DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
The cut surface of the trunk of a newly felled European yew tree, Taxus baccata. The picture shows the heartwood (red hues) and to right, detaching layers of bark. The sapwood is a thin layer between the bark and the heartwood, and is not distinct here. The heartwood shows annual growth rings. A characteristic growth pattern of yew is the development with age of bulges along the trunk; these correspond to the waviness of the growth rings top right. The vivid red colour is caused by the presence of naphthoquinones, and is particularly striking on freshly cut timber; it fades with storage to an orange/brown hue.All parts of the tree are poisonous except the red aril that surrounds the seeds. T. baccata leaves are the source of 10-deacetylbaccatin, a precursor of the anticancer agent paclitaxel ("Taxol"). Paclitaxel stabilises microtubules within cells; this stops cell division (mitosis).
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