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PubMed2006

Effect of girdling above the abscission zone of fruit on 'Bartlett' pear ripening on the tree.

Pear fruit usually soften and develop a melting texture when harvested at the mature green stage and ripened. The reason why the fruit does not fully ripen on the tree is unknown. To clarify this, our attention was directed to the continuous supply of assimilates and/or other substances into the fruit via phloem transport. To determine the effect of inhibiting phloem transport on fruit ripening on the tree, a girdling treatment was applied to the branch above the abscission zone of 'Bartlett' pear (Pyrus communis L.). Girdling significantly enhanced the ethylene production of fruit on day 12 compared with control fruit. Fruit softening was also stimulated by girdling. On day 8, flesh firmness was similar in treated fruit on the tree and in fruit off the tree, and was significantly lower than that of untreated fruit on the tree. The patterns of transcript accumulation for the ethylene biosynthetic [1-aminocyclopropane-1-carboxylate (ACC) synthase (PcACS) and ACC oxidase (PcACO)] and polygalacturonase (PcPG1 and PcPG3) genes showed good correspondence with ethylene production and fruit softening, respectively. Thus, fruit ripening on the tree was stimulated via ethylene by girdling on the branch above the abscission zone of fruit to interrupt phloem transport. Assimilates and/or other substances in phloem sap may prevent fruit ripening on the tree.

Agriculture↗

PubMed1999

Multiple local maxima for likelihoods of phylogenetic trees: a simulation study.

Steel demonstrated that the maximum-likelihood function for a phylogenetic tree may have multiple local maxima. If this phenomenon were general, it would compromise the applicability of maximum likelihood as an optimality criterion for phylogenetic trees. In several simulation studies reported on in this paper, the true tree, and other trees of very high likelihood, rarely had multiple maxima. Our results thus provide reassurance that the value of maximum likelihood as a tree selection criterion is not compromised by the presence of multiple local maxima--the best estimates of the true tree are not likely to have them. This result holds true even when an incorrect nucleotide substitution model is used for tree selection.

Base Sequence↗

PubMed1988

Relative efficiencies of the maximum parsimony and distance-matrix methods in obtaining the correct phylogenetic tree.

The relative efficiencies of the maximum parsimony (MP) and distance-matrix methods in obtaining the correct tree (topology) were studied by using computer simulation. The distance-matrix methods examined are the neighbor-joining, distance-Wagner, Tateno et al. modified Farris, Faith, and Li methods. In the computer simulation, six or eight DNA sequences were assumed to evolve following a given model tree, and the evolutionary changes of the sequences were followed. Both constant and varying rates of nucleotide substitution were considered. From the sequences thus obtained, phylogenetic trees were constructed using the six tree-making methods and compared with the model (true) tree. This process was repeated 300 times for each different set of parameters. The results obtained indicate that when the number of nucleotide substitutions per site is small and a relatively small number of nucleotides are used, the probability of obtaining the correct topology (P1) is generally lower in the MP method than in the distance-matrix methods. The P1 value for the MP method increases with increasing number of nucleotides but is still generally lower than the value for the NJ or DW method. Essentially the same conclusion was obtained whether or not the rate of nucleotide substitution was constant or whether or not a transition bias in nucleotide substitution existed. The relatively poor performance of the MP method for these cases is due to the fact that information from singular sites is not used in this method. The MP method also showed a relatively low P1 value when the model of varying rate of nucleotide substitution was used and the number of substitutions per site was large. However, the MP method often produced cases in which the correct tree was one of several equally parsimonious trees. When these cases were included in the class of "success," the MP method performed better than the other methods, provided that the number of nucleotide substitutions per site was small.

Biological Evolution↗

PubMed1995

Effects of thinning on soil and tree water relations, transpiration and growth in an oak forest (Quercus petraea (Matt.) Liebl.).

