The planet’s plant life lies in a vault with millions of seeds, a symbol of the vast, exuberant human diet. We’ll turn to it in the event of a disaster to rescue our crops, even though we’ve impoverished their biodiversity in recent decades: we’ve gone from some seven thousand varieties to thirty, of which rice, wheat and maize now account for more than half. And what have we done with the others? Deposited a backup before eradicating them from Earth? If the end the world is nigh, this Arcadia – with its inexhaustible collection of plants – may offer us one last chance to reinvent ourselves as a species.