'Succulent' literally means 'juicy', which should give you a clue. ... Most big cacti are full of water - a big saguaro, for example, can hold many tonnes of water in its tissues.
But they wouldn't hold all that precious water for very long if they didn't protect it from dessication and from thirsty animals. So what methods of protection do you think they use? (When you've had a few ideas, ask me for the answers).
