Epiphytes
In rain forests, the canopy produced by the upper layer of branches may be so dense that few plants can grow on the shady ground below. Even so, many plants have adapted to life in the rain forest, developing fascinating strategies for survival. For example, various species known as epiphytes use a host plant as a platform for growth. Although epiphytes grow on a host tree, they take no nutrients from the tree itself. Attached to the tree, sometimes 30 or 40 meters high, these aerial plants have access to sunlight but not to nutrients from the soil below. As a result, they have developed unusual mechanisms that have allowed them to overcome this problem.
听力材料：
Now listen to part of a lecture from a biology class.
(male professor) OK, so a good example of this type of plant, common to the rainforest, is the Urn plant. The Urn plant wraps its roots around the branches of the trees or sometimes around the trunk near the upper part of the tree. They use the tree for support and this allows them to reside high in the trees, in the canopy, where they can get plenty of sunlight.Now, the Urn plant has a unique shape. It got its name because of the formation of its leaves creates a kind of urn or bowl where it can store water. The Urn plant has rather long stiff spiky leaves. The leaves are slightly overlapping and are tightly rolled into a kind of cone shape or a funnel shape. Its flowers are held on a single stem in the center. Anyway, as I mentioned, the arrangement of the leaves forms a kind of receptacle or bowl at the base so that it is rainwater collects on the leaves it rolls down into the bowl where it can be stored.OK, so is unique shape helps it gather and store water. It also helps to gather other nutrients. This is because insects, dead leaves from other plants or other debris land on the leaves and then get washed down into the stored water. Gradually they decompose. The chemical break-down creates a nitrogen-rich food source in the stored water. So, the water supply contains a kind of liquid fertilizer that can be released to the plant whenever it needs the food.
Question：
Using the example of the Urn plant, explain how epiphytes have adapted to life in the rain forest.
