Thomas Pakenham, 91, tells Harry Mount about his new book, The Tree Hunters. From the 17th century to the 19th century, British daredevils headed across the world to bring back seeds for arboretums back home. Among them was David Douglas, who brought back the Douglas Fir - and was gored to death by a wild bull in Hawaii in 1834. Thomas also recalls his own tree-hunting expeditions to bring back seeds from Tibet to his house, Tullynally, in County Westmeath, Ireland.