Young aerial roots of common ivy, Hedera helix. The picture shows a stem from an ivy plant growing against a wall. The stem in the picture is not in contact with the wall, but is producing aerial roots on its shaded side (to right). The roots are positioned close to a leaf which is to the left and behind the stem. They are growing away from the direction of the light; an example of negative phototropism. Their function is attach the plant to its support, whether the bark of a tree or the wall of a house. When the roots touch a support, they penetrate any available crevices. Large crevices can accommodate whole roots; small crevices can be penetrated by fine hairy outgrowths from individual cells. This self-supporting mechanism enables the plant to grow to considerable height. This in turn results in exposure to higher light levels, allowing the production of flowers and seeds