Nucleolar Material Research Articles

The Morphology of the Chromosomes of <i>Pisum sativum</i>

1. Different methods of fixing root tips and Pollen mother cell smears of peas are described and discussed.2. Formalin appears to render some of the nucleolar material and the matrix substance of somatic and meiotic chromosomes soluble in water, or to fail to render them insoluble as do chromic-fatty acid-formalin fixatives.3. Alcohol appears to dissolve the meiotic chromosome matrix or to render it achromatic.4. An intimate relationship between, and possible identity of nucleolar material and the matrix substance of somatic chromosomes is established.5. The metotic and meiotic ehromosomes are described. The characters of each of the seven 'pairs permit identification of the individual members of the complement. They are as follows:6. The chromonemata of the first meiotic metaphase and the chromosomes of later stages are found to show the Same individual characteristics as the somatic chromosomes.

Nucleoli of the Root Tip and cambium of <i>Pinus Strobus</i>

1. The root tip and cambium of Pinus Strobus were fixed in several different fluids so as to preserve the chromatin, plastin, and mitochondria in the following combinations:-(1) chromatin, plastin, and mitochondria fixed; (2) plastin and mitochondria fixed and chromatin dissolved; (3) chromatin and plastin fixed, mitochondria dissolved; (4) plastin fixed, mitochondria dissolved, chromatin rendered unstainable; (5) chromatin fixed, mitochondria dissolved, plastin ren-dered unstainable. It was thus possible to separate the plastin from the chromatin, chemically, and to follow it through the several mitotic phases unobscured by any other nuclear constituent. It was also possible to distinguish any possible granules of plastin in the cytoplasm from the mitochondria.2. The organization of nucleolar material in both the resting and dividing nucleus of Pinus differs in many important details from that recently described in a number of angiosperms. The resting nucleus of Pinus contains an average of six nucleoli which are in intimate contact with the chromatin threads of the reticulum. On the initiation of karyokinesis, each nucleolus becomes attached to the spireme. The plastin passes into the spireme and is distributed to the daughter cells as a part of the chromosomes. On the reorganization of the daughter nuclei, the plastin is consolidated into the typical nucleoli of the resting cell. Unlike Zea, the Pinus nucleoli do not persist to metaphase, and diserete globules of plastin do not, pass from the equatorial plane to the poles of the spindle. No evidence was found of any fragments of nucleolar material passing out into the cytoplasm.3. Two distinct substances can be observed in the resting nucleoli in living cells. As these substances have a different index of refrac-tion, the nucleoli appear vacuolate. These substances can be separated by fixation in the resting nucleus and in the later telophases. During the other mitotic phases, however, they have not been separated, so that, at present, it is not possible to trace each one individually through the entire cycle of cell division. Neither substance is chromatin.4. The bearing of the activity of plastin during mitosis upon several theories concerning the forces involved in cell division is dis-cussed.The author wishes to express his obligation to Professor I. W. BAILEY for his assistance throughout the course of this investigation and especially for his help in preparing the cambium for cytological investigation. Professor BAILEY's preparation of living cambial tissue made it possible to check the several fixation images wich the struc-tures of untreated cells. The author also wishes to thank Miss ANNA F. FAULL for drawings in Plate 6 and the Text-Figure.

Certain Phenomena of Tenthredinid Oogenesis as revealed mainly by Feulgen’s Nuclear-Reaction

ABSTRACT By the use of Feulgen’s ‘nuclealreaktion’ certain points of Tenthredinid oogenesis have been subjected to closer study. The chromatin of the early nurse-cells of Allantus pallipes exists in the form of granules, the majority of which occur close to the nuclear membrane. In the older cells a nuclear network appears in which is distributed granules of chromatin. In Thrinax mixta, where the ovarioles were more highly developed, the chromatin of the nurse-cells occurs as granules scattered through the nucleus ; a nuclear network is not present, but certain granules appear to be connected by a thread. The granules which were shown to surround the nurse-cell nuclei (in material treated by Bensley’s method and also by fixation in Bouin’s picro-formol and subsequently stained in iron haematoxylin) and which were formerly regarded as chromatin emissions from the nurse-cell nuclei (9) were not revealed by Feulgen’s technique. They therefore cannot be regarded as chromatin. Their precise nature and origin remains undetermined. The nucleoli of the early nurse-cells of both species, as revealed by Mann’s methyl-blue eosin, are faintly basophil. Later they break up into a number of basophil bodies which undergo fragmentation ; formerly (technique and reference as in 1) the basophil nucleolus and the basophil bodies originating from it were termed ‘nuclear material’ undergoing fragmentation. While this basophil nucleolar material presents a fragmented appearance, it increases in amount as evidenced by the large number of basophil bodies present in the older nurse-cell nuclei. This material is utilized for the nourishment of the egg after the latter engulfs the nurse-cell nuclei. Nucleolar extrusions to the cytoplasm do not occur. The behaviour of the chromatin of the follicle-cell nuclei is similar to that of the nurse-cell nuclei except that in Allantus pallipes the nuclear chromatin network as demonstrated by Feulgen’s technique disappears in the older cells. The nucleoli of the follicle-cells are basophil. They become broken up in the older cells, but in most cases the resulting masses remain in contact. Nucleolar extrusions to the cytoplasm do not occur. The occurrence of deeply basophil material in the cytoplasm of the follicle-cells of Thrinax mixta stained with Mann’s methyl-blue eosin, formerly described for Bonin fixed material stained in iron haematoxylin (9), suggests that some substance in solution may be passed into the ooplasm ; extrusion of granules from the follicle-cells to the ooplasm does not take place. The absence or non-visibility of chromatin (Feulgen’s technique) from the oocytes of Thrinax mixta, and its disappearance from the older oocytes of Allantus pallipes, would indicate that the chromatin undergoes a chemical change during oogenesis such as suggested by Koch for Chilopods. The oxyphil and basophil nucleoli of the oocytes do not react to Feulgen’s technique for chromatin ; this agrees with Ludford’s findings for the mouse and forLimnaeastagnalis.

