Nuclei are everywhere present.
here structures have been observed which resemble nuclei in some of their characteristics.
As before, only true ring nuclei, and not internal anhydrides of aliphatic compounds, will be mentioned.
True ring systems, which possess the characters of organic nuclei, do not come into existence in threeand four-membered rings, their first appearance being in penta-atomic rings.
The nuclei of the original cells persist in the protoplasmic membrane.
The cells concerned, like all secreting organs, have abundant protoplasm with large nuclei, and sometimes, in addition, part of the cell-wall is modified as a filter.
This is a necessary consequence of the fusion of two nuclei in fertilization, unless the chromosomes are to be doubled at each generation.
The following diagrams illustrate these statements: - C ` H C OH HC /CH HC CH HC,/CH 'N/ HC CH CH CH From the benzene nucleus we can derive other aromatic nuclei, graphically represented by fusing two or more hexagons along common sides.
They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
1.Reconstruction of the daughter nuclei of Phaseolus.
The cells in which the fungoid organism is vigorously flourishing are exceedingly active, showing large size, brilliant nuclei, protoplasm and vacuole, all of which give signs of iptense metabolic activity.
reduction in size is due to A, Two vermiform nuclei in the emthe absence of cytoplasm, bryo sac; one approaching the eggwhich is in some cases so nucleus, the other uniting with the 11 ~ ~h ~h upper polar nucleus.
7, A) nuclei, which may be regarded as physiologically equivalent to a sexual fusion.
Here we meet with a great diversity of types: oxygen, nitrogen, sulphur and other elements may, in addition to carbon, combine together in a great number of arrangements to form cyclic nuclei, which exhibit characters closely resembling open-chain compounds in so far as they yield substitution derivatives, and behave as compound radicals.
B~it the staining reactions of nuclei may vary at different stages of their development; and it i~ probable that there is no method of staining which differentiates with certainty the various morphological constituents of the nucleus.
The union of the germ nuclei has now been observed in all the main groups of Angiosperms, Gymnosperms, Ferns, Mosses, Algae and Fungi, and presents a striking resemblance in all.
In the first, a cleavage follows each nuclear division; in the second, the nuclei multiply by division a number of times, and then the ovum divides into as many blastomeres as there are nuclei present.
The protoplasm of a living cell con.sists of a semifluid granular substance, called the cytoplasm, one or more nuclei, and sometimes centrosomes and plastids.
The second ~r hoinotype division which immediately follows reverts to the normal type except that the already split chromosomes at once separate to form the daughter nuclei without the intervention of a resting stage.
The segmentation of the fertilized nucleus results in the formation of a number of nuclei which arrange themselves around the periphery of the egg and, the protoplasm surrounding them becoming constricted, a blastoderm or layer of cells, enclosing the central yolk, is formed.
The food so absorbed passes to the outer cortical mycellum, and from this tc the inner hyphae, which appear to be the organs of the interchangi of substance, for they are attracted to the neighborhood of thi nuclei of the cells, which they enter, and iii which they form agglom erations of interwoven filaments.
In Fucus and allied forms the spindle-fibres between the daughter nuclei disappear early and the new cell-wall is formed in the cytoplasm.
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 the higher plants, after the separation of the daughter nuclei, minute granular swellingc appear, in the equatorial region, on the connecting fibres which still persist between the two nuclei, to form what is called the cell-plate.
(1898); Sargant, The Formation of the Sexual Nuclei in Liiium Martagon, I.
In plants with multinucleate cells, such as Albugo, Peronospora and Vaucheria, it is usually a uninucleate cell differentiated by separation of the nuclei from a multinucleate cell, but in Albugo bliti it is multinucleate, and in Sphaero plea it may contain more than one nucleus.
Fertilization is effected by the union of two nuclei in all those cases which have been carefully investigated.
In a few cases both among the higher and the lower plants, of which the formation of spores in the ascus is a typical example, new cells are formed by the aggregation of portions of the cytoplasm around the nuclei which become delimited from the rest of the cell iontents by a membrane.
complete sexual differenti- C, Fusion of the germ nuclei in the ation the egg-cell is quies- egg-cell.
The sieve tubes contain a thin lining layer of protoplasm on their walls, but no nuclei, and the cell sap contains albuminous substances which are coagulable by heat.
Within the yolk the nuclei of some "yolk cells" can be distinguished.
It may be noticed here that cyclic nuclei can only contain the groups > CH 2.
It appears that in parthenogenetic eggs two polar nuclei are formed.
Deferring the detailed discussion of cyclic or ringed hydrocarbons, a correlation of the various types or classes of compounds which may be derived from hydrocarbon nuclei will now be given.
