Morphometric analysis of Rhynia and Asteroxylon: testing functional aspects of early land plant evolution

Paleobiology ◽  
2000 ◽  
Vol 26 (3) ◽  
pp. 405-418 ◽  
Author(s):  
A. Roth-Nebelsick ◽  
G. Grimm ◽  
V. Mosbrugger ◽  
H. Hass ◽  
H. Kerp
Keyword(s):  
Water Transport ◽  
Land Plant ◽  
Plant Evolution ◽  
Cross Sectional Area ◽  
Land Plants ◽  
Limiting Factor ◽  
Vascular Bundles ◽  
Sectional Area ◽  
Cross Sectional ◽  
Early Land

New morphometric data gathered from cross-sections of two Lower Devonian land plants (Rhynia gwynne-vaughanii and Asteroxylon mackiei) are interpreted in terms of the evolution of the function of vascular bundles in early land plants. The following conclusions can be drawn from these new data: (1) The ratio of the cross-sectional area of the xylem (representing the conducting volume supplying the axis with water) to the xylem perimeter (representing the “contact area” between xylem and parenchyma through which water leaves the xylem and enters the parenchyma) is not constant for Rhynia axes, almost constant for Asteroxylon axes, and different between Rhynia and Asteroxylon. Thus, Bowers hypothesis that the ratio of cross-sectional area of the xylem to xylem perimeter is constant during ontogenetic development is true for Asteroxylon. That this ratio is constant during phylogeny, however, is not supported by our data. (2) The ratio between cross-sectional area of xylem to parenchyma is higher in Asteroxylon than in Rhynia. (3) As predicted by previous computer simulations, the ratio of the xylem perimeter to the axis perimeter plays a major role in determining water transport performance of the transpiring axis. This ratio is constant within ontogeny but is different in Asteroxylon and Rhynia. In Asteroxylon axes, this ratio is about twice as large as in Rhynia axes. (4) Contrary to the expectations, the distance between the outermost layer of the xylem and the transpiring surface, which represents the low-conductivity pathway through the parenchyma, appears not to be a limiting factor for the water transport in axes of Rhynia and Asteroxylon. (5) From the analysis of the geometric parameters, it is evident that Rhynia and Asteroxylon with their distinct stelar geometries represent two different constructional types for which no transitional stages are known.

Numerical studies of water conduction in land plants: evolution of early stele types

Paleobiology ◽  
1996 ◽  
Vol 22 (3) ◽  
pp. 411-421 ◽  
Author(s):  
Anita Roth ◽  
Volker Mosbrugger
Keyword(s):  
Transport Properties ◽  
Water Transport ◽  
Vascular Tissue ◽  
Plant Evolution ◽  
Cross Sectional Area ◽  
Functional Explanation ◽  
Sectional Area ◽  
Cross Sectional ◽  
Water Conduction ◽  
Water Transport Properties

During land plant evolution, a change in stelar architecture, i.e., in the geometric arrangement of the water-conducting tissue inside the plant axis, can be observed. In the most primitive stele type, the protostele, the vascular tissue is organized as a simple central strand. Further evolutionary changes led to more peripherally arranged vascular tissues. In the siphonostele, for example, the vascular tissue forms a hollow cylinder filled with pith. A functional explanation of this early stelar evolution is provided in the present paper. Using a numerical simulation approach, we analyze the water transport properties of various protostelic and siphonostelic model axes. The results indicate that several geometric parameters are relevant for understanding the water transport properties of various stele types and for explaining the early stelar evolution: the parenchymatic path lengths (i.e., the distance between the xylem surface and the transpiring plant surface), the ratio of xylem surface over transpiring surface, and the ratio of cross-sectional area of xylem to cross-sectional area of the parenchyma outside of the xylem. As a whole, the evolution of early stele types may be viewed as a size-related multi-criteria optimization process in which the xylem volume as well as the fluid pressure gradients in the parenchyma and in the xylem are minimized. For slender plant axes, a protostele appears to be the optimal stelar architecture. In wider plant axes, however, other stelar architectures (such as a siphonostele) prove to be more efficient than a protostele.

