Observations of Bark Tissues of 12 Angiospermous Trees by Soft X-ray Photography

Abstract

Soft X-ray photography has been widely used in wood science and related fields, notably for constructing wood density profile. However, this useful method has not yet been popularly applied for examinations of bark structure. Therefore, we attempted to characterize the soft X-ray photographic images of barks for a total of 12 angiospermous tree species from Hokkaido, Japan. High contrast images were obtained, and the contrast reflected not only anatomical features but also maldistribution of calcium crystals. This means that soft X-ray photography is effective to visualize the accumulation of calcium crystals, which are ubiquitous across plant kingdom, in bark tissues. Optical microscopic observations further revealed that the sclerenchyma was exclusively associated by prismatic crystals even when other morphological types of calcium crystals were present. There is a possibility that the prismatic crystals serve some mechanical functions to supplement sclerenchyma in bark tissues.