Dumas went no further that thus epitomizing his observations; and the next development was made in 1836 by Auguste Laurent, who, having amplified and discussed the applicability of Dumas' views, promulgated his Nucleus Theory, which assumed the existence of " original nuclei or radicals " (radicaux or noyaux fondamentaux) composed of carbon and hydrogen, and " derived nuclei " (radicaux or noyaux derives) formed from the original nuclei by the substitution of hydrogen or the addition of other elements, and having properties closely related to the primary nuclei.
Bamberger's observations on reduced quinoline derivatives point to the same conclusion, that condensed nuclei are not benzenoid, but possess an individual character, which breaks down, however, when the molecule is reduced.
During recent years an immense number of ringed or cyclic compounds have been discovered, which exhibit individual characters more closely resembling benzene, naphthalene, &c. than purely aliphatic substances, inasmuch as in general they contain double linkages, yet withstand oxidation, and behave as nuclei, forming derivatives in much the same way as benzene.
Most of the simple ring systems which contain two adjacent carbon atoms may suffer fusion with any other ring (also containing two adjacent carbon atoms) with the production of nuclei of greater complexity.
The more important types are derived from aromatic nuclei, benzene, naphthalene, &c.; the ortho-di-derivatives of the first named, lending themselves particularly to the formation of condensed nuclei.
Thus ortho-phenylene diamine yields the following products: N H N ./`N; Xn NZ In some cases oxidation of condensed benzenoid-heterocyclic nuclei results in the rupture of the heterocyclic ring with the formation of a benzene dicarboxylic acid; but if the aromatic nucleus be weakened by the introduction of an amino group, then it is the benzenoid nucleus which is destroyed and a dicarboxylic acid of the heterocyclic ring system obtained.
These consist of enormous cells with nuclei so large as to be in some cases just visible to the naked eye.
+1~ ii 1n a, Antipodal cell; sp, polar nuclei; eing e sma er.
The Nuclei of the Lower Plants.It is only in comparatively recent times that it has been possible to determine with any degree of certainty that the minute deeply stainable bodies described more especially by Schmitz (1879) in many Algae and Fungi could be regarded as true nuclei.
In the egg of these insects a small number of nuclei are formed by the division of the nucleus, and each of these nuclei originates by division the cell-layers of a separate embryo.
By fusing two nuclei we obtain the formula of naphthalene, C 1 oH 8; by fusing three, the hydrocarbons anthracene and phenanthrene, C14H10; by fusing four, chrysene, C18H12, and possibly pyrene, C16H1n; by fusing five, picene, C22 H 14.
Other hydrocarbon nuclei generally classed as aromatic in character result from the union of two or more benzene nuclei joined by one or two valencies with polymethylene or oxidized polymethylene rings; instances of such nuclei are indene, hydrindene, fluorene, and fluoranthene.
From these nuclei an immense number of derivatives may be obtained, for the hydrogen atoms may be substituted by any of the radicals discussed in the preceding section on the classification of organic compounds.
Such condensed nuclei are, in many cases, more readily obtained than the parent nucleus.
Systems which are generally unsaturated compounds, often of considerable stability, and behave as nuclei; these compounds constitute a well-individualized class exhibiting closer affinities to benzenoid substances than to the open-chain series.
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.
The two nuclei are successively divided from the egg nucleus in the usual way, but they frequently become absorbed in the peripheral protoplasm instead of being extruded from the egg-cell altogether.
By passing the vapour of this compound through a red-hot tube, it yields the isomeric a0- pyridylpyrrol, the potassium salt of which with methyl iodide gives a substance methylated both in the pyridine and pyrrol nuclei.
In some species (Ascaris decipiens) the giant cell is replaced by an irregular mass of protoplasm containing a number of small nuclei.
There are several nuclei.
of the chromatic substance between the two daughter nuclei.
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.
The old system of locating immigrants in colonies, or colonial nuclei, which involved an enormous outlay of money with but slight benefit to the country, has been superseded by a system of locating the immigrants on the large plantations under formal contracts.
After the division and cleavage of the chromosomes of the original nucleus have taken place they pass from the equator to the poles of the spindle, rearranging themselves close to the separated centrosomes to form daughter nuclei.
Some pathological cells, such as the giant-cells of tumours, of bone, and those of tubercle, are polynucleated; in some instances they may contain as many as thirty or more nuclei.
It consists in an unequal number of chromosomes passing over to each of the daughter nuclei, so that one may become hypochromatic, the other hyperchromatic. When this happens the resulting cleavage of the cytoplasm and nucleus is also unequal.
- Polynucleated cell with nuclei of normal size arising from multiple karyokinetic division.
- Multinucleated giant-cell, the nuclei small and produced amitotically.
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.
Some of the nuclei within multinucleated cells may occasionally be engaged in mitotic division, the others being in the resting state.
We have analogies to this in the two nuclei of some of the protozoa, the one being solely for the purpose of propagation, the other being associated with the functional activities of the cell.
