STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Pine tree stem. Coloured light micrograph of a cross-section through the stem of a pine tree. The red wood (xylem, lower left) has resin canals in it, which are outlined in green. The resin produced by the canals contains turpentine, which stops bacteria, fungi and insects from decomposing or eating the stems or leaves. Several growth rings are also distinguishable in the xylem, which can be counted to calculate the tree's age, as the cambium (thin green ring at the edge) forms one ring each year as it expands outwards. The green feature spanning these rings is the phloem, which transports nutrients around the plant. The darker region at top is the cortex, the outer portion of the stem. Magnification: x18 when printed 10cm wide.
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