Different trees have different sorts of hark, the variation is of two main kinds. The hark of an individual changes as it grows, and there are differences between mature trees of different species. The recognition of large trees in tropical forest depends on living as opposed to herbarium characters and amongst living characters baric is important. Botanists are slowly coming to realise that living characters are of importance to taxonomy and can supplement the characters visible on herbarium sheets but often hard to see in the forest (Corner 1940, Symington 1943, Henderson & Wyatt-Smith 1956). At present many living characters are used empirically if at all.