It is convenient to distinguish between aliphatic and aromatic acids; the first named being derived from open-chain hydrocarbons, the second from ringed hydrocarbon nuclei.
In the same way, by electrolysing a mixture of a metallic salt and an ester, other nuclei may be condensed; thus potassium acetate and potassium ethyl succinate yield CH 3 * CH2 ï¿½ CH2 ï¿½ C02 C2H5.
Since it does not form an addition product with bromine, reduction must have taken place in one of the nuclei only, and on account of the aromatic character of the compound it must be in that nucleus which does not contain the amino group. This tetrahydro compound yields adipic acid, (CH 2) 4 (CO 2 H) 2, when oxidized by potassium permanganate.
Recent limestones are being produced in this way and also in some places by the precipitation of calcium carbonate by sodium or ammonium carbonate which has been carried into the sea or formed by organisms. The precipitated carbonate may agglomerate on mineral or organic grains which serve as nuclei, or it may form a sheet of hard deposit on the bottom as occurs in the Red Sea, off Florida, and round many coral islands in the Pacific. Only the sand and the finest-grained sediments of the shore zone are carried outwards over the continental shelf by the tides or by the reaction-currents along the bottom set up by on-shore winds.
The manganese nodules afford the most ample proof of the prodigious period of time which has elapsed since the formation of the red clay began; the sharks' teeth and whales' ear-bones which serve as nuclei belong in some cases to extinct species or even to forms derived from those familiar in the fossils from the seas of the Tertiary period.
In most cases, however, little beyond the position and general appearance of the nuclei has been so far made known.
Certain individuals of a particular character form definite rounded cysts in the rectum of the fly; in this condition, the only sign of Trypanosome structure is afforded by the two nuclei, which remain separate.
This view has been fairly well supported by later discoveries; but, in addition to pyridine and quinoline nuclei, alkaloids derived from isoquinoline are known.
The very large single spores of Pertusaria have been shown to contain numerous nuclei and when they germinate develop a large number of germ tubes.
In these cases we should expect to find some reduced process of fertilization similar to that of Humaria granulata among the ordinary Ascomycetes, where in the absence of the antheridia the female nuclei fuse in pairs.
In other lichens we should expect to find the ascogenous hyphae arising directly from the vegetative hyphae as in Humaria rutilans among the ordinary fungi, where the process is associated with the fusion of vegetative nuclei.
g, g, Lemnisci, each with two giant nuclei.
Such hyphae may be multicellular, or they may consist of simple tubes with numerous nuclei and no septa (Phycomycetes), and are then non-cellular.
The cells of fungi, in addition to protoplasm, nuclei and sap-vacuoles, like other vegetable cells, contain formed and amorphous bodies of various kinds.
Although many fungi have been regarded as devoid of nuclei, and all have not as yet been proved to contain them, the numerous investigations of recent years have revealed them in the cells of all forms thoroughly examined, and we are justified in concluding that the nucleus is as essential to the cell of a fungus as to that of other organisms. The hyphae of many contain numerous, even hundreds of nuclei (Phycomycetes); those of others have several (Aspergillus) in each segment, or only two (Exoascus) or one (Erysiphe) in each cell.
As with other plants, so in fungi the essential process of fertilization consists in the fusion of two nuclei, but owing to the absence of well-marked sexual organs from many fungi, a peculiar interest attaches to certain nuclear fusions in the vegetative cells or in young spores of many forms. Thus in Ustilagineae the chlamydospores, and in Uredineae the teleutospores, each contain two nuclei when young, which fuse as the spores mature.
In young asci a similar fusion of two nuclei occurs, and also in basidia, in each case the nucleus of the ascus or of the basidium resulting from the fusion subsequently giving rise by division to the nuclei of the ascospores and basidiospores respectively.
Each "conidium" contains numerous nuclei and is really a zoosporangium, as after dispersal it breaks up into a number of zoospores.
In Cystopus Bliti the oosphere contains numerous nuclei, and all the male nuclei from the antheridium pass into it, the male and female nuclei then fusing in pairs.
The segments of the hyphae in this group usually contain several nuclei.
At the time of sporangial formation the protoplasm with numerous nuclei streams into the swollen end of the sporangiophore and there becomes cut off by a cell-wall to form the sporangium.
The cytology of these forms is very little known; Dangeard states that there is a fusion of two nuclei in the chlamydospore, but this requires confirmation.
In the development of the ascus we find two nuclei at the base which fuse together to form the single nucleus of the young ascus.
The single nucleus divides by three successive divisions to form eight nuclei lying free in the protoplasm of the ascus.
In some cases nuclear division is carried further before spore-formation occurs, and the number of spores is then 16, 32 and 64, &c.; in a few cases the number of spores is less than eight by abortion of some of the eight nuclei.