To quantify the effects of crown thinning on the water balance and growth of the stand and to analyze the ecophysiological modifications induced by canopy opening on individual tree water relations, we conducted a thinning experiment in a 43-year-old Quercus petraea stand by removing trees from the upper canopy level. Soil water content, rainfall interception, sap flow, leaf water potential and stomatal conductance were monitored for two seasons following thinning. Seasonal time courses of leaf area index (LAI) and girth increment were also measured. Predawn leaf water potential was significantly higher in trees in the thinned stand than in the closed stand, as a consequence of higher relative extractable water in the soil. The improvement in water availability in the thinned stand resulted from decreases in both interception and transpiration. From Year 1 to Year 2, an increase in transpiration was observed in the thinned stand without any modification in LAI, whereas changes in transpiration in the closed stand were accompanied by variations in LAI. The different behaviors of the closed and open canopies were interpreted in terms of coupling to the atmosphere. Thinning increased inter-tree variability in sap flow density, which was closely related to a leaf area competition index. Stomatal conductance varied little inside the crown and differences in stomatal conductance between the treatments appeared only during a water shortage and affected mainly the closed stand. Thinning enhanced tree growth as a result of a longer growing period due to the absence of summer drought and higher rates of growth. Suppressed and dominant trees benefited more from thinning than trees in the codominant classes.

Journal Article↗

PubMedDate not supplied

Water use by Pinus radiata trees in a plantation.

We used the heat-pulse velocity technique to estimate transpirational water use of trees in an experimental 16-year-old Pinus radiata D. Don plantation in South Australia during a 4-month period from November 1993 to March 1994 (spring-summer). Fertilization and other silvicultural treatments during the first 8 years of the plantation produced trees ranging in diameter at a height of 1.3 m from 0.251 to 0.436 m, with leaf areas ranging from 83 to 337 m(2). Daily water use was greater for large trees than for small trees, but transpiration per unit leaf area was nearly identical. Daily transpiration was highly correlated with available soil water in the upper 1 m of soil and weakly correlated with irradiance and air temperature. For the stand (0.4 ha), estimated rates of transpiration ranged from 6.8 to 1.4 mm day(-1) in wet and dry soil conditions, respectively. Total water use by the plantation during the 4-month study period was 346 mm. Water transpired by the trees was about three times that extracted from the upper 1 m of soil. Large trees extracted water from the same soil volume as small trees and did not exhibit a greater potential to extract water from deeper soil when the upper horizons become dry.

Journal Article↗

PubMed1996

Carbon partitioning and allocation in northern red oak seedlings and mature trees in response to ozone.

Northern red oak (Quercus rubra L.) seedlings and trees differ in their response to ozone. Previous work reported reductions in net photosynthesis, carboxylation efficiency and quantum yield of mature tree leaves, whereas seedling processes were unaffected by the same ozone exposure. To further characterize differences in ozone response between seedlings and mature trees, we examined carbon partitioning and allocation in 32-year-old trees and 4-year-old seedlings of northern red oak after exposure to subambient (seasonal SUM00 dose (sum of all hourly ozone exposures) = 31 ppm-h), ambient (SUM00 dose = 85 ppm-h) and twice ambient (SUM00 dose = 151 ppm-h) ozone concentrations for three growing seasons. For mature trees, ozone exposure decreased foliar starch partitioning, increased starch partitioning in branches and increased (14)C retention in leaves. In contrast, starch partitioning in leaves and branches, and foliar (14)C retention in seedlings were unaffected by ozone exposure, but soluble carbohydrate concentrations in coarse and fine roots of seedlings were reduced. Differences in carbohydrate demand between seedlings and mature trees may underlie the higher leaf ozone uptake rates and greater physiological response to ozone in mature northern red oak trees compared with seedlings.

Journal Article↗

PubMedDate not supplied

Seasonal root distribution and soil surface carbon fluxes for one-year-old Pinus radiata trees growing at ambient and elevated carbon dioxide concentration.

The increase in number of fine (< 0.5 mm diameter) roots of one-year-old clonal Pinus radiata D. Don trees grown in large open-top field chambers at ambient (362 micro mol mol(-1)) or elevated (654 micro mol mol(-1)) CO(2) concentration was estimated using minirhizotron tubes placed horizontally at a depth of 0.3 m. The trees were well supplied with water and nutrients. Destructive harvesting of roots along an additional tube showed that there was a linear relationship between root number estimated from the minirhizotron and both root length density, L(v), and root carbon density, C(v), in the surrounding soil. Root distribution decreased with horizontal distance from the tree. At a depth of 0.3 m, 88% of the total C(v) was concentrated within a 0.15-m radius from tree stems in the elevated CO(2) treatment, compared with 35% for trees in the ambient CO(2) treatment. Mean C(v) along the tubes ranged up to 5 x 10(-2) micro g mm(-3) and tended to be greater for trees grown at elevated CO(2) concentration, although the differences between CO(2) treatments were not significant. Root growth started in spring and continued until late summer. There was no significant difference in seasonal rates of increase in C(v) between treatments, but roots were observed four weeks earlier in the elevated CO(2) treatment. No root turnover occurred at a depth of 0.3 m during the first year after planting. Mean values of carbon dioxide flux density at the soil surface, F, increased from 0.02 to 0.13 g m(-2) h(-1) during the year, and F was 30% greater for trees grown at elevated CO(2) concentration than at ambient CO(2). Diurnal changes in F were related to air temperature. The seasonal increase in F continued through the summer and early autumn, well after air temperature had begun to decline, suggesting that the increase was partly caused by increase in C(v) as the roots colonized the soil profile.

