The Green Planet

(soft orchestral music) -

Narrator

In the desert world, water thieves can come in many forms to exploit even the smallest chink in a plant's defense. (bird wings fluttering) One of the strangest travels within the gut of a fruit-eating mockingbird. (bird chirping) These are the seeds of Tristerix, a kind of mistletoe. Their goal is the water inside this hedgehog cactus. Using the spines as anchors, the seeds start to germinate. (suspenseful music) Each produces a long probe with which to try and locate the cactus's skin. For most, that's a stretch too far and they perish. But for this one, the cactus's surface is within reach. (suspenseful music) It clamped onto it with a special sucker and then waits for darkness. At night, the cactus opens its pores in order to respire. Oxygen goes out, carbon dioxide goes in, and so does Tristerix. Once within, its tissues spread throughout the body of the cactus, sustained by the precious store of water that they find there. Then a year later, it breaks through the cactus's skin and bursts into flower. (triumphant music) Hummingbirds come to drink their nectar and pollinate them as they do so. And then to complete the cycle Tristerix produces hundreds of white eye-catching seeds ready to be carried away by a bird to invade another cactus.