bild

White bryony stem. Light micrograph of a transverse section through the stem of a white bryony (Bryonia alba) plant, showing a single collateral vascular bundle. The bundle has an outer and inner phloem (blue) with large sieve tubes, some of which show sieve plates and companion cells, and an inner xylem (crimson) with large vessels and small woody parenchyma tissue. The cambium (small, light blue cells) is in-between the phloem and xylem. Surrounding the vascular bundle is the ground tissue parenchyma. Magnification: x37 when printed 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR KEITH WHEELER/SCIENCE PHOTO LIBRARY)