In some forms we find definite male and female sexual organs (Sphaerotheca, Pyronema, &c.), in others the antheridium is abortive or absent, but the ascogonium (oogonium) is still present and the female nuclei fuse in pairs (Lachnea stercorea, Humaria granulata, Ascobolus furfuraceus); while in other forms ascogonium and antheridium are both absent and fusion occurs between vegetative nuclei (Humaria rutilans, and probably the majority of other forms).
9) we have a true sexual process, while in the second and third cases we have a reduced sexual process in which the fusion of other nuclei has replaced the fusion of the normal male and female nuclei.
It is to be noted that all the forms exhibit the fusion of nuclei in the ascus, so that those with the normal or reduced sexual process described above have two nuclear fusions in their lifehistory.
with the two nuclei (as) 4, Union of the nuclei.
These have often been mistaken for nuclei and have to be carefully distinguished by differential stains.
In the formation of spores the nucleus of the cell divides, the protoplasm collects round the nuclei to form the spores by free-cell formation; the protoplasm (epiplasm) not used in this process becomes disorganized.
A fusion of nuclei was originally described by Jansens and Leblanc, but it was observed neither by Wager nor Guillermond and is probably absent.
In Schizosaccharomyces and Zygosaccharomyces, however, we have a fusion of nuclei in connexion with the conjugation of cells which precedes sporangium-formation.
In connexion with this condition of reduction a fusion of nuclei has been observed in Humaria rutilans and is probably of frequent occurrence.
By this means the ascus cell is brought uppermost, and after the fusion of the two nuclei it develops enormously and produces the ascospores.
If there are two fusions one would expect two reductions, and Harper has suggested that the division of the nuclei into eight in the ascus, instead of into four spores as in most reduction processes, is associated with a double reduction process in the ascus.
There is apparently a reduced sexual process by the fusion of the ascogonial (female) nuclei in pairs.
Functional male and female organs have been shown to exist in Pyronema and Boudiera; in Lachnea stercorea both ascogonia and antheridia a are present, but the antheridium a1 is non-functional, the ascogonial _s- - (fema l e) nuclei fusing in pairs; /'y' this is also the case' in Humaria /;' h; granulate and Ascobolus furfurs -./ '"aceus, where the antheridium is _ / /, - entirely absent.
ascogonium and antheridium contain numerous nuclei; they are to be looked upon as gametangia in which there is no differentiation of gametes, and since they act as single gametes they are termed coenogametes.
It has lately been shown that there is a fusion of nuclei in connexion with ascus formation, so that there can be no doubt of the position of this extraordinary group of plants among the Ascomycetes.
This very large group of plants is characterized by the possession of a special type of conidiophore - the basidium, which gives its name to the group. The basidium is a unicellular or multicellular structure from which four basidiospores arise as outgrowths; it starts asa binucleate structure, but soon, like the ascus, becomes uninucleate by the fusion of the two nuclei.
The Basidiales are further characterized by the complete loss of normal sexuality, but at some time or other in the life-history there takes place an association of two nuclei in a cell; the two nuclei are derived from separate cells or possibly in some cases are sister nuclei of the same cell.
The two nuclei when once associated are termed" conjugate "nuclei, and they always divide at the same time, a half of each passing into each cell.
This nuclear association of equivalent nuclei apparently represents a reduced sexual process (like the fusion of female nuclei in Humaria granulate and of vegetative nuclei in H.
(After Ruhland.) A, Young basidium with the two primary nuclei.
B, After fusion of the two nuclei.
This group like the rest of the Basidiales exhibits an association of nuclei at some point in its life-history, but unlike the case of the Basidiomycetes the point of association in the Uredineae is very well defined in all those forms which st .:_ possess aecidiospores.
We find a 3 thus that in the eu and opsis forms the association of nuclei takes place at the base of the aecidium which produces the aecidiospores.
There we find an association of nuclei either by the fusion of two similar cells as described by Christmann or by the migration of the nucleus of a vegetative cell into a special cell of the aecidium.
Before the teleutospore reaches maturity the nuclei fuse, and the uninucleate condition Q C then continues again until aeci dium formation.
Whether B, Formation of the first sporethe association of nuclei in the mother-cell (sm), from the ordinary mycelium takes place basal cell (a) of one of the by the migration of a nucleus rows of spores.
from one cell to another or C, A further stage in which whether two daughter nuclei from sm l the first aecidiobecome conjugate in one cell, spore (a) and the intercalary is not yet clear.
They have never been found to cause in fection, and they have not the characters of conidia; the large size of their nuclei, the reduction of their cytoplasm and the absence of reserve material and their thin cell wall all point to their being male gametes.
Although in the forms without aecidia the two generations are not sharply marked off from one another, we may look up the generation with single nuclei in the cells as the gametophyte and that with conjugate nuclei as the sporophyte.
