Zonation and regulation of old pasture populations of Hieracium floribundum

1974 ◽  
Vol 52 (7) ◽  
pp. 1451-1458 ◽  
Author(s):  
A. G. Thomas ◽  
H. M. Dale
Keyword(s):  
Population Growth ◽  
Central Zone ◽  
Outer Zone ◽  
Flowering Plant ◽  
Flower Production

Colonies of the perennial Hieracium floribundum Wimm. and Grab, had four zones, identified by the density of the rosettes. Belts of sod were analyzed to determine the characteristics of these zones in a pasture which had not been grazed for 5 years. The advancing outer zone consisted of widely spaced rosettes that were less than 2 years old. These rosettes had short rhizomes and large leaves, reproduced by stolons, and flowered abundantly, producing numerous heads per inflorescence. In the central zone, which had the highest density, the rosettes were more than 2 years old, had long rhizomes and small leaves, and did not flower. Seedling numbers were insignificant in all zones. In this species stolons are produced only on plants that have flowered. At high densities curtailment of population growth resulted from reduced flower production and the number of associated stolons initiated per flowering plant.

Basidiocarp development in Calocera cornea

1972 ◽  
Vol 50 (3) ◽  
pp. 413-417 ◽  
Author(s):  
Lorene L. Kennedy
Keyword(s):  
Relative Humidity ◽  
Rapid Growth ◽  
Structural Unit ◽  
Central Zone ◽  
Outer Zone ◽  
Carotenoid Pigments ◽  
Gel Formation ◽  
Median Zone

The development of the basidiocarp of Calocera cornea in the natural and cultural environments is described. The structural unit is a narrow, unmodified hypha with the capacity for pigment and gel formation. In the basidiocarp the hyphae become organized into a central zone of compact, parallel hyphae, a median zone of interwoven hyphae with numerous spaces containing gelatinous material, and an outer zone composed of bifurcate basidia each bearing two basidiospores.Primordia and basidiocarps show rapid growth with marked sensitivity to relative humidity and sporulation frequently takes place before basidiocarp development is complete. Short periods of rapid growth alternate with long periods of inactivity during which the formation of fungal gel and carotenoid pigments probably aids in survival.

scholarly journals Temporal dynamics of sexual dimorphism in a dioecious species

2020 ◽  
Vol 126 (3) ◽  
pp. 471-480
Author(s):  
L Moquet ◽  
L Lateur ◽  
A-L Jacquemart ◽  
I De Cauwer ◽  
M Dufay
Keyword(s):  
Sexual Dimorphism ◽  
Plant Species ◽  
Temporal Dynamics ◽  
Flower Size ◽  
Flowering Plant ◽  
Floral Traits ◽  
Flower Number ◽  
Pollinator Behaviour ◽  
Flower Production ◽  
Flowering Season

Abstract Background and Aims Sexual dimorphism for floral traits is common in dioecious plant species. Beyond its significance for understanding how selection acts on plant traits through male vs. female reproductive function, sexual dimorphism has also been proposed as a possible risky characteristic for insect-pollinated plants, as it could drive pollinators to forage mostly on male plants. However, even though most flowering plant species spread their flowering across several weeks or months, the temporal variation of floral phenotypes and sexual dimorphism have rarely been investigated. Methods We performed a survey of male and female plants from the dioecious generalist-pollinated Silene dioica (Caryophyllaceae) in a common garden experiment, over two consecutive flowering seasons. Flower number and floral size were measured each week, as well as pollen quantity and viability in male plants. Key Results Sexual dimorphism was found for all investigated floral traits, with males showing an overall higher investment in flower production and flower size. Males and females showed a similar temporal decline in flower size. The temporal dynamics of daily flower number differed between sexes, with males showing a peak in the middle of their flowering season, whereas flower production by females was quite stable over time. At the scale of the experimental population, both individual and floral sex ratios appeared to vary across the flowering season. Moreover, because the onset of flowering varied among plants, the magnitude of sexual dimorphism in floral size also fluctuated strongly through time. Conclusions Capturing male/female differences with only one temporal measurement per population may not be informative. This opens stimulating questions about how pollinator behaviour and resulting pollination efficiency may vary across the flowering season.

scholarly journals Myelin-associated glycoprotein and myelinating Schwann cell-axon interaction in chronic B,B'-iminodipropionitrile neuropathy.

