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 crevices and dark places of the wall or tree over which the plant climbs. The trumpet creeper (Fig. 36), true or English ivy, and poison ivy climb by means of roots.

In some plants all the roots are aërial; that is, the plant grows above ground, and the roots gather food from the air. Such plants usually grow on trees. They are known as epiphytes or air-plants. The most familiar examples are some of the tropical orchids, which are grown in glass-houses (Fig. 37). Rootlike organs of dodder and other parasites are discussed in a future chapter.