Age of the Cedarberg Formation, South Africa and early land plant evolution

1986 ◽  
Vol 123 (4) ◽  
pp. 445-454 ◽  
Author(s):  
J. Gray ◽  
J. N. Theron ◽  
A. J. Boucot
Keyword(s):  
South Africa ◽  
Land Plant ◽  
Plant Evolution ◽  
Marine Phytoplankton ◽  
Land Plants ◽  
Table Mountain ◽  
Plant Remains ◽  
First Occurrence ◽  
Land Plant Evolution ◽  
Early Land

AbstractThe first occurrence of Early Paleozoic land plants is reported from South Africa. The plant remains are small, compact tetrahedral spore tetrads. They occur abundantly in the Soom Shale Member of the Cedarberg Formation, Table Mountain Group. Marine? phytoplankton (sphaeromorphs or leiospheres) occur with the spore tetrads in all samples. Rare chitinozoans are found in half the samples. Together with similar spore tetrads from the Paraná Basin (Gray et al. 1985) these are the first well-documented records of Ashgill and/or earlier Llandovery land plants from the Malvinokaffric Realm, and from the African continent south of Libya. These spore tetrads have botanical, evolutionary, and biogeographic significance. Their size in comparison with spore tetrads from stratigraphic sections throughout eastern North America, suggests that an earliest Llandovery age is more probable for the Soom Shale Member, although a latest Ordovician age cannot be discounted. The age of the brachiopods in the overlying Disa Siltstone Member has been in contention for over a decade. Both Ashgillian and Early Llandovery ages have been proposed. The age of the underlying Soom Shale Member based on plant spores and trilobites (earliest Llandovery or latest Ashgillian) suggests that the Disa Siltstone Member is also likely to be of Early Llandovery age, although the distance between the Soom Shale Member spore-bearing locality and rocks to the south yielding abundant invertebrate body fossils at one locality is great enough to permit diachroneity.

Physical strength and its relation to leaf anatomical characteristics of nine forage grasses

2004 ◽  
Vol 52 (6) ◽  
pp. 799 ◽  
Author(s):  
Ji Min Zhang ◽  
Akio Hongo ◽  
Masahiro Akimoto
Keyword(s):  
Shear Strength ◽  
Festuca Arundinacea ◽  
Dactylis Glomerata ◽  
Cross Sectional Area ◽  
Vascular Bundles ◽  
Sectional Area ◽  
Forage Grasses ◽  
Cross Sectional ◽  
Anatomical Characteristics ◽  
Physical Strength

Nine species of forage grasses (five C3 species and four C4 species) were planted in a controlled-environment glasshouse. The C3 plants were Festuca arundinacea Schreb, Dactylis glomerata L., Phleum pratense L., Lolium perennel L. and Poa pratensis L.; the C4 plants were Chloris gayana Kunch., Cynodon dactylon (L.) Pers., Paspalum dilatatum Poir. and Sorghum halenpense (L.) Pers. The number of major vascular bundles and minor vascular bundles, cross-sectional area, the area and proportion of sclerenchyma in a cross-section, thickness of leaf blade, and tensile and shear strength were investigated in order to determine the relationship between physical strength and anatomical characteristics. Physical strength and anatomical characteristics of leaf blades showed significant (P < 0.01) variation between species. Significant correlations were detected between tensile strength and cross-sectional area in forage grasses except Festuca arundinacea. Festuca arundinacea, Dactylis glomerata, Phleum pratense, Chloris gayana and Sorghum halenpense showed significant correlations of tensile strength with the number of major vascular bundles. Festuca arundinacea, Dactylis glomerata and Lolium perennel showed significant correlations of shear strength with cross-sectional area. Festuca arundinacea, Dactylis glomerata and Paspalum dilatatum showed significant correlations of shear strength with the number of major vascular bundles. The proportion of sclerenchyma in a cross-section showed poor correlations with tensile and shear strength. Thickness of leaf blade showed poor correlations with tensile and shear strength except in Dactylis glomerata. Physical strength and anatomical characteristics of leaf blades of the C3 group differed significantly (P < 0.01) when compared with the C4 group except for cross-sectional area. Tensile and shear strength showed significant correlations with cross-sectional area, sclerenchyma area and the number of vascular bundles when all nine species were treated as one group.

