Cell Contents, Secretory Structures
When mentioning occurrence of crystals in woods of dicotyledons, wood anatomists usually specify degree of abundance, crystal shapes and sizes, and organo-graphic distribution. By “organographic distribution,” one means whether crystals are present in ray
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Cell Contents, Secretory Structures
7.1 Crystals 7.1.1 Observation and Description When mentioning occurrence of crystals in woods of dicotyledons, wood anatomists usually specify degree of abundance, crystal shapes and sizes, and Organographie distribution. By "organographic distribution," one means whether crystals are present in rays, axial parenchyma, or imperforate tracheary elements, whether they are in all cells or only part of them in any of those tissues, and whether crystals are equally distributed in all partsofaplant and whether crystals are equally distributed throughout a growth ring. W ood samples are often not adequate to provide all of the data one would ideally like in this respect. The chemical composition of crystals is often not specified. The assumption is made that unless there is a contrary indication, calcium oxalate is present. This assumption is justified in many but not all cases. Calcium oxalate survives most microtechnical treatments, and its lack of solubility in cantrast with that of other crystalline materials offers an inferential means of identification often used in practice although not often specified. An ideal means of identification of calcium oxalate is affered by energy dispersive X-ray analysis (EDXA), a method available as an attachment to a scanning electron microscope. Applications in study of woods are discussed by Gray and Cöte (1974) and Furuno and Cöte (1983). Thin coatings on walls ofparticular compounds can be detected, so that much more than crystals or other relatively obvious deposits can be studied. The precision ofEDXA results is admirable, although obviously it cannot serve für screening large quantities ofmaterial in brief periods of time. Crystals, particularly callcium oxalate crystals, are usually seen readily by means of the light microscope because of their refractiveness, although in some preparations they arenot obvious. The use of polarized light greatly enhances the visibility of crystals by presenting crystals bright against a dark background (Fig. 7.1.3, 7.7.5); iridescent patterns are sometimes formed (Fig. 7. 7.1), and sometimes entire crystals turn particular colors under polarized light (Fig. 7 .1.2- dark-appearing crystals are showing this phenomenon). Illustrations using partially polarized light (Fig. 7.1.2, 7.1.3) as opposed to fully polarized light (Fig. 7.1.1) can be recommended because the polarized light produces a bright appearance, highlighting the crystal, while still showing the background and thus revealing the context of the crystals better. Most of the illustrations in the present account do not use polarized light and thus simulate what the reader is likely to see upon scanning a slide without any special means.
S. Carlquist, Comparative Wood Anatomy © Springer-Verlag Berlin Heidelberg 1988
Crystals
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Fig. 7.1. Rhomboidal (prismatic) crystals in ray cells of radial sections, seen with polarized light
(1-3) and with SEM (4). 1 Fully polarized light, Scaevola spinescens (Goodeniaceae). 2 Partially
polarized light; some
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