DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Scots pine (Pinus sylvestris) old stem. Light micrograph of a section through a stem from a Scots pine tree, showing remains of the epidermis and cuticle, with the cork cambium and developing cork (brown), phellogen and phelloderm. From outside in: cortex of parenchyma cells, consisting of scattered large resin canals (red) and small resin canals (blue); ring of secondary phloem composed of sieve tube cells (blue-black) and albuminous cells; under the phloem is a ring of vascular cambium; secondary xylem (brown), composed large tracheid cells and parenchyma cells; primary xylem, consisting of metaxylem and protoxylem; pith (centre) composed of parenchyma cells; principal and subsidiary medullary rays (blue). The annual growth rings of autumn wood (small.
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