It must be clearly borne in mind that though the Basidiomycetes show no traces of differ entiated sexual organs yet, like the micro and lepto forms of the Uredineae, they still show (in the association of nuclei and later fusion of From Annals of Botany, by permission of the Clarendon Press.
nuclei in the basFIG.
Miss Nichols fi -ids that it occurs very soon after the germination of the spore in Cc sinus, but no fusion of cells or migration of nuclei was to be observed.
mycelium ircdospores otachY' ar Mycelium aecidi'spores teleutospores (young) - mycelium SporoNtyte with conjugate nuclei GametohyEe with single nuclei teleutospores ?(mature) 8a ?; sporida ?m celium erm $ fertile cells Y sp (abortaitviae) (of aecidium) fertilized cells (of aecidium) and bears the basidiospores.
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.
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.
This view is still maintained by those who differentiate two acts of fertilization within the embryo-sac, and regard that of the egg by the first male-cell, as the true or generative fertilization, and that of the polar nuclei by the second male gamete as a vegetative fertilization which gives a stimulus to development in correlation with the other.
The signification of the coalescence of the polar nuclei is not explained by these new facts, but it is noteworthy that the second male-cell is said to unite sometimes with the apical polar nucleus, the sister of the egg, before the union of this with the basal polar one.
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 full number is restored in the fusion of the male and female nuclei in the process of fertilization, and remains until the formation of the cells from which the spores are derived in the new generation.
Biologie der Algen, by permission of Gustav Fischer.) Dermatophyton grows on the carapace of the tortoise and Trichophilus nucleus, each cell is found to contain many small nuclei, and is in the hairs of the sloth.
The so-called zoospore of Vaucheria is a coenocyte covered over with paired cilia corresponding in position to nuclei lying below.
In coenocytic forms the zoospores would seem to arise simultaneously, probably because many nuclei are already present.
All investigation goes to show that an essential part of sexual union is the fusion of the two nuclei concerned.
It is interesting to know, on the authority of Oltmanns, that when the oosphere is forming in the oogonium of Vaucheria, there is a retrocession of all the included nuclei but one.
It would seem that in some cases the nuclei of the gametes remain distinct in the zygospore for a considerable time after conjugation.
It would seem that eight nuclei primarily arise in all Fucaceae, and that a number corresponding to the number of oospheres subsequently formed is reserved, the restbeing discharged to the periphery, where they may be detected at a late stage.
It is singular that in the last-named species two nuclei occur regularly in the spermatium.
In the latter case, and especially where the union is with a special auxiliary cell, it is of importance to know what happens to the nuclei of the fusing cells.
Schmitz was of opinion that in the cases of open union there occurred a fusion of nuclei similar to that which occurs in the sexual union of two cells.
Corallina sp., tetrasporangia with zonate arrangement of tetraauxiliary cells, the nuclei of which a and b retire to the wall.
(A, C, D, E, F, G, H, K, L, M, P, Q, from Oltmanns, by permission of Gustav Fischer; B, N, 0, R, from Engler and Prantl, by permission of Wilhelm Engelman,) mass and from it all the nuclei of the carpospores are thus derived.
As is well known, the dividing nuclei of the cells of the sporophyte generation of the higher plants exhibit a double number of chromosomes, while the dividing nuclei of the cells of the gametophyte generation exhibit the single number.
Starting from a widely diffused nebula, more or less uniform, we find that, in consequence of gravitational instability, it will tend to condense about a number of nuclei.
As the nuclei grow by the attraction of matter they begin to be capable of retaining the lighter gases, and atmospheres of hydrogen and helium are formed.
The most recent works (Vejdovsky, Mend), however, appear to show that nuclei of a structure and mode of division almost typical are to be found in some of the largest bacteria.
This product is largely derived from the nuclei of the leucocytes, which contain large quantities of the nucleo-proteids, of which uric acid is a decomposition product.
Evidence has lately been adduced of the existence of numerous nuclei in the pollen-tubes of the Araucarieae, and it seems probable that in this as in several other respects this family is distinguished from other members of the Coniferales.
Blackman, who also succeeded in showing that the nuclei of the sporophyte generation contain twice as many chromosomes as the nuclei of the gametophyte.
Other observers have in recent years demonstrated a similar relation in other genera between the number of chromosomes in the nuclei of the two generations.
Cupressineae) or separated from one another by a few cells of the prothallus, each ovum being immediately surrounded by a layer of cells distinguished by their granular contents and large nuclei.
In the process of fertilization the two male generative nuclei, accompanied by the pollen-tube nucleus and that of the stalk-cell, pass through an open pit at the apex of the pollen-tube into the protoplasm of the ovum.
After fertilization the nucleus of the egg divides, the first stages of karyokinesis being apparent even before complete fusion of the male and female nuclei has occurred.
