A growth curve of cell numbers in the neural retina of embryonic chicks

The growth of cell numbers in a normal embryonic population of neural retinal cells is described. The numbers were estimated from a time shortly after the neural retina first becomes recognizable to a time when numbers of retinal cells have become steady. Cell numbers were estimated in preparations of an entire neural retina dispersed into a suspension of single nuclei which were then counted in a Coulter counter. The growth curve of the ln numbers of cells has three phases of growth: an exponential phase during which there is steady-state exponential growth, a differentiative phase during which cell proliferation ceases and an end phase when no further change in cell numbers can be detected. The variances of the ln numbers of cells were highest during the exponential phase. The variances decreased during the differentiative phase and were at their lowest during the end phase. For variances to decrease requires mechanisms which control the final numbers of cells in the neural retina very precisely. The implications of mechanisms which operate by controlling cell lineages are explored.     

A Growth Curve of Cell Numbers In the Neural Retina of Embryonic Chicks

ABSTRACT The growth of cell numbers in a normal embryonic population of ncural retinal cells is described. the numbers were estimated from a time shortly after the neural retina first becomes recognizable to a time when numbers of retinal cells have become steady. Cell numbers were estimated in preparations of an entire neural retina dispersed into a suspension of single nuclei which were then counted in a Coulter counter. the growth curve of the In numbers of cells has three phases of growth: an exponential phase during which there is steady-state exponential growth, a differentiative phase during which cell proliferation ceases and an end phase when no further change in cell numbers can be detected. the variances of the In numbers of cells were highest during the exponential phase. the variances decreased during the differentiative phase and were at their lowest during the end phase. For variances to decrease requires mechanisms which control the final numbers of cells in the neural retina very precisely. the implications of mechanisms which operate by controlling cell lineages are explored.     

Chromosome numbers and taxonomy in Cryptocoryne (Araceae). II

Chromosome numbers for 38 species of Cryptocoryne are reported, 16 of which have not been reported earlier. About 90% of the species of Cryptocoryne have now been investigated cytologically. On the basis of chromosome numbers, morphology, and distribution, it is possible to distinguish some 24 groups within the species investigated. The chromosome numbers represent a heteroploid series which is based on the (secondary) base numbers 10, 11, 14, 15, 17, and 18. Evidence is given that 2n = 36 is the more primitive one. Evolution on the chromosome level has most likely gone in the direction of a reduction in numbers. Two new species, Cryptocoryne amicorum De Wit & N. Jacobsen and C. keei N. Jacobsen, are described.     

中国蕨类植物细胞分类学研究概况

中国蕨类植物类群十分丰富,由63科230属约2600种组成,其中约有10％的种类为中国特有。迄今为止,中国蕨类植物进行过染色体计数的种类约有395种,仅占中国蕨类植物总数的15％,其中48％为多倍体。本文对中国蕨类植物细胞分类学研究的历史和现状进行了综合评述。文中论述了蕨类植物染色体数目和染色体基数在系统学上的应用以及蕨类植物染色体组型分析、多倍化、无融合生殖、多倍体复合体及网状进化的研究概况。中国20多年的蕨类植物细胞分类学研究表明,蕨类植物的染色体数目、基数、组型分析、多倍化及其繁殖方式对蕨类植物的分类、起源和演化的研究都有重要作用,对种及种复合体的鉴定、科属的划分也有重要的参考价值。并对中国蕨类植物细胞分类学研究提出了一些建议。     

A Report on the Chromosome Numbers of Chinese Umbelliferae

Chromosome numbers are reported for 26 species and varieties of Umbelliferae which belong to 3 subfamilies and 19 genera in this paper. Of these, 13 counts are new records and some problems about chromosome numbers of Umbelliferae are simplydiscussed.     

A report on the chromosome numbers of Chinese Umbelliferae

Chromosome numbers are reported for 26 species and varieties of Umbelliferae which belong to 3 subfamilies and 19 genera in this paper. Of these, 13 counts are new records and some problems about chromosome numbers of Umbelliferae are simplydiscussed.     

A Report on Chromosome Numbers of Chinese Umbelliferae

This is the third report of chromosome numbers of Umbelliferae after 1981 and 1985, which deals with 24 species and varieties of 15 genera including 2 endemic genera and 10 endemic species, and most of them are distributed in southwestern China. Of them, 18 counts are newly reported. The taxonomic significance is discussed in relation with their basic numbers, translocation heterozygote and polyploids. It is considered that polyploids are wide-spread in Hydrocotyle L. 4, 6, 7, 8 are the basic numbers of Bupleurum L. which provides the cytological evidence for further study on their evolutionary process. n=9 and 10 occurrespectively in two different sections of Pimpinella L. and their basic numbers may be used for classification at the section level. The ring formation of four chromosomes at diakinesis of Heracleum henryi Wolff reveals that translocation heterozygotes is one of the factors in specific differentiation of Umbelliferae.     