1984 ◽  
Vol 98 (4) ◽  
pp. 1272-1278 ◽  
Author(s):  
B D Trapp ◽  
R H Quarles ◽  
J W Griffin
Keyword(s):  
Schwann Cell ◽  
Central Zone ◽  
Minor Component ◽  
Outer Zone ◽  
Structural Protein ◽  
Myelinated Fibers ◽  
Pns Myelin ◽  
Myelin Associated Glycoprotein ◽  
Myelinating Schwann Cell ◽  
Periaxonal Space

The myelin-associated glycoprotein (MAG) is a heavily glycosylated integral membrane glycoprotein which is a minor component of isolated rat peripheral nervous system (PNS) myelin. Immunocytochemically MAG has been localized in the periaxonal region of PNS myelin sheaths. The periaxonal localization and biochemical features of MAG are consistent with the hypothesis that MAG plays a role in maintaining the periaxonal space of myelinated fibers. To test this hypothesis, MAG was localized immunocytochemically in 1-micron sections of the L5 ventral root from rats exposed to B,B'-iminodipropionitrile. In chronic states of B,B'-iminodipropionitrile intoxication, Schwann cell periaxonal membranes and the axolemma invaginate into giant axonal swellings and separate a central zone of normally oriented axoplasm from an outer zone of maloriented neurofilaments. Ultrastructurally, the width of the periaxonal space (12-14 nm) in the ingrowths is identical to that found in normally myelinated fibers. These Schwann cell ingrowths which are separated from compact myelin by several micra are stained intensely by MAG antiserum. Antiserum directed against Po protein, the major structural protein of compact PNS myelin, does not stain the ingrowths unless compact myelin is present. These results demonstrate the periaxonal localization of MAG and support a functional role for MAG in maintaining the periaxonal space of PNS myelinated fibers.

Viscous flow past a flat plate with uniform injection

1965 ◽  
Vol 284 (1398) ◽  
pp. 370-396 ◽  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Numerical Study ◽  
Central Zone ◽  
Outer Zone ◽  
Analytic Study ◽  
Boundary Layer Equations ◽  
Numerical Studies ◽  
High Degree ◽  
Uniform Injection

The boundary-layer equations for an incompressible fluid in motion past a flat plate are examined, numerically and analytically, in the special case when the pressure gradient vanishes and there is a uniform injection of fluid from the plate. In the numerical study the principal properties of the boundary layer are computed as far as separation ( x ═ x δ ≑ 0.7456) with a high degree of accuracy. In the analytic study the structure of the singularity at separation is determined. It is of a new kind in boundary layer theory and its elucidation requires the division of the boundary layer into three zones—an outer zone in which the non-dimensional velocity u is much larger than x * (the non-dimensional distance from separation), a central zone in which u ~ x * and an inner zone in which u ≪ x *. A match is effected between solutions in the central and inner zones from which it is inferred that the skin friction τ 0 ~ ( x * / In (1/ x *) 2 as x * → 0. A completely satisfactory agreement between the numerical and analytic studies was not possible. The reason is that the analytic study is only valid when ln ( 1 / x *) ≫ 1 which means that for the analytic and numerical studies to have a common region of validity, the numerical integration must be extended to much smaller values of x * than is possible at present. It was also not possible to effect a match between the central and outer zones in the analytic solution due to the difficulty of finding the properties of the stress τ in the central zone as u / x * →∞.

Complexly zoned niobian titanite from hedenbergite skarn at Písek, Czech Republic, constrained by substitutions Al(Nb,Ta)Ti—2, Al(F,OH)(TiO)—1 and SnTi—1

2008 ◽  
Vol 72 (6) ◽  
pp. 1293-1305 ◽  
Author(s):  
J. Cempírek ◽  
S. Houzar ◽  
M. Novák
Keyword(s):  
Crystal Structure ◽  
Czech Republic ◽  
Negative Relationship ◽  
Central Zone ◽  
Outer Zone ◽  
Formula Unit ◽  
Core Zone ◽  
The Core ◽  
Native Bismuth ◽  
Relationship Of

