Occasionally one finds a divided or compound leaf in such a position that one portion, because of being shaded above, receives the stronger light stimulus from the side, while the other portion is lighted from above. If this relation continues throughout the growth-period of the leaf the leaflets of one portion may lie in a different plane from those of the other portion. In such cases, some of the leaflets are permanently twisted to bring them into their proper light relation. V. Leaf Patterns. MOSAICS, OR CLOSE PATTERNS. [Illustration: Fig. 441. Fittonia showing leaves arranged to form compact mosaic. The netted venation of the leaf is very distinctly shown in this plant. (Photo by the Author.)] =774.= Where the leaves of a plant, or a portion of a plant, are approximate and arranged in the form of a pattern, the leaves fitting together to form a more or less even and continuous surface, such patterns are sometimes termed “mosaics,” since the relation of leaves to one another is roughly like the relation of the pieces of a mosaic. A good illustration of a mosaic is presented by a greenhouse plant Fittonia (fig. 441). The stems are prostrate and the erect branches quite short, but it may have quite a wide system by the spreading of the runners; the branches of such a length that the leaves borne near the tips all fit together forming a broad surface of leaves so closely fitted together often that the stems cannot be seen. The advantage of a mosaic over a separate disposition of leaves at somewhat different levels is that the leaves do not shade one another. Were all the light rays coming down at right angles to the leaves, there would not be any shading of the lower ones, but the oblique rays of light would be cut off from many of the leaves. In the case of a mosaic all the rays of light play upon all the leaves. Some of the mosaics which can be observed are as follows: [Illustration: Fig. 442. Rosette pattern of leaves.] =775. Rosette pattern.=—The rosette pattern is presented by many plants with “radial” leaves, or leaves which arise in a cluster near the surface of the ground, and are thus more or less crowded in their arrangement on the stem. The pretty gloxinia often presents fine examples of a loose rosette. In the rosette pattern the petioles of the lower leaves are longer than the upper ones, and the blade is thus carried out beyond the inner leaves. The leaves being so crowded in their attachment to the stem lie very nearly in the same plane.