A mathematical model for the temporal pattern of a population structure,with particular reference to the flour beetle

Equations are derived to represent the time course of the population numbers of the various stages of the flour beetle. The assumption of constant duration of the life stages and the absence of delayed effects leads to equations from which the various population numbers can be calculated in terms of the parameters of the system. Formulae are given for the estimation of many of the latter from observations on population numbers. Calculations show that the principal features of the observed changes in population structure can be accounted for on the basis of a simple model in which it is further assumed that each interaction is proportional to the product of the numbers of the two given interacting stages. A more detailed analysis may require secondary interaction coefficients. Suggestions for estimation of such coefficients are given.     

Oscillation in the number of bacteria during starvation]

Factors stimulating the increase in the numbers of Escherichia coli bacteria and accelerating their death were studied. It was shown that oscillations in the numbers of viable bacteria are due to periodic changes in the activity of these two factors, which do not coincide in phase. The oscillations in cell numbers occur only at particular cell concentrations.     

Ideal phyllotaxis on general surfaces of revolution

A mathematical model is presented for botanical features growing at an arbitrary rate on an arbitrary surface of revolution. At each point on the surface a lattice is defined, describing the phyllotaxis (that is, the arrangement of the features) there. It is shown how two parameters determine on which conspicuous spirals successive features are in contact at any point, whether the numbers of intersecting spirals change from point to point, and, if so, through what values. These parameters are the divergence δ, which is assumed to be constant, and a quantity ξ, which is the reciprocal of the normalized rise, and which in general varies from point to point. Finally, it is proved that Fibonacci phyllotaxis (in which the numbers of intersecting spirals are always Fibonacci numbers) produces greater packing efficiency than any other, provided that the lattice varies over the surface.     

Maintaining the status quo: T-cell homeostasis

Lymphocyte numbers and subset composition are maintained at relatively constant levels throughout adulthood. Fluctuations in cell numbers due to infection, loss of cells, or other influences are smoothed out by unknown mechanisms that return the system to homeostasis. Regulation of lymphocyte numbers could be controlled at several points: rate of production, alteration in life span by diminution or enhancement of survival, or by division of cells within the compartment. Cell numbers within the immune system appear to be controlled by homeostatic mechanisms that influence each of these points. This discussion will focus on the regulation of peripheral cell numbers by the antigen-independent proliferation of T cells, which has recently been demonstrated to contribute to the maintenance and recovery of lymphocyte homeostasis.     

The Occurrence of Clostridia on Bacon Slaughter Lines

Safety in the production of canned meat products depends on the numbers of heat resistant clostridia in the product before processing, as the effect of heat processing is limited. For this reason, the numbers of clostridia in the raw materials are of great importance, and any method which may reduce these numbers is of value.
This investigation has shown that clostridia are present on the rind side of pig carcases at various stages during slaughter operations, the numbers depending on the bacteriological state of the slaughtering equipment. In addition, frozen sections have indicated the presence of clostridia in the deeper layers of the skin. Washing the carcases with hot water besides lowering the aerobic count also reduces the numbers of clostridia.     

Does competition or facilitation regulate migrant ungulate populations in the Serengeti? A test of hypotheses

Summary Interspecific competition and facilitation have both been proposed as processes promoting species separation and co-existence in African ungulates. In one group of grazers on the Serengeti plains, comprising wildebeest (Connochaetes taurinus), zebra (Equus burchelli), and Thomson's gazelle (Gazella thomsoni), these processes have also been suggested to regulate the populations. Censuses of these populations over 20 years have shown changes that allow a test of which, if either, process regulates population numbers. Wildebeest numbers have levelled off as a result of intraspecific competition for food following a five-fold increase due to release from disease and an increase in food supply. Zebra numbers have remained stationary throughout the same period. Gazelle numbers have declined in the last 10 years. These results are contrary to the facilitation hypothesis, which predicts that wildebeest numbers should not have increased if those of zebra did not, and that gazelle numbers should have increased since the wildebeest population increased. The gazelle results are consistent with the interspecific competition hypothesis, but the zebra results are contrary to it. We propose an alternative hypothesis that predation regulates the zebra population, and we suggest ways of testing this.     

The distribution of organic cores, cones, cone junctions and pores in the egg shells of wild birds

Egg shells from 14 widely different species of wild birds were examined, using collodion casts of the inside surface of the shell. Organic cores, cones, cone junctions and pores were counted and in each case measurements of nearest neighbour distances were taken. Shell thickness was also measured.
It was found that, using mean values for each egg shell, there were highly significant, and in some cases almost perfect linear relationships between core numbers, cone numbers, cone junction numbers and pore numbers on the one hand and their respective nearest neighbour distances expressed as the reciprocal of the mean of the squares of these distances on the other. The results also showed that the distribution of all four structures was not random, but had a degree of uniformity increasing up the series pores < cone junctions < cores < cones.
The following relationships were also highly significant: core and cone numbers, core and cone junction numbers, and cone and cone junction numbers. The relationship of pore numbers to any of the other three structures was of no great significance.
Shell thickness was related curvilinearly to core numbers and to cone numbers and linearly to nearest neighbour values for cones. It was also related to pore numbers.
It is suggested that, apart from pores the other three structures and their distribution all depend upon the number of cores which are the original centres of crystallization from which the shell grows. To a lesser extent shell thickness also depends upon these structures. Tentative suggestions are also made concerning the origin of the pores.     