AbstractEuhedral crystals of complexly zoned niobian titanite (up to 0.3 mm) are enclosed in hedenbergite (Hd53—81Di15—43Jh3-5) and quartz from a hedenbergite vein skarn at Kamenne doly near Pisek, Czech Republic. They are associated with minor clinozoisite-epidote (Ps3—22), calcite, plagioclase (An95). scapolite (Me80—82), scheelite, pyrrhotite, fluorapatite, arsenopyrite, native bismuth and Bi,Te-minerals. The following textural and compositional subtypes were recognized: (I) Nb-rich titanite, (II) Nb-moderate titanite in the central zone, (III) Nb-poor, Sn-enriched titanite and (IV) Nb-poor, Al,F-rich titanite in the outer zone. The substitution Al(Nb,Ta)Ti—2 is dominant in subtypes I and II, the titanite subtype I being characterized by elevated contents of Al ≤ 0.257 atoms per formula unit (a.p.f.u.), Nb (≤ 0.161 a.p.f.u.) and Ta (≤ 0.037 a.p.f.u.). Amounts of Al, Nb and Ta in subtype II are smaller and more variable. The minor substitution SnTi—1 occurs chiefly in titanite subtype III with a content of Sn ≤ 0.039 a.p.f.u.. The substitution Al(F,OH)(TiO)_i is typical for titanite subtype IV exhibiting elevated contents of Al (s£ 0.221 a.p.f.u.), F (≤ 0.196 a.p.f.u.) and Fe (≤ 0.039 a.p.f.u.).The negative relationship of substitutions Al(F,OH)(TiO)_i vs. SnTi—1 and Al(Nb,Ta)Ti—1 is constrained chiefly by crystal structure rather than by the composition of parent medium alone. Textural relations suggest that the Nb-moderate titanite in the core zone and entire outer zone are products of fluids-induced dissolution-reprecipitation processes. The studied niobian titanite represents a new F-enriched type from a medium-grade, calc-silicate rock.

Petrology of the Turnagain ultramafic complex, northwestern British Columbia

1980 ◽  
Vol 17 (6) ◽  
pp. 744-757 ◽  
Author(s):  
Thomas Clark
Keyword(s):  
Volcanic Rocks ◽  
Central Zone ◽  
Minor Element ◽  
Outer Zone ◽  
Late Triassic ◽  
Small Scale ◽  
Chrome Spinel ◽  
Low Oxygen ◽  
Nickel Copper ◽  
Ultramafic Complex

The Turnagain ultramafic complex is an Alaskan-type complex of possible Late Triassic age. It has a central zone of dunite and an outer zone of wehrlite, olivine clinopyroxenite, clinopyroxenite, dunite, hornblendite (rare), and basic hornblende and plagioclase-bearing rock (rare). The complex is largely fault-bounded. The central dunite intrudes the pyroxene-bearing rocks in one area; elsewhere the two zones are gradational. Small-scale layering occurs locally, and is most common in the outer zone. Layering dips steeply due to folding during regional deformation. The ultramafic rocks are generally only partly serpentinized, and consist largely of olivine, clinopyroxene, pargasite, phlogopite, and chrome spinel. The outer zone contains sporadic concentrations of iron–nickel–copper sulfides. Olivine is most magnesian (Fo94.9) in the central dunite, and most iron-rich (Fo80.2) in olivine clinopyroxenite. Clinopyroxene is diopside and follows an iron-enrichment trend. Minor-element contents of minerals indicate that crystallization caused magmatic impoverishment in Ni and Cr, and enrichment in Ti and Al. The primitive Turnagain magma was probably ultrabasic, extremely magnesian, and poor in Al and Ti. Differentiation followed an alkalic trend, possibly at relatively low oxygen fugacity compared to other Alaskan-type complexes. The complex may have formed in a subvolcanic magma chamber, and thus be related to nearby Upper Triassic volcanic rocks.

