DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Pine needle. Light micrograph of a transverse section through a leaf (needle) of a pine tree (Pinus sp.). The leaves are needle-like in order to present a large surface area for photosynthesis but prevent too much water loss (transpiration). They have an epidermis (orange) of thick walled cells covered with a thick layer of cuticle. The mesophyll layer (green) under the epidermis is made up of parenchyma cells with in-folded walls, in-between these are resin canals (white circles). The vascular cylinder (centre) is surrounded by the endodermis (blue) which regulates water and mineral movement. Under the endodermis are two vascular bundles made up of phloem sieve cells (blue) and xylem tracheids (red). Magnification: x46 when printed 10 centimetres wide.
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