A koala up a gumtree is the classic image of the Australian bush. How that odd partnership evolved is one of the strands woven into this episode of Nature Of Australia. The program tells the story of how the island continent's wooded margins came to be dominated by one unique type of tree growing in a great variety of forms - the eucalypt. The nursery for nearly all life in Australia is the rainforest, of which only a few patches remain today - th last remnants of vast, dense forests that covered Australia when it first broke away from the ancestral super-continent of Gondwana, and voyaged north into isolation. From among its proliferation of plants emerged the eucalypts, the characteristic gum trees - and from among the forest animals arose a great and varied company of marsupials, adapting to every kind of environment that evolved in response to Australia's changing, drying climate.