scholarly journals The timescale of early land plant evolution

2018 ◽  
Vol 115 (10) ◽  
pp. E2274-E2283 ◽  
Author(s):  
Jennifer L. Morris ◽  
Mark N. Puttick ◽  
James W. Clark ◽  
Dianne Edwards ◽  
Paul Kenrick ◽  
...  
Keyword(s):  
Molecular Clock ◽  
Fossil Record ◽  
Land Plant ◽  
Plant Evolution ◽  
Land Plants ◽  
Early Land Plant ◽  
Land Plant Evolution ◽  
The Impact ◽  
Earth’S System ◽  
Early Land

Establishing the timescale of early land plant evolution is essential for testing hypotheses on the coevolution of land plants and Earth’s System. The sparseness of early land plant megafossils and stratigraphic controls on their distribution make the fossil record an unreliable guide, leaving only the molecular clock. However, the application of molecular clock methodology is challenged by the current impasse in attempts to resolve the evolutionary relationships among the living bryophytes and tracheophytes. Here, we establish a timescale for early land plant evolution that integrates over topological uncertainty by exploring the impact of competing hypotheses on bryophyte−tracheophyte relationships, among other variables, on divergence time estimation. We codify 37 fossil calibrations for Viridiplantae following best practice. We apply these calibrations in a Bayesian relaxed molecular clock analysis of a phylogenomic dataset encompassing the diversity of Embryophyta and their relatives within Viridiplantae. Topology and dataset sizes have little impact on age estimates, with greater differences among alternative clock models and calibration strategies. For all analyses, a Cambrian origin of Embryophyta is recovered with highest probability. The estimated ages for crown tracheophytes range from Late Ordovician to late Silurian. This timescale implies an early establishment of terrestrial ecosystems by land plants that is in close accord with recent estimates for the origin of terrestrial animal lineages. Biogeochemical models that are constrained by the fossil record of early land plants, or attempt to explain their impact, must consider the implications of a much earlier, middle Cambrian–Early Ordovician, origin.

scholarly journals The Phloem of the Wheat Stem in Relation to Requirements for Assimilate by The Ear

1970 ◽  
Vol 23 (4) ◽  
pp. 743 ◽  
Author(s):  
LT Evans ◽  
RL Dunstone ◽  
HM Rawson ◽  
RF Williams
Keyword(s):  
Light Intensity ◽  
Wild Species ◽  
High Light Intensity ◽  
High Light ◽  
Cross Sectional Area ◽  
Main Stem ◽  
Vascular Bundles ◽  
Sectional Area ◽  
Cross Sectional ◽  
Related Wild Species

The cross-sectional area of the phloem and the number of vascular bundles at the top of the main stem were determined in 22 diploid, tetraploid, and hexaploid wheats and related wild species grown at 21{16�C in 16-hr days of high light intensity.

The nature of reaction wood. IX. Anomalous cases of reaction anatomy

1964 ◽  
Vol 12 (2) ◽  
pp. 173 ◽  
Author(s):  
G Scurfield
Keyword(s):  
Cross Sectional Area ◽  
Axial Position ◽  
Vertical Position ◽  
Reaction Wood ◽  
Vascular Bundles ◽  
Sectional Area ◽  
Cross Sectional ◽  
Gelatinous Layer ◽  
Stage Of Development ◽  
Wood Fibres

