As we approach his London house Thomas Pakenham introduces me to a handsome tree. “Do you know the loquat? Sometimes called the Chinese medlar. Yellow, quince-like fruits.” Trees are Pakenham’s passion, the subject of his scholarly books, the object of his dedicated travelling. At Tullynally Castle in Ireland, the vast stately pile he inherited from his uncle, he has 1,600 acres and has planted 90,000 trees. In London he has a small patio, featuring gigantic hydrangeas, a tree-sized Fatsia japonica and a climber called Akebia, bearing chocolate-scented fruits. After my visit he will go to the local church and deliver