Growth and maturation in the parthenogenetic and sexual eggs of Moina macrocopa

AbstractFrom a study of over 1000 mothers, the female chromosome number appears to be 2N = 22; N = 11. The male number has not been exactly determined, but is presumably not haploid. Only one maturation division occurs in the parthenogenetic egg, and the authors have seen only one in the sexual egg. During the growth stages of the eggs, the chromatin is totally obscured by a large amount of deeply staining nucleolar material which exhibits several phases. Ultimately, this material is apparently absorbed into the ooplasm. Just before the egg is laid, the ovoid chromosomes, in late prophase or in metaphase, are seen in a germinal vesicle situated always at one side of the egg. The maturation division occurs immediately after egg laying. A degenerate body, hitherto undescribed, is noted in the ripe parthenogenetic egg, situated at the pole opposite the germinal vesicle. It is believed to arise by reorganization of nucleolar substance. The body in the sexual egg desribed by Weismann and Ishikawa ('91) as the Paracopulationzelle is noted and its interpretation by these authors questioned, but, for lack of sufficient evidence, no counter‐explanation is offered. The possible relation between experimental sex control and the time of maturation division in the parathenogenetic egg is discussed.

Nucleolus in Root Tip Mitosis in Zea mays

By the use of different fixatives it was found possible to fix: (1) chromatin, plastin, and mitochondria; (2) chromatin, plastin, and dissolve all mitochondria; (3) plastin and mitochondria, and dissolve the chromatin; (4) chromatin, and dissolve or render unstainable all plastin and mitochondria; and (5) plastin, and dissolve all chromatin and mitochondria. It was thus possible to investigate the behavior of the nucleolar material during cell division unobscured by any chromatin or mitochondria. In the resting nucleus all chromatin is localized in the reticulum, the nucleolus containing none. After the spireme is formed the nucleolus becomes connected with it, and later becomes pear-shaped, the point of attachment being at the smaller lobe of the pear. As the spireme flattens out on the equatorial plane nucleolar material flows into it. The smaller lobe of the nucleolus is drawn out and splits in two, giving the nucleolus two connections with the spireme. As the nucleolus loses material it becomes rod-sh...

ORIGIN OF THE MESODERM AND BEHAVIOR OF THE NUCLEOLUS IN REGENERATION INLUMBRICULUS

Nuclei and Nucleoli in Uninjured Individuals.1. The nuclei and nucleoli of the hypodermal cells are small except in the growing tail region. Here they are enlarged, especially in the cells on the ventral side which are involved in the formation of the new nerve cord.2. Large nucleoli are present in the cells of the setigerous glands near the growing region of the tail. In old segments they are small.3. The gut nucleoli are small in the first twelve segments. They are larger from this region up to twenty or thirty segments from the posterior end. In these segments, they are again small.4. Double nucleoli are occasionally found in the mid-gut, where large nucleoli are present.Origin of New Tissue in Regeneration.5. Double nucleoli and mitoses are found in the intestine for eleven or twelve segments from the wound. In this same region the nucleoli are considerably enlarged.6. Cell proliferation in the old intestine practically ceases between the sixth and seventh days of regeneration.7. Neoblasts metamorphose and migrate to the wound at the anterior end as well as at the posterior end. At least eight or nine segments furnish these cells, the four or five nearest the wound apparently playing the most important part as observed by Krecker.8. The failure of the muscle and nerve cells of the old part to form the corresponding new structures in regeneration is perhaps due to the fact that the cytoplasm of these cells has become highly modified, thus rendering them less susceptible to activation.9. The spindle-shaped cells in the dorsal portion of the bud cavity at the anterior end are derived from the hypodermis and not from the muscles of the old part.10. In both anterior and posterior regeneration the nuclei and nucleoli increase in size in the ectoderm cells in the immediate vicinity of the wound. This enlargement is no more rapid in one part than in another; it continues longer in the ventral cells so that by the second day it is greater there.11. The metamorphosis of the ectoderm is not in all probability due to the proximity of the neoblasts, as supposed by Krecker, but instead to an independent transformation.12. The cells of the setigerous glands in the new bud have large nuclei and nucleoli.13. A feature common to all the cells which take part in the formation of the tissues in the regenerating bud is the presence of large nuclei and nucleoli.14. The amount of nucleolar material present in a cell seems to be an index of the activity of its nucleus both in cell-metabolism and in preparation for cell division.15. In Lumbriculus there is no evidence of any division or even of a clearly defined constriction in any of the nuclei of the gut which contain two nucleoli.16. The presence of two nucleoli in a single nucleus is not a step in amitosis, as many have supposed, but is due to the increase in nucleolar substance beyond the amount which can exist within that particular nucleus as a single droplet.17. The various tissues seem to be derived in the same manner both in anterior and in posterior regeneration.

