Scientists say that many of the world's plants are in danger of 1. drying / dying out – of becoming extinct. Dr Paul Smith, from Botanic Gardens Conservation International, said 2. one / once in five of the world's plants is in danger of 3. extinct / extinction. The world's botanic gardens 4. contents / contain about 100,000 species, including a 5. third / thirdly of all the world's endangered plants. Botanic gardens help to protect around 40 per cent of endangered 6. specials / species of plants. They contain many of the rarest plants. Dr Smith said: "This is the first 7. times / time that we have carried out a global assessment to look at the 8. width / wide range of plants grown, managed and 9. conserved / conversed in botanic gardens. For the first time we know what we have and, perhaps more 10. importance / importantly, what is missing from botanic gardens." Researcher Dr Samuel Brockington said the world's botanic gardens were the best 11. hoping / hope for saving the world's 12. most / must endangered plants. He said: "Currently, an estimated one-fifth of plant 13. diverse / diversity is under threat, yet there is no 14. technical / technique reason why any plant species should 15. become / becoming extinct." Dr Brockington warned that if we do not protect 16. engendered / endangered plants, people could have trouble finding food and fuel in the future. He said: "If 17. they / we do not conserve our plant diversity, humanity will struggle to 18. solution / solve the global challenges of food and fuel 19. security / secure…and climate change." Most of the plants are in danger because of humans cutting down forests for farming and cities, and because of 20. pests / pasts and climate change.