The result of this is the production of four nuclei, which eventually take up a position at the bottom of the ovum and become separated from one another by vertical cellwalls; these nuclei divide again, and finally three tiers of cells are produced, four in each tier.
In certain species of Gnetum described by Karsten the megaspore contains a peripheral layer of protoplasm, in which scattered nuclei represent the female reproductive cells; in Gnetum Gnemon a similar state of things exists in the upper half of the megaspore, while the lower half agrees with the megaspore of Welwitschia in being full of prothallus-tissue, which serves merely as a reservoir of food.
In Gnetum Gnemon, as described by Lotsy, a mature embryo-sac contains in the upper part a large central vacuole and a peripheral layer of protoplasm, including several nuclei, which take the place of the archegonia of Ephedra; the lower part of the embryo-sac, separated from the upper by a constriction, is full of parenchyma.
17, B and C, pt); finally the two generative nuclei pass out of the tube and fuse with two of the nuclei in the fertile half of the megaspore.
The nuclei of the cells of the sexual generation possess a definite number of chromosomes and this number is also characteristic of the sexual cells.
The megaspore becomes filled with the female prothallus, the formation of cell-walls commencing at the pointed end of the spore, where from the first the nuclei are more numerous, and later extending to the base.
All the bishops in a coenobium were subject to the abbot; but besides the bishop in the monastic families, every tuath or tribe had its own bishop. The church in Ireland having been evolved out of the monastic nuclei already described the tribe bishop was an episcopal development of a somewhat later period.
For purposes of defence early settlers naturally chose elevated ground, frequently a hill with precipitous sides, and these early citadels became in many parts of the world the nuclei of large cities which grew up on the surrounding lower ground.
9): (I) a vesicular portion (s) opening to the exterior on the ventral surface of the legs by a narrow passage (s.d); (2) a coiled portion, which is again subdivided into several sections (s.c); (3) a section with closely-packed nuclei ending by a somewhat enlarged opening (p.f); (4) the terminal portion, which consists of a thin-walled vesicle.
The segmentation is peculiar, and leads to the formation of a solid gastrula, consisting of a cortex of ectoderm nuclei surrounding a central endodermal mass, which is exposed at one point - the blastopore.
The endoplasm is ramified between alveoli; it contains a large nucleus (in Polykrikos there are eight nuclei, accompanied by smaller, more numerous bodies regarded by O.
' Gloioconis, found by Renault in a coprolite of Permian age, was regarded by him as a Cyanophycean allied to Gloeocapsa; this may be so, but the argument drawn from the absence of nuclei, considering the extreme rarity of recognizable nuclei even in the best preserved fossil tissues, can hardly be taken seriously.
accrete X-rays, accreting black holes in their nuclei can be identified which would be very difficult to find in any other way.
adiabatic nuclei approximation.
After analyzing individual transformants, nucleoplasmin was shown to successfully target aequorin to nuclei.
amygdaloid nuclei (3 ).
only atomic nuclei with an odd number of neutrons, such as 1 H and 13 C can be detected with NMR.
Variety of vacuum giesel becquerel then a professor nuclei produced by x-rays.
brainstem nuclei, which in turn affects RSA.
collide with other nuclei, causing them in turn to split, releasing further neutrons.
condensation nuclei, which are generally atmospheric pollutants, natural or man-made.
Greater ionizing radiation from the Sun during those times also tends to produce more nuclei in the atmosphere for cloud condensation.
In all cases tumor cells were relatively small and showed monomorphic or pleomorphic nuclei, prominent nucleoli, and ill-defined cytoplasm.
H Be able to attribute this decrease in activity to a corresponding decrease in the number of unstable nuclei.
deformed nuclei can rotate ever more faster to produce a collective spin.
A powerful electromagnet causes the nuclei of atoms (particularly hydrogen in water molecules) to align magnetically.
Enhanced deposition of radon daughter nuclei in the vicinity of power frequency electromagnetic fields.
explosive device deriving its power from fission or fusion of nuclei or from both.
Several neutrons are also produced which may go on to strike the nuclei of other atoms causing further fission.
Infection also involves motor cortex, hypothalamus, and globus pallidus, brainstem nuclei, reticular formation, cerebellar roof nuclei, and vermis.
Basically, the Hydrogen nuclei fuse together in a series of reactions to form Helium nuclei and energy.
If sufficiently energetic, the created hadrons can undergo further interactions, making yet new hadrons and disrupting more nuclei.
haploid nuclei, which migrate to the tips of the basidia.
interphase nuclei on intact 6 mu m tissue sections.
Due to their narrow spectral lines, they also act as a high-resolution probe of gas kinematics in outflow regions and active galactic nuclei.
metastable explosion products decay more slowly by sequential evaporation of light nuclei.
In contrast, the DNA in somatic nuclei is not fully neutralized by histones.
