells, preceded by or accompanied by the division of the nucleus.
It is clear, however, that an equal quantitative division and distribution of the chromatin to the daughter cells is brought about; and if, as has been suggested, the chromatin consists of minute particles or units which are the carriers of the hereditary characteristics, the nuclear division also probably results in the equal division and distribution of one half of each of these units to each daughter cell.
D, Nuclear cavity with chromosomes.
If the white cells be required, as in local suppurating abscess, general septicaemia, acute pneumonia, &c., there is an active proliferation of the myelocytes to form the polymorpho-nuclear leucocytes, so that we have in this condition a leucoblastic transformation of the fatty marrow.
Varies in shape, but is usually round or oval, and is sharply defined by a nuclear membrane from the cytoplasm in which it lies.
The nucleus in its vegetative stage shows a fine network throughout containing in the meshes the so-called nuclear-sap; attached to the network are the chromosomes, in the form of small irregular masses, which have a strong affinity for the " basic dyes."
Division of the nucleolus and formation of nuclear plate.
The daughter nuclei may have arrived at the anaphase stage, and have even gone the length of forming a nuclear membrane, without an equatorial depression having shown itself in the cell-body.
This call is immediately answered by an active proliferation and steady maturing of the myclocytes in the marrow to form the polymorpho-nuclear leucocytes.
It has been proved that the pyo-genic bacterial toxins, if not too concentrated, will attract the polymorpho-nuclear leucocytes, but if concentrated, may have a repelling influence.
The vanguard of this advancing army is composed of a more or less compact layer of the mono-nuclear phagocytes (polyblasts) accompanied by numerous new vessels.
A small cellular area formed by emigrated polymorpho nuclear leucocytes surrounding a central mass of bacteria.
252; Schottlander, " Nuclear and Cell Division in Epithelium of Inflamed Skin," Arch.
Rutherford had announced the nuclear theory of atomic structure which required each atom to consist of a minute positively charged nucleus about which negative electrons were distributed.
In certain forms the occurrence of prominent myonemes or muscle-fibrillae has been described, and, moreover, a nuclear origin assigned to them also.
A Trypanosome always possesses two distinct nuclear bodies, one the trophonucleus, regulating the trophic life of the cell, the other, the kinetonucleus, directing its locomotor activities.
The nucleolus appears to form a part of t-he Linin network, but has usually also a strong affinity for nuclear stains.
It forms a part of the 1mm or plastin network of the nucleus and may become impregnated with varying quantities of chromatin stored up for use in the formation of the chromosomes and other nuclear activities.
Coincident with these changes the nuclear membrane disappears and a spindle-shaped or barrelshaped group of threads makes its appearance in.
2, L), a nucleolus appears, a nuclear membrane is formed, and daughter nuclei are thus constituted which possess the same structure and staining reactions as the mother nucleus.
In order to effect this the individual chromosomes must become associated in some way, for there is no diminution in the actual amount of nuclear substance, and this leads to certain modifications in the division which are not seen in the vegetative nuclei.
Cell Division.With the exception of a few plants among the Thallophytes, which consist of a single multinucleate cell, Caulerpa, Vaucheria, &c., the division of the nucleus is followed by the division of the cell either at once, in uninucleate cells, or after a certain number of nuclear divisions, in multinucleate cells.
The strongest direct evidence seems to be that the nuclear substances are the only parts of the cells which are always equivalent in quantity, and that in the higher plants and animals the male organ or spermatozoid is composed almost entirely of the nucleus, and that the male nucleus is carried into the female cell without a particle of cytoplasm.i Since, however, the nucleus of the female cell is always accompanied by a larger or smaller quantity of cytoplasm, and that in a large majority of the power plants and animals the male cell also contains cytoplasm, it cannot yet be definitely stated that the cytoplasm does not play some part in the process.
Some observers consider that the yeast nucleus possesses a typical nuclear structure, and exhibits division by mitosis, but the evidence for this is not very satisfactory.
The polymorpho-nuclear leucocytes are seen in great numbers in the blood vessels.
To replace this cellular destruction there has been a demand for reinforcements on the home centres of the polymorpho-nuclear leucocytes - the bone marrow.
It had been suggested, and Bohr had adopted this view, that the nuclear charge was equal to the atomic number, i.e.