STUDY ON THE SECONDARY PHLOEM ANATOMY OF THE STEM OF 15 SPECIES IN PINUS

This paper deals with the structure of secondary phloem of stems in 14 species and 1 variety of Pinus ,and comparison of two subgenus(haploxylon,Diploxylon)and the different species. The main results are as follows; (1)The structure of secondary phloem is composed of an axial system and a radial system. The main constituents of the axial system are sieve cells, phloem parenchyma cells, crystalliferous cells and radial plates. The radial system is made up of uniseriate rays and fusiform rays containing horizontal resin canals. Compared with functioning phloem,the constituents of nonfunctioning phloem change greatly in form, structure and arrangement. (2)Some variations within various species have been shown in stratification of secondary phloem, phloem ray dilatation, resin canal density, crystalliferous cell frequency,quantity of ergastic substances in phloem parenchyma cell,phloem ray height, sieve cell length, radial and tangential width, sieve area diagram, height and radial width of upright ray cell, respectively. But no obvious regulation is found. (3) The differences are rather steady between two subgenus in shape and length of crystal, and number of epithelial cells around a resin canal in functioning phloem or phloem just losing its function,which can be served as the further evidence for separation of subgenus.