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As biodiversity declines, locating and conserving the planet’s plant life is becoming more important. The Millennium seed bank in Wakehurst, West Sussex, has been doing just that for 25 years, collecting and storing seeds and keeping them in trust for countries all over the world should they ever be needed. To mark the anniversary, Patrick Greenfield took a tour of the site. He tells Madeleine Finlay about the journey a seed takes from arrival to cold storage, and how some are already helping to return endangered plant species to the wild. Help support our independent journalism at theguardian.com/sciencepod