Journal Article↗

PubMed1996

Radial distributions of Pb in stems of young Norway spruce trees grown in Pb-contaminated soil.

Concentrations of Pb in individual stem xylem rings of 5-year-old Norway spruce trees (Picea abies (L.) Karst.) were determined after one growing season in soil containing a low, medium or high concentration of Pb. In trees in the control and low-Pb soil treatments, Pb concentrations increased from the outer annual rings toward the stem center, whereas in trees grown in the soil treatment containing a medium Pb concentration, all of the four tree rings analyzed contained similar concentrations of Pb. Although trees grown in the high-Pb soil treatment had higher concentrations of Pb in the outer annual rings than both control trees and trees in the low-Pb soil treatment, the highest concentrations of Pb were never observed in the outermost rings, which were formed during the period of exposure to increased soil Pb. We conclude that radial distribution patterns of Pb in Norway spruce stems do not directly reflect changes in soil Pb concentration but depend on several internal, physiological factors and, therefore, do not provide reliable information about past variations in Pb contamination of soil.

Journal Article↗

PubMed1998

A model of dry matter partitioning in trees.

In mechanistic growth models, the description of assimilate allocation or dry matter partitioning plays a key role. Although theoretical concepts of allocation exist, they include many parameters that cannot be quantified. Therefore, many growth models use descriptive keys that represent the proportions of dry matter or carbohydrates assigned to each plant component. I have developed a model to describe the dynamic partitioning of dry matter in individual trees, and used it to investigate the effects of growth conditions on the partitioning pattern in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and beech (Fagus sylvatica L.). The model estimates the fractions of total available dry matter that should go to certain plant parts, based on the concept of structural balances. Both mechanistic and allometric relationships between tree components are used to model conditions for the dynamic distribution of dry matter. The model was to used to estimate the effects of dominance position, site conditions, and thinning on growth partitioning. The fractions of the annual current increment of total dry matter gradually changed with tree age, but the changes were relatively small, especially after age 20. Compared with beech, Douglas-fir invested more dry matter in foliage, especially at the cost of the branch and stem components. Trees of average basal area invested more dry matter in branches and less in stem than suppressed trees, and their estimated increase in stem diameter over time generally fitted the yield table data well. Stem diameter development was underestimated at higher ages only in the case of a Douglas-fir tree of average basal area on a poor site. Over time, the proportion of standing biomass in foliage and fine root fractions showed a gradual decline, whereas there was a gradual increase in the proportion of standing biomass in the stem fraction. These age-related changes were attributed to different loss rates among components. Analysis of the effects of thinning revealed that a discontinuous reduction in stem number results in a slow decrease in partitioning to the stem. The most obvious response to thinning consisted in a sharp decrease in partitioning to fine roots and foliage, and an increased investment in branches. Stem diameter growth appeared relatively constant in response to thinning, indicating that it will increase almost linearly with time. I conclude that the model is able to reproduce the development of an individual tree over time, both in terms of stem diameter and biomass. The model is thus suitable for simulating the effects of competition for resources on growth and development of forest stands.

Journal Article↗

PubMed2000

Carbon isotope discrimination and oxygen isotope composition in clones of the F(1) hybrid between slash pine and Caribbean pine in relation to tree growth, water-use efficiency and foliar nutrient concentration.

