DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Lenticels on the bark of the Himalayan White Birch, Betula Jacquemontii. The picture is a close up view of a strip of bark shed from the trunk of a B. jacquemontii tree. The width of the frame is 4cm. The white background is the outer surface of the paper-like bark; the orange/brown horizontal areas of a granular appearance are the outside surface of the lenticels. On the tree, as here, they are horizontal ("transverse"). Their different sizes reflect their age; they extend as the girth of the tree enlarges. Bark is impermeable to the air; lenticels are porous structures that allow gaseous exchange between the living tissues beneath the bark and the atmosphere outside. Lenticels are found on the stems and roots of woody plants; they also occur on fruits such as apples, and on potatoes.B. jacquemontii is native to the Himalayas, valued in horticulture as an elegant specimen tree.
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