Abstract. Quantification is a major problem when using histology to study the influence of ecological factors on tree structure. This paper presents a method to prepare and to analyse transverse sections of cambial zone and of conductive phloem in bark samples. The following paper (II) presents the automated measurement procedure. Part I here describes and discusses the preparation method, and the influence of tree age on the observed structure. Highly contrasted images of samples extracted at breast height during dormancy were analysed with an automatic image analyser. Between three young (38 years) and three old (147 years) trees, age-related differences were identified by size and shape parameters, at both cell and tissue levels. In the cambial zone, older trees had larger and more rectangular fusiform initials. In the phloem, sieve tubes were also larger, but their shape did not change and the area for sap conduction was similar in both categories. Nevertheless, alterations were limited, and demanded statistical analysis to be identified and ascertained. The physiological implications of the structural changes are discussed.
Abstract. Image analysis provides the means to overcome quantification problems in plant science. Part I of this study (Vollenweider et al. 1994) presented a method of preparing transverse views of the cambial zone and conductive phloem in bark samples. Part II of the study presents computerized analysis of the images thus obtained. The equipment and procedures are described, and we show that presently available software can be sufficiently versatile and easily customized to perform automated histological measurements. The program allows the user considerable interactivity. The automated treatment requires particularly high quality standards in both sample preparation and image capture, but provides numerical results able to reveal fine histological differences.
The possibility of determining the combustion products (or accelerants) at the seat of a fire by the analysis of corresponding soot samples was investigated. Twenty liquid fuels (principally petroleum derivatives) and twelve plastic materials (from seven different polymer groups) were individually burned over one hour under controlled laboratory conditions. The soot produced was collected on glass plates and subsequently submitted to a sequence of physical and chemical analyses. Twelve casework samples (soot deposits on glass fragments collected at the fire scene) and five control samples (blind trials prepared in the laboratory) were submitted to the same analytical procedure. A total of 49 soot samples were considered. Macroscopic (35× magnification) and microscopic (TEM) studies were conducted on each soot sample. Digitized micrographs were processed in order to obtain certain physical parameters serving to characterize the size and form of the soot aggregates: perimeter, surface area, circularity and principal surface moments ratio. These data were transformed and used as variables for a discriminant analysis carried out with an SPSS program. Furthermore, the soot aggregates were characterized by their fractal dimension. The chemical composition of the soot samples was explored using three chromatographic methods: GC-FID, GC-MS, and pyrolysis-GC. Two studies were conducted: a comparison of the total chromatographic profiles obtained by GC-FID and pyrolysis-GC, and a comparison based upon qualitative and semi-quantitative analyses of 11 polycyclic aromatic hydrocarbons (PAH's) in order to determine the value of these compounds as potential markers for accelerants used at the start of a fire. The combination of physical and chemical parameters permitted the differentiation of most of the laboratory-prepared soot samples. The discriminating power was higher for the chemical analyses, with soot samples resulting from the combustion of plastic materials being the easiest to identify. Microscopy nevertheless provided interesting information concerning specific soot forms or elements. The combined results obtained by the analytical methods employed permitted the construction of a dichotomic table that can be used for the classification of soot samples taken from the scene of a fire. Additional research is required before such techniques can be routinely applied in casework.
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