Structure of Needle Mesophyll in the Genus <i>Larix</i> Species (Pinaceae)

Abstract

The structure of needle mesophyll and the forms of assimilative cells in the genus Larix species are discussed on the example of L. gmelini var. gmelini, L. decidua, L. kaempferi and L. sibirica. Needle samples were fixed in the Gammalund’s mixture. The study of the mesophyll was carried out on transverse, paradermal and radial sections of the middle part of the needles using a light microscope. To clarify the shape of chlorenchyma cells, macerated preparations were used. It is shown that the needle mesophyll in Larix species mainly consists of large cells of complex shape, which touch their convex parts or ends to form a well-developed system of intercellular spaces, which may comtribute to intense gas exchange. Different variants of flat folded, flat cellular and more complicated folded-cellular assimilative cells are described. The flat folded cells are characterized by a variety of lobed configurations on transverse sections and elongated oval projections on radial sections. The flat cellular cells are found on needle longitudinal sections of and consist of cellular links facing both perpendicular (cellular cells of the first group) and parallel (cellular cells of the second group) to the leaf surface. The folded-cellular cells combine transverse folded contours and longitudinal cellular outlines. In the needle mesophyll of the studied Larix species, weak differentiation into palisade and spongy parenchyma is observed; the cells of the middle part (median cells) are additionally distinguished between them. The palisade tissue is formed mainly by cellular cells of the first group, the spongy tissue by cellular cells of the second group. The median cells are located on both sides of the vascular bundle along a large needle radius; they can be either flat and slightly folded, or folded-cellular. The studied Larix species are similar in th esize of assimilative cells and the structure of the needle mesophyll; the main differences between them are related to the features of cell dissection both in transverse and longitudinal directions.