Early in 1932 James Chadwick discovered the neutron, a particle in the nuclei of most atoms.
nucleusscopically, or classically, deformed nuclei can rotate ever more faster to produce a collective spin.
nucleusost prominent modulatory input that CN neurons receive originates from serotoninergic neurons of raphe nuclei.
nucleusby their optical properties, their efficiency to act as condensation nuclei and their lifetime with respect to deposition processes can be affected.
nucleusopy number of chromosomes 7 and 17 was determined in interphase nuclei on intact 6 mu m tissue sections.
nucleus20 he speculated that hydrogen nuclei were a building block of all nuclei.
nucleus reasonably dark skies, a small telescope will show the nuclei of the two galaxies separated by 4.5 minutes of arc.
The paraventricular nuclei produce mostly oxytocin and the supraoptic mostly vasopressin although both hormones may also be produced by the other type of nuclei.
The nuclei of the cells show pleomorphism, with variation in size, shape and chromatin staining pattern.
In the action the Alabama polytechnic produce nuclei for the same sort.
raphe nuclei and the locus ceruleus.
redshift galaxies and active galactic nuclei.
The high kinetic energies are needed to overcome the repulsion of the two positive nuclei.
reticular formation or lateral thalamic nuclei were seen in 17% (2) of those studied.
He uses high-resolution solid-state detectors to make precision measurements on the gamma rays emitted by radioactive nuclei.
What is the nature of the massive dusty torus believed to surround Active Galactic Nuclei?
Tetanus has been reported to induce lesions in the vagal nuclei, while locally applied toxin may lead to excessive vagal nuclei, while locally applied toxin may lead to excessive vagal activity.
The body is covered externally by a chitinous cuticle which is a product of the subjacent epidermic layer in which no cell limits can be detected though nuclei are scattered through it.
The relation of the nucleolus to the chromosomes is clearly seen in the reconstruction of the daughter nuclei after division in the cells of the root-apex of Phaseolus (fig.
The outer protective walls of the oospores of some Fungi are formed out of protoplasm containing numerous nuclei, which is at an early stage separ~t~d from tl-,c. r,rofc,nI,,,zm of ih,~ o,~nor~ T,.
fusion of two germ nuclei.
sma in amoun a B, Union of the vermiform nuclei cell consists mainly of a with the egg-nucleus and the two nucleus.
Even in the multinucleate oosphere of Albugo bliti the nuclei fuse in pairs; and in the oospheres of Sp/zaero plea, which may contain more than one nucleus, the egg nucleus is formed by the fusion of one only of these with the spermatozoid nucleus (Klebahn).
In nearly all cases the nuclei appear to fuse in the resting stage (fig.
In other cases the two nuclei place themselves side by side, the nuclear membrane between them disappears, and the contents fuse togethernuclear thread with nuclear thread, and nucleolus with nucleolusso completely that the separate constituents of the nuclei are not visible.
During the process of fertilization in the Angiosperms it has been shown by the researches of Nawaschin and Guignard that in Lilium and Fritillaria both generative nuclei enter the embryo sac, one fusing with the oosphere nucleus, the other with the polar nuclei (fig.
Both nuclei are elongated vermiform structures, and as they enter the embryo sac present a twisted appearance like a spermatozoid without cilia (fig.
7) the nuclei possess all the structures found in the higher plants, nuclear membrane chromatin network and nucleolus (fig.
The only groups of plants in which typical nuclei have not been found are the Cyanophyceae, Bacteria and Yeast Fungi.
But the recovery of successive historical nuclei does not furnish a continuous thread, and if one is to be guided by the historical context of events the true background to each nucleus must be sought.
But it must be here understood that each member of these condensed nuclei need not necessarily be identical in structure; thus the central nuclei in anthracene and phenanthrene differ very considerably from the terminal nuclei (see below, Condensed Nuclei).
The syncytium is traversed by a series of branching tubules containing fluid and is controlled by a few wandering, amoeboid nuclei (fig.
The cytoplasm of the cell now undergoes division in a line between the two daughter nuclei.
In the same way, by electrolysing a mixture of a metallic salt and an ester, other nuclei may be condensed; thus potassium acetate and potassium ethyl succinate yield CH 3 * CH2 Ã¯¿½ CH2 Ã¯¿½ C02 C2H5.
Here then we have the basis of a view in which there are not two media to be considered, but one medium, homogeneous in essence and differentiated as regards its parts only by the presence of nuclei of intrinsic strain or motion - in which the physical activities of matter are identified with those arising from the atmospheres of modified aether which thus belong to its atoms. As regards laws of general physical interactions, the atom is fully represented by the constitution of this atmosphere, and its nucleus may be left out of our discussions; but in the problems of biology great tracts of invariable correlations have to be dealt with, which seem hopelessly more complex than any known or humanly possible physical scheme.
