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.
776. Vines and climbers.—Some of the most extensive mosaic patterns are shown in creeping and climbing vines. A very common example is that of the ivies trained on the walls of buildings, covering in some instances many square yards of surface. Where the vines trail over the ground or clamber over other vegetation, it is interesting to observe the various patterns, and the distortion of petioles brought about by turning of the leaves. Of examples found in greenhouses, the Pellonia is excellent, and the trailing ribbon-grass often forms loose mosaics.
777. Branch patterns.—These patterns are very common. They are often formed in the woods on the ends of branches by the leaves adjusting themselves so as to largely avoid shading each other. [Figure 443] illustrates one of them from a maple branch. It is interesting to note the way in which the leaves fit themselves in the pattern, how in some the petioles have elongated, while others have remained short. Of course, it should be understood that the pattern is made during the growth of the leaves.
Fig. 443.
Spray of leaves of striped maple,
showing different lengths of leafstalks.
Fig. 444.
Cedar of Lebanon, strong light only
from one side of tree (Syria).
778. The tree pattern.—Mosaics are often formed by the exterior foliage on a tree, though they are rarely so regular as some of those mentioned above. Still it is common to see in some trees with drooping limbs like the elm, beautiful and large mosaics. The weeping elm sometimes forms a very close and quite even pattern over the entire outer surface. In most trees the leaf arrangement is not such as to form large patterns, but is more or less open. While the conifers do not form mosaics there are many interesting examples of grouping of foliage on branch systems into broadly expanded areas, as seen in the branches of white pine trees, especially in the edge of a wood, or as seen in the arbor-vitæ.
OTHER PATTERNS.
779. Imbricate pattern of short stems.—This pattern is quite common, and differs from the rosette in that the leaves are distributed further apart on the stem so that the central ones are considerably higher up than in the mosaic. The lower petioles are longer, as in the rosette, so that the outer lower leaves extend further out. Some begonias show fine imbricate patterns.