The objectives of this study were: (1) to examine how foliar carbon isotope discrimination (Delta) and oxygen isotope composition (delta(18)O) are related to tree growth, ash mineral nutrient concentration and foliar nutrient concentration in 7-year-old clones of the F(1) hybrid between slash pine (Pinus elliottii Engelm.) and Caribbean pine (P. caribaea var. hondurensis Barr. et Golf.) in subtropical Australia; and (2) to evaluate the potential of using foliar Delta, ash mineral nutrient concentration and delta(18)O measurements for selecting F(1) hybrid pine clones with high water-use efficiency (WUE) and growth potential. There were significant differences in tree growth, foliar Delta, delta(18)O and ash mineral nutrient concentration among the eight clones tested. Significant negative linear relationships existed between tree growth and Delta, extrapolating to zero growth at Delta = 24-30 per thousand. There were strong genetic correlations (r = -0.83 to -0.96) between Delta and tree growth, particularly tree height. Significant non-genetic correlations (r = -0.62 to -0.80) existed between Delta and foliar K concentration. Foliar delta(18)O, ash mineral nutrient concentration and foliar nutrient concentration were unrelated to tree growth. In the F(1) hybrid pine clones, variation in tree WUE, as reflected by Delta, was largely attributed to a genetic effect on leaf photosynthetic capacity rather than on stomatal conductance, as reflected by foliar delta(18)O.

Journal Article↗

PubMed2002

Changes in whole-tree water relations during ontogeny of Pinus flexilis and Pinus ponderosa in a high-elevation meadow.

We measured sap flux in Pinus ponderosa Laws. and Pinus flexilis James trees in a high-elevation meadow in northern Arizona that has been invaded by conifers over the last 150 years. Sap flux and environmental data were collected from July 1 to September 1, 2000, and used to estimate leaf specific transpiration rate (El), canopy conductance (Gc) and whole-plant hydraulic conductance (Kh). Leaf area to sapwood area ratio (LA/SA) increased with increasing tree size in P. flexilis, but decreased with increasing tree size in P. ponderosa. Both Gc and Kh decreased with increasing tree size in P. flexilis, and showed no clear trends with tree size in P. ponderosa. For both species, Gc was lower in the summer dry season than in the summer rainy season, but El did not change between wet and dry summer seasons. Midday water potential (Psi(mid)) did not change across seasons for either species, whereas predawn water potential (Psi(pre)) tracked variation in soil water content across seasons. Pinus flexilis showed greater stomatal response to vapor pressure deficit (VPD) and maintained higher Psi(mid) than P. ponderosa. Both species showed greater sensitivity to VPD at high photosynthetically active radiation (PAR; > 2500 micromol m-2 s-1) than at low PAR (< 2500 micromol m-2 s-1). We conclude that the direction of change in Gc and Kh with increasing tree size differed between co-occurring Pinus species, and was influenced by changes in LA/SA. Whole-tree water use and El were similar between wet and dry summer seasons, possibly because of tight stomatal control over water loss.

Altitude↗

PubMed2002

Stomatal conductance alone does not explain the decline in foliar photosynthetic rates with increasing tree age and size in Picea abies and Pinus sylvestris.

Foliar light-saturated net assimilation rates (A) generally decrease with increasing tree height (H) and tree age (Y), but it is unclear whether the decline in A is attributable to size- and age-related modifications in foliage morphology (needle dry mass per unit projected area; M(A)), nitrogen concentration, stomatal conductance to water vapor (G), or biochemical foliage potentials for photosynthesis (maximum carboxylase activity of Rubisco; V(cmax)). I studied the influences of H and Y on foliage structure and function in a data set consisting of 114 published studies reporting observations on more than 200 specimens of various height and age of Picea abies (L.) Karst. and Pinus sylvestris L. In this data set, foliar nitrogen concentrations were independent of H and Y, but net assimilation rates per unit needle dry mass (A(M)) decreased strongly with increasing H and Y. Although M(A) scaled positively with H and Y, net assimilation rates per unit area (A(A) = M(A) x A(M)) were strongly and negatively related to H, indicating that the structural adjustment of needles did not compensate for the decline in mass-based needle photosynthetic rates. A relevant determinant of tree height- and age-dependent modifications of A was the decrease in G. This led to lower needle intercellular CO2 concentrations and thereby to lower efficiency with which the biochemical photosynthetic apparatus functioned. However, V(cmax) per unit needle dry mass and area strongly decreased with increasing H, indicating that foliar photosynthetic potentials were lower in larger trees at a common intercellular CO2 concentration. Given the constancy of foliar nitrogen concentrations, but the large decline in apparent V(cmax) with tree size and age, I hypothesize that the decline in Vcmax results from increasing diffusive resistances between the needle intercellular air space and carboxylation sites in chloroplasts. Increased diffusive limitations may be the inevitable consequence of morphological adaptation (changes in M(A) and needle density) to greater water stress in needles of larger trees. Foliage structural and physiological variables were nonlinearly related to H and Y, possibly because of hyperbolic decreases in shoot hydraulic conductances with increasing tree height and age. Although H and Y were correlated, foliar characteristics were generally more strongly related to H than to Y, suggesting that increases in height rather than age are responsible for declines in foliar net assimilation capacities.