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The Development of the Mole (Talpa Europea), the Ovarian Ovum, and Segmentation of the Ovum

The membranes surrounding the ripe ovarian, ovum are two: (1) a single outer, thick, zona radiata, with a granular peripheral and a transparent inner portion, pierced radially by fine canals through which nutriment is obtained by the ovum from, the follicular cells (of the discus proligerus) immediately in contact with the zona: (2) an inner very delicate vitelline membrane which closely covers the ovum itself; and between these membranes is a space, the circum-vitelline space. The confirmation of Reichert's (No. 18), Meyer's (No. 17), and van Beneden's (No. 4) observations as to the presence of the inner delicate vitelline membrane appears of some interest as many embryologists are still sceptical of its existence, while the relation of the follicular cells with the radial canals of the zona supports the view as to the source of the nutriment of the ovarian ovum. On the other hand the fact that nothing was seen comparable to a micropyle in the zona, such as M. Barry (No. 3), and Meissner (No. 16), described, nor any follicular cells within the zona such as Lindgren (No. 15), von Sehlen (No. 21), and Virchow (No. 22), have observed, is some further proof that the conditions of the material investigated by these authors was abnormal. The yolk contained within the ovum, which is of two kinds: viz. (1) homogeneous vesicular bodies, (2) minute highly refractile granules, is contained within the meshes of a protoplasmic reticulum; it is dense and contains no large globules such as Beneden (Nos. 6 and 7) describes in theBat's ova. The rounded or oval nucleus contains a single centrally placed nucleolus and a variable number of smaller or larger granules, which may possibly be considered as nucleolar material. During maturation the vitellus becomes divided into a medullary granular, and a cortical non-granular portion, the circum-vitelline space between the zona radiata and the vitelline membrane is enlarged, while the vitellus itself contracts away from the vitelline membrane excepting (1) here and there where pseudopodia-like processes connect the two, and (2) at one spot where the polar bodies are formed. At this latter place two polar bodies may be seen in the specimen figured, outside the vitelline membrane, whilst the nucleus remains as the female pronucleus lying in the peripheral portion of the ovum. Finally, the vitellus again expands and the nucleus retires to the centre of the ovum and is no longer to be seen. Assuming that these observations are correct, Beneden's description of the ejection of the vesicle to form the polar bodies and the subsequent non-nucleated condition of the ovum must be considered erroneous. Impregnation appears to be effected by a single spermatazoon, although a considerable number of spermatazoa find their way through the zona and may be seen lying passively in the circumvitelline space. The segmentation occurs while the ovum travels down the Fallopian tube. Two and then four segments are formed, after which the course of segmentation is irregular. The segments themselves are of irregular size and do not appear to be divisible into two kinds (epiblastic and hypoblastic) as Beneden describes. After its entrance into the uterus, a division of the segments into an outer hyaline layer and inner deeply granular mass takes place, and I would suggest the hypothesis that the vitelline matter which was originally contained in all segments alike has been transmitted from the outer segments to the segments lying in the interior of the ovum, in order that the former segments may the more readily and actively multiply and flatten out to form the wall of the blastodermic vesicle. The epiblast of the vesicle and of the embryo is derived from the whole of the outer layer and by far the largest proportion of the inner mass of segments. The hypoblast is derived from the small remaining portion of the inner mass and the mesablast, subsequently, from both epiblast and hypoblast layers. This being the case, the division of the segmentation spheres, by Beneden, into epiblast and hypoblast spheres from the time when the first two segments were formed, is incorrect; and at the same time the theory of a comparison of the metagastrula stage with the gastrula of other animals is likewise untenable.