An artists impression ofan environment where prehistoric plants thrivedChristian Jegou/Science Photo LibraryWhen the Earth Was GreenRiley Black (St Martins Press (US, available now; UK, later this month))The behaviour of plants is invisible to the naked human eye. They operate on timescales our imaginations cant entertain, and they run roughshod over familiar categories of self, other and community. I confess that I find them boring.Luckily, others dont Riley Black, a palaeontologist and an occasional New Scientist contributor, for one. Wandering among (or is it through?) a 14,000-year-old aspen clone, a single organism made