Biomass↗

PubMed2006

Translocation of nitrogen in the xylem of field-grown cherry and poplar trees during remobilization.

Studies of small trees growing in pots have established that individual amino acids or amides are translocated in the xylem sap of a range of tree species following bud burst, as a consequence of nitrogen (N) remobilization from storage. This paper reports the first study of N translocation in the xylem of large, deciduous, field-grown trees during N remobilization in the spring. We applied 15N fertilizer to the soil around 10-year-old Prunus avium L. and Populus trichocharpa Torr. & Gray ex Hook var. Hastata (Dode) A. Henry x Populus balsamifera L. var. Michauxii (Dode) Farwell trees before bud burst to label N taken up by the roots. Recovery of unlabeled N in xylem sap and leaves was used to demonstrate that P. avium remobilizes N in both glutamine (Gln) and asparagine (Asn). Sap concentrations of both amides rose sharply after bud burst, peaking 14 days after bud burst for Gln, and remaining high some 45 days for Asn. There was no 15N enrichment of either amide until 21 days after bud burst. In the Populus trees, nearly all the N was translocated in the sap as Gln, the concentration of which peaked and then declined before the amide was enriched with 15N, 40 days after bud burst. Xylem sap of clonal P. avium trees was sampled at different positions in the crown to assess if the amino acid and amide composition of the sap varied within the crown. Sap was sampled during remobilization (when the concentration of Gln was maximal), at the end of remobilization and at the end of the experiment (68 days after bud burst). Although the date of sampling had a highly significant effect on sap composition, the effect of position of sampling was marginal. The results are discussed in relation to N translocation in adult trees and the possibility of measuring N remobilization by calculating the flux of N translocation in the xylem.

Amides↗

PubMed1989

Solar equivalent leaf area: an efficient biometrical parameter of individual leaves, trees and stands.

The solar equivalent leaf area (A(s)), a simply and easily determined biometrical parameter of leaves, trees and stands, was derived theoretically. The parameter is defined as projected leaf area weighted for the time integral of irradiance at a given location in the canopy relative to that of fully irradiated leaves at the top of the canopy. The efficiency of A(s) as a basis for estimating stand-area transpiration of a mature oak (Quercus robur L.) forest from measurements of transpiration by individual trees was compared with that of other stand and tree characteristics. Stand transpiration estimates based on A(s) were more precise and less prone to systematic error than estimates based on basal area, timber volume, projected tree crown area, projected leaf area, or leaf dry mass. Solar equivalent leaf area reflects both the amount and the physiological properties of leaves and can be used as a measure of tree size and functional capacity. It can be calculated from ordinary forest inventory data on trees and stands, adjusted according to simple phyllometric data. It appears to have wide application in ecological and forestry studies for relating the physiological characteristics of individual leaves to those of entire trees or stands.

Journal Article↗

PubMed1991

Root respiration in Chamaecyparis obtusa trees.

We examined the respiration rate of root segments, which had a constant length in relation to their diameter, from three small and two large 26-year-old Chamaecyparis obtusa (Siebold & Zucc.) Endl. trees. The dependence of respiration rate on segment diameter was described by a power function with an exponent of about 1.5, except for the smallest sample tree, for which the exponent was 1.74. Unlike stem segments, root segments of similar diameter showed similar rates of respiration regardless of the tree from which the root segments had been taken. On the basis of the power function, we propose a new equation to estimate the total root respiration rate of a tree. The relationship between root respiration rate per tree and root weight can be expressed by a power function with an exponent of 1.11. The ratio of the specific respiration rate of stems to that of roots was 0.7 for the three smaller trees, and 1.1 to 1.3 for the two larger trees. In November, the stand respiration rate of roots was estimated to be 0.36 kg CO(2) ha(-1) h(-1) for a root biomass (dry weight) of 28 Mg ha(-1).

Journal Article↗

PubMed2003

New glaucoma classification method based on standard Heidelberg Retina Tomograph parameters by bagging classification trees.

