The structue of phloem growth rings was studied in relation to their width in 10 apparently healthy European silver firs (Abies alba Mill.) from Ravnik, Slovenia. The relation between phloem and xylem increment and variation in number of phloem and xylem cells within different radial rows of the same ring were researched. Further, the relation between the phloem and xylem growth rings formed in the same year, and the corresponding number of cells in dormant cambium zone were investigated. The tissues were taken from living trees using the method of intact tissue sampling. The investigations were done with a light microscope on permanently imbedded cross-sections, stained with safranin and astra blue. The results show that the structure of the phloem growth ring depends on its width. The phloem increment comprised 5 to 11 sieveve cells, mostly with 3 to 4 layers wide early phloem. More or less continous tangential band of axial parenchyma usually separated the early and the late phloem. The late phloem was generally 1 to 3 cells wide. Wider phloem rings (8,9 and 11 cell layers) some times contained an additional discontinuous tangential band of axial parenchyma. Narrow phloem rings (5 to 6 cell layers wide) contained more early than late phloem, whereas wider rings (11 cell layers) contained more late phloem. The cambium produced more xyxlem than phloem cells. The xylem rings were 2 to 21 times wider than the corresponding phloem ones. The xylem rings were 8 to 177 cells wide. The differences in the number of cells within different radial rows of the same rings comprised up to 103 cells in xylem rings, and up to 4 cells in phloem rings. The dormant cambium zone contained 5 to 11 cell layers. When the cambium zone was narrow (5 to 6 cell layers wide) the xylem and phloem rings were narrow as well. When the cambium zone was wide (9, 10 or 11 cell layers) the xylem and phloem rings were also wide.
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