Prince Charles yesterday opened the Millennium Seed Bank, which is intended to protect more than 24,000 plant species around the world from extinction. The $114 million seed bank in southern England — the largest such effort so far — will store millions of seeds in underground bomb-proof, flood-proof vaults, and house specimens of more than one-tenth of the world’s flora. If necessary, the seeds will be used to reintroduce species into the wild. But the prince called on the international community to take steps to preserve plant species in their natural settings, so that the reserves in the “Bank of England of the botanical world” will never have to be tapped.