The reaction anatomy of 14 species of Acacia, Lagunaria pattersoni, and the woody monocotyledons Dracaena fragrans and D. marginata was examined with light, polarizing, and ultraviolet microscopes. Notable features of the reaction wood fibres of Acacia spp. were: the absence of birefringence in the sublayers of the "gelatinous" layer at all stages of their deposition; the absence of radial striations in the gelatinous layer; the frequency of occurrence of fibres lacking protoplasts and with convoluted gelatinous layers at some intermediate stage of development; the relatively wide separation of stages of gelatinous layer formation in passing from cambium towards pith; and the poor adherence of the gelatinous layer to previously formed cell wall layers. It was concluded that the forces bringing about gelatinous layer deposition were either weaker or slower to develop, or both, than in species such as Tristania conferta. Possible reasons for this are discussed. Deposition of starch grains in reaction wood fibres occurred in all Acacia spp, towards the end of the growing season. A gelatinous layer did not occur in reaction wood fibres of Lagunaria pattersoni. These differed from normal fibres only in the thinness of their walls and their relatively large cross-sectional area. Examination of the wall structure of phloem fibres indicated that changes in microfibril orientation towards a more axial position which occurred in layer S2 of primary phloem fibres were accelerated on the upper sides of bent stems. The significance of this feature, and of possible tensions developed in the outer cortex and epidermis on the upper sides of bent stems because of accelerated phloem and xylem development, are discussed in relation to mechanisms whereby such stems may recover to a vertical position. The number of vascular bundles and the wall thickness and extent of lignification of the fibres of the bundle sheaths, were increased on the upper sides of horizontally grown stems of Dracaena spp. The radial width of the cortex and the cross-sectional area of cortical cells were less than on the lower sides of the stems.

Pelvic Canal Narrowing Caused by Triple Pelvic Osteotomy in the Dog

1994 ◽  
Vol 07 (03) ◽  
pp. 110-113 ◽  
Author(s):  
D. L. Holmberg ◽  
M. B. Hurtig ◽  
H. R. Sukhiani
Keyword(s):  
Postoperative Complications ◽  
Pelvic Osteotomy ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Canal Width ◽  
Operative Complications ◽  
Post Operative Complications

SummaryDuring a triple pelvic osteotomy, rotation of the free acetabular segment causes the pubic remnant on the acetabulum to rotate into the pelvic canal. The resulting narrowing may cause complications by impingement on the organs within the pelvic canal. Triple pelvic osteotomies were performed on ten cadaver pelves with pubic remnants equal to 0, 25, and 50% of the hemi-pubic length and angles of acetabular rotation of 20, 30, and 40 degrees. All combinations of pubic remnant lengths and angles of acetabular rotation caused a significant reduction in pelvic canal-width and cross-sectional area, when compared to the inact pelvis. Zero, 25, and 50% pubic remnants result in 15, 35, and 50% reductions in pelvic canal width respectively. Overrotation of the acetabulum should be avoided and the pubic remnant on the acetabular segment should be minimized to reduce postoperative complications due to pelvic canal narrowing.When performing triple pelvic osteotomies, the length of the pubic remnant on the acetabular segment and the angle of acetabular rotation both significantly narrow the pelvic canal. To reduce post-operative complications, due to narrowing of the pelvic canal, overrotation of the acetabulum should be avoided and the length of the pubic remnant should be minimized.

DETERMINATION OF THE FUNCTION OF THE ROD’S CROSS-SECTIONAL AREA USING VIBRATION EIGENFREQUENCIES

2020 ◽  
Vol 0 (4) ◽  
pp. 19-24
Author(s):  
I.M. UTYASHEV ◽  
◽  
A.A. AITBAEVA ◽  
A.A. YULMUKHAMETOV ◽  
◽  
...  
Keyword(s):  
Cross Sectional Area ◽  
Variable Cross ◽  
Sectional Area ◽  
Longitudinal Vibrations ◽  
Cross Sectional ◽  
Method Error ◽  
Various Boundary Conditions ◽  
Elastic Fixation ◽  
Crosssectional Area

The paper presents solutions to the direct and inverse problems on longitudinal vibrations of a rod with a variable cross-sectional area. The law of variation of the cross-sectional area is modeled as an exponential function of a polynomial of degree n . The method for reconstructing this function is based on representing the fundamental system of solutions of the direct problem in the form of a Maclaurin series in the variables x and λ. Examples of solutions for various section functions and various boundary conditions are given. It is shown that to recover n unknown coefficients of a polynomial, n eigenvalues are required, and the solution is dual. An unambiguous solution was obtained only for the case of elastic fixation at one of the rod’s ends. The numerical estimation of the method error was made using input data noise. It is shown that the error in finding the variable crosssectional area is less than 1% with the error in the eigenvalues of longitudinal vibrations not exceeding 0.0001.

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