Methodology of High-Carbon Wire Rod Perlite Grain Grade Identification

2018 ◽  
Vol 284 ◽  
pp. 338-343 ◽  
Author(s):  
I.G. Shubin ◽  
M.V. Shubina
Keyword(s):  
Steel Wire ◽  
High Carbon Steel ◽  
Central Zone ◽  
Outer Zone ◽  
Point Of View ◽  
High Carbon ◽  
Wire Rod ◽  
Improved Technique ◽  
Selection Of

The quality of the high-carbon rod is determined by mechanical properties, which depend on microstructure characteristics, in particular the perlite grain grade. The existing technique for determining the perlite dispersion has the main drawback - the subjectivity of choosing the five worst view fields for evaluation, which reduces the accuracy of the determination results. The article presents the results of a study aimed at increasing the objectivity and accuracy of the evaluation of high-carbon wire rod perlite grain grade. An improved technique for determining the high-carbon wire rod perlite grain grade – Pgg with five view fields is proposed. The cross-section of the rod sample is considered as an inhomogeneous area from the perlite dispersion point of view, which is divided into three annular zones with different levels of perlite dispersion. Selection of five view fields is carried out as follows: one from the center of the central zone, two fields in the second - an intermediate zone and two fields in the outer zone. Statistical analysis of the experimental data showed that all view fields should be located on the same diagonal. The location of the view fields is fixed and is unchangeable for all samples under study. The technique described in the article is an effective tool for analyzing the structure of high-carbon steel wire rod.

scholarly journals Severe Plastic Deformation of Fe-22Al-5Cr Alloy by Cross-Channel Extrusion with Back Pressure

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2214 ◽  
Author(s):  
Radosław Łyszkowski ◽  
Wojciech Polkowski ◽  
Tomasz Czujko
Keyword(s):  
Triaxial Compression ◽  
Central Zone ◽  
Outer Zone ◽  
Back Pressure ◽  
Material Structure ◽  
Original Material ◽  
Accumulated Strain ◽  
Strong Deformation ◽  
Number Of Passes ◽  
Deformation Homogeneity

A new concept of the cross-channel extrusion (CCE) process under back pressure (BP) was proposed and tested experimentally. The obtained by finite element method (FEM) results showed that a triaxial compression occurred in the central zone, whereas the material was deformed by shearing in the outer zone. This led to the presence of a relatively uniformly deformed outer zone at 1 per pass and a strong deformation of the paraxial zone (3–5/pass). An increase in the BP did not substantially affect the accumulated strain but made it more uniform. The FEM results were verified using the physical modeling technique (PMT) by the extrusion of clay billet. The formation of the plane of the strongly flattened, and elongated grains were observed in the extrusion directions. With the increase in the number of passes, the shape of the resulting patterns expanded, indicating an increase in the deformation homogeneity. Finally, these investigations were verified experimentally for Fe-22Al-5Cr (at. %) alloy using of the purposely designed tooling. The effect of the CCE process is the fragmentation of the original material structure by dividing the primary grains. The complexity of the stress state leads to the rapid growth of microshear bands (MSB), grain defragmentation and the nucleation of new dynamically recrystallized grains about 200–400 nm size.

Intramitochondrial Viruses of Reptilian Cell Origin

1972 ◽  
Vol 30 ◽  
pp. 318-319
Author(s):  
Philip D. Lunger ◽  
H. Fred Clark
Keyword(s):  
Particle Production ◽  
Outer Zone ◽  
Density Variation ◽  
Core Region ◽  
Mitochondrial Membranes ◽  
Virus Particles ◽  
The Core ◽  
Vipera Russelli ◽  
Maturation Stages ◽  
Type Particle

In the course of fine structure studies of spontaneous “C-type” particle production in a viper (Vipera russelli) spleen cell line, designated VSW, virus particles were frequently observed within mitochondria. The latter were usually enlarged or swollen, compared to virus-free mitochondria, and displayed a considerable degree of cristae disorganization.Intramitochondrial viruses measure 90 to 100 mμ in diameter, and consist of a nucleoid or core region of varying density and measuring approximately 45 mμ in diameter. Nucleoid density variation is presumed to reflect varying degrees of condensation, and hence maturation stages. The core region is surrounded by a less-dense outer zone presumably representing viral capsid.Particles are usually situated in peripheral regions of the mitochondrion. In most instances they appear to be lodged between loosely apposed inner and outer mitochondrial membranes.

Perspectives on Development and Population Growth in the Third World

1990 ◽  
Vol 44 (3) ◽  
pp. 524-525
Author(s):  
Allan G. Hill
Keyword(s):  
Population Growth ◽  
Third World ◽  
The Third ◽  
The Third World
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