Stem Gallery

Dicotyledon plant stem, light micrograph

Dicotyledon plant stem. Light micrograph of a longitudinal radial section through a typical dicotyledon stem. The section has passed through a vascular bundle and other stem tissue (some of which have ring thickening, red). The tissue layers at right are mostly xylem and parenchyma. There is also a layer of cambium (light blue, centre). Several rows of phloem sieve tubes (yellow-green) are at centre left. At left are large parenchyma cells (blue) of the inner cortex of the stem. Magnification: x45 when printed at 10 centimetres high

© DR KEITH WHEELER/SCIENCE PHOTO LIBRARY

Lime tree stem, light micrograph

Lime tree stem. Light micrograph of a section through the stem of a lime tree (Tilia europaea). The outer epidermis has been shed and replaced by a layer of cork (dark red). Under the cork is the outer cortex layer of flexible collenchyma tissue (dark blue and red) and a lower cortex of parenchyma (blue). Next is a ring of phloem (blue) with large sieve tubes, companion cells and fibres (pink). The phloem is broken by primary medullary rays (blue, triangular) and thin subsidiary medullary rays (dark blue). Next is a ring of xylem (pink) with large files of vessels and small woody parenchyma (light blue). The primary xylem (dark blue) and the central pith of parenchyma tissue (light blue) are also shown. Magnification: x5 when printed 10 centimetres

© DR KEITH WHEELER/SCIENCE PHOTO LIBRARY

Pine stem, light micrograph

Pine stem. Light micrograph of a section through the stem of a pine (Pinus sp.) tree, showing xylem tissue. The xylem is made up of tracheid cells (light pink). There are thin files of parenchyma and tracheid cells (pale blue and red) of the subsidiary rays, which pass food substances radially. The large circular lacuna (resin duct, centre) is lined with parenchyma cells (light blue and red) that produce resin. The tracheid walls of many cells have bordered pits (green), which pass water and minerals side-ways between cells. Magnification: x132 when printed 10 centimetres wide

© DR KEITH WHEELER/SCIENCE PHOTO LIBRARY