It appears to conform more or less to the radial or rosette type of multiplication, enlarged rounded parasites, with a varying number of nuclei (up to about eight) uniformly arranged near the periphery, having been often noticed (fig.
As a rule the nuclei of the mycelium are very minute (1.5-2 µ in Phycomyces), but those of many asci and spores are large and easily rendered visible.
The fate of these nuclei is doubtful, probably they fuse in pairs (fig.
ascogonium and antheridium contain a number of nuclei (i.e.
Then two successive nuclear divisions occur resulting in the formation of four nuclei which later migrate respectively into the four basidiospores (fig.
After this association the nuclei continue in the conjugate condition so s that the aecidiospores, the uredospore-bearing mycelium, the uredospores and the young teleutospores all contain two paired nuclei in their cells (fig.
idium), a reduced fertilization which denotes their derivation, through the Uredineae, from more typically sexual forms. No one has yet t.-ade out in any form the exact way in which the association of nuclei tr -.-es place in the group. The mycelium is always found to contain conjugate nuclei before the formation of basidia, but the point at which the conjugate condition arises seems very variable.
a fusion of two benzene nuclei, the hydrogen atoms being numbered as in the inset / 8 1 formula 7(I/12; 1, 4, 5, 8 are a-positions, 2, 3, 6, 7 are 6 // 3 4 1 -5 or 4-8 5 diderivatives are ana, whilst 1-8 or 4-5 are peri (see Chemistry, Organic).
Jeans has even estimated theoretically the average distances apart of these nuclei, and has shown that it agrees in order of magnitude with the observed distances of the stars from one another (Astrophysical Journal, vol.
As the result of fertilization, the fertilized nuclei of the megaspore become surrounded by a cell-wall, and constitute zygotes, which may attach themselves either to the wall of the megaspore or to the end of a pollen-tube (fig.
I have also done some notable research on active galaxies and searches for high redshift galaxies and active galactic nuclei.
Gray matter lesions in the reticular formation or lateral thalamic nuclei were seen in 17% (2) of those studied.
Most of these high energy nuclei are thought to be hurled at us by supernova shock fronts, perhaps from collisions with dust grains.
Tetanus has been reported to induce lesions in the vagal nuclei, while locally applied toxin may lead to excessive vagal activity.
Ossification (the process whereby tissue becomes bone) of most bony nuclei of the long bones and round bones does not complete until after birth.
The subthalamic nucleus sends signals to the globus pallidus, which in turn blocks the thalamic nuclei.
Finally, the thalamic nuclei send signals to the motor cortex.
It seems to be fairly well established that in the meiotic phase there is a truequalitative division brought about by the pairing of the chromosomes during synapsis, and the subsequent separation of whole chromosomes to the daughter nuclei.
In all cases of polar nuclei.
A, Basidium with two nuclei.
B, single nucleus due to th~ fusion of the two pre-existing nuclei.
F, Separation of the chromosomes into two groups G, Chromosomes grouped at opposite ends of the spindle to forn the daughter nuclei.
A protoplasinic lining is found on their walls which contains nuclei.
Carbocyclic rings will next be treated, benzene and its allies in some detail; and finally the heterocyclic nuclei.
Cyclic Hydrocarbons and Nuclei.
The next members are the -isomers anthracene and phenanthrene, C14H,0, formed from three benzene nuclei.
The skeletons of these types are (the carbon atoms are omitted for brevity): We have previously referred to the condensation of heterocyclic ring systems containing two vicinal carbon atoms with benzene, naphthalene and other nuclei.
The more important nuclei of this type have received special and non-systematic names; when this is not the case, such terms as phen-, benzo-, naphthoare prefixed to the name of the heterocyclic ring.
One or two benzene nuclei may suffer condensation with the furfurane, thiophene and pyrrol rings, the common carbon atoms being vicinal to the hetero-atom.
a-pyrone condenses with the benzene ring to form coumarin and isocoumarin; benzo-'y-pyrone constitutes the nucleus of several vegetable colouring matters (chrysin, fisetin, quercetin, &c., which are derivatives of flavone or phenyl benzo-y-pyrone); dibenzo--ypyrone is known as xanthone; related to this substance are fluorane (and fluorescein), fluorone, fluorime, pyronine, &c. The pyridine ring condenses with the benzene ring to form quinoline and isoquinoline; acridine and phenanthridine are dibenzo-pyridines; naphthalene gives rise to a-and /3-naphthoquinolines and the anthrapyridines; anthracene gives anthraquinoline; while two pyridine nuclei connected by an intermediate benzene nucleus give the phenanthrolines.
Naphthyridines and naphthinolines result from the condensation of two pryridine and two quinoline nuclei respectively; and quino-quinolines are unsymmetrical naphthyridine nuclei condensed with a benzene nucleus.
The same increase accompanies the introduction of the amino group into aromatic nuclei.
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