VISCIN THREADS,POLLINATION EFFICIENCY AND LOW POLLEN-OVULE RATIOS

Some Onagraceae are characterized by quite low pollen-ovule ratios. We suggest they are an evolutionary response to highly efficient pollination, mediated through viscin threads, which hold large numbers of pollen grains together, and by stigmas, which are large relative to the area of the pollinator over which the pollen is spread. The pollen grains of some Leguminosae are joined by “exinal connections” which are chemically and morphologically similar to viscin threads. In the legumes the area of the stigma is small relative to the area of pollen on the pollinator and pollination is facilitated by short connections which hold small numbers of pollen grains together.     

Computer-Produced Labels Protected by Lamination in Mylar for Histological Specimens

Keeping track of specimens during processing in large histopathology laboratories requires adequate labeling. For several years we tried various methods of treating cardboard tags bearing typed numbers, which are often used. These tags are satisfactory for some processing fluids but are acted upon by others, especially corrosive fixatives and some solvents (e.g. benzene, toluene, and ether). The typed numbers often dissolve, the ink runs, and the numbers become illegible. Dipping into melted paraffin, painting with shellac, or dipping into a solution of epoxy resin are not satisfactory treatments.     

Models of Hopfield-type quaternion neural networks and their energy functions

Recently models of neural networks that can directly deal with complex numbers, complex-valued neural networks, have been proposed and several studies on their abilities of information processing have been done. Furthermore models of neural networks that can deal with quaternion numbers, which is the extension of complex numbers, have also been proposed. However they are all multilayer quaternion neural networks. This paper proposes models of fully connected recurrent quaternion neural networks, Hopfield-type quaternion neural networks. Since quaternion numbers are non-commutative on multiplication, some different models can be considered. We investigate dynamics of these proposed models from the point of view of the existence of an energy function and derive their conditions for existence.     

栌菊木属及白菊木属的细胞学研究

对栌菊木属及白菊木属的染色体数目进行了首次报道,对栌菊木（Nouelia insignis Franch.)分布区内的10个居群进行了细胞学研究,染色体数目均为2n=54。白菊木属在中国分布的仅白菊木（Leucomeris decora Kurz)一种,对漾濞这个居群的细胞学研究表明,染色体也为2n=54。这两个属的基数可能x=9,它们可能为6倍体,结合帚木菊族已有染色体报道及形态特征,地理分布等初步分析表明：栌菊木种内分化程度小,是一自然类群;栌菊木和白菊木可能有着较近缘的联系;栌菊木可能是古老孑遗植物的后裔,为适应环境而多倍体化,得以保存下来。     

Elusive data underlying debate at the prokaryote-eukaryote divide

Background

The origin of eukaryotic cells was an important transition in evolution. The factors underlying the origin and evolutionary success of the eukaryote lineage are still discussed. One camp argues that mitochondria were essential for eukaryote origin because of the unique configuration of internalized bioenergetic membranes that they conferred to the common ancestor of all known eukaryotic lineages. A recent paper by Lynch and Marinov concluded that mitochondria were energetically irrelevant to eukaryote origin, a conclusion based on analyses of previously published numbers of various molecules and ribosomes per cell and cell volumes as a presumed proxy for the role of mitochondria in evolution. Their numbers were purportedly extracted from the literature.

Results

We have examined the numbers upon which the recent study was based. We report that for a sample of 80 numbers that were purportedly extracted from the literature and that underlie key inferences of the recent study, more than 50% of the values do not exist in the cited papers to which the numbers are attributed. The published result cannot be independently reproduced. Other numbers that the recent study reports differ inexplicably from those in the literature to which they are ascribed. We list the discrepancies between the recently published numbers and the purported literature sources of those numbers in a head to head manner so that the discrepancies are readily evident, although the source of error underlying the discrepancies remains obscure.

Conclusion

The data purportedly supporting the view that mitochondria had no impact upon eukaryotic evolution data exhibits notable irregularities. The paper in question evokes the impression that the published numbers are of up to seven significant digit accuracy, when in fact more than half the numbers are nowhere to be found in the literature to which they are attributed. Though the reasons for the discrepancies are unknown, it is important to air these issues, lest the prominent paper in question become a point source of a snowballing error through the literature or become interpreted as a form of evidence that mitochondria were irrelevant to eukaryote evolution.

Reviewers

This article was reviewed by Eric Bapteste, Jianzhi Zhang and Martin Lercher.