PURPOSE: In this article we propose and evaluate nonparametric tree classifiers that can handle non-normal data and a large number of possible predictors using the full set of standard Heidelberg Retina Tomograph measurements for classifying glaucoma. METHODS: The classifiers were trained and tested using standard Heidelberg Retina Tomograph parameters from examinations of 98 subjects with glaucoma and 98 normal subjects of the Erlangen Glaucoma Registry. All patients and control subjects were evaluated by 15 degrees -optic disc stereographs, Heidelberg Retina Tomograph measurements, standard computerized white-in-white perimetry, and 24-hour-intraocular pressure profiles. The subjects were matched by age and sex. Standard classification trees as well as bagged classification trees were used. The classification outcome of the trees was compared with the classification by two published linear discriminant functions based on Heidelberg Retina Tomograph variables with respect to their cross-validated misclassification error. RESULTS: The bagged classification tree had the lowest misclassification error estimate of 14.8% with a sensitivity of 81.6% at a specificity of 88.8%. The cross-validated error rates of the two linear discriminant function procedures were 20.4% (sensitivity 82.6%, specificity 76.7%) and 20.6% (sensitivity 81.4%, specificity 77.3%) for our set of observations. Bagged classification trees were able to reduce the misclassification error of glaucoma classification. CONCLUSIONS: Bagged classification trees promise to be a new and efficient approach for glaucoma classification using morphometric 2- and 3-dimensional data derived from the Heidelberg Retina Tomograph, taking into account all given variables.

Case-Control Studies↗

PubMed1984

Vertex analysis of Purkinje cell dendritic trees in the cerebellum of the rat.

All networks are made up of vertices (points interconnected by segments), which include terminals interconnected by terminal segments, nodes interconnected by link segments and the root point connected to the tree by the root segment. All nodes may be classified into unique types according to the number of terminal and link segments they drain. For example, there are three distinct dichotomous nodes, a 'primary' node draining two terminal segments, a 'secondary' node draining one terminal segment and a link segment, and a 'tertiary' node draining two link segments. The numbers of primary and tertiary nodes approximate to equality in large networks and thus the ratio of primary to secondary nodes defines topology. All higher order nodes ( trichotomous and beyond) may be resolved into dichotomous forms and incorporated into the analysis. Different forms of growth may thus be analysed by comparing the frequency distributions of nodes with those generated by computer simulated growth models. Moreover, all vertices can be ordered so that metrical parameters are easily incorporated and the hierarchical arrangements of vertices of different order discerned. The dendritic trees of 48 Purkinje cells, taken from folia along the primary fissure, were analysed using vertex analysis. The mean number of segments in Purkinje cell trees was 881 +/- 23 (s.e.) and mean total dendritic length 7959 +/- 233 (s.e.) micrometers. Segment lengths were longest over proximal segments but over most of the tree segment lengths were constant at 10 +/- 0.2 (s.e.) micrometers. Vertex, segment and terminal frequency distributions of equivalent orders were all normal with a slight positive skew. Peak frequencies were recorded at the 12th equivalent order. The mean primary/secondary nodal vertex ratio was 0.93 and the proportion of trichotomous branch points in the tree was 5%. Comparison of the frequency distribution of all vertices with computer generated models showed that growth of the Purkinje cell was most closely simulated by a random terminal growth model, incorporating 5% trichotomy , in which the branching of high order terminals was more likely than low order terminals. It was concluded that growth of the Purkinje cell tree could proceed by random terminal branching with growth occurring preferentially over a front composed of terminals that are ascending through a corridor in the molecular layer whose margins are defined by neighbouring trees.

Animals↗

PubMed2002

Retinal vascular tree morphology: a semi-automatic quantification.

A semi-automatic method to measure and quantify geometrical and topological properties of continuous vascular trees in clinical fundus images is described. Measurements are made from binary images obtained with a previously described segmentation process. The skeletons of the segmented trees are produced by thinning,ff branch and crossing points are identified and segments of the trees are labeled and stored as a chain code. The operator selects a tree to be measured and decides if it is an arterial or venous tree. An automatic process then measures the lengths, areas and angles of the individual segments of the tree. Geometrical data and the connectivity information between branches from continuous retinal vessel trees are tabulated. A number of geometrical properties and topological indexes are derived. Vessel diameters and branching angles are validated against manual measurements and several derived geometrical and topological properties are extracted from red-free fundus images of ten normotensive and ten age- and sex-matched hypertensive subjects and compared with previously reported results.

Adult↗