Fig. 772.—Pentamerous corolla.
Fig. 773.—Monopetalous corolla.
The petals differ from ordinary leaves, and in them we find all the beautiful tints and the odour we imbibe from blossoms. The forms of corolla correspond to those of the calyx, and are called by the same names. But when corollas are absent the petals of course cannot provide the necessary colours for the flower. Then the calyx is gifted, and the sepals are brilliant. Thus Nature provides for everything.
Corollas are found with five or ten petals, and sometimes with three, six, and nine—the numbers always doubling or adding the original number. There may be four petals or eight, as in the “tetramerous” corolla (fig. 771). Instances of others are illustrated, and a plant whose petals, sepals, and stamens are numerically equal, or are multiples of each other, are termed “symmetrical.” The “regular” flower does not vary much, as the petals are of the same size and shape, but there are many “irregular” flowers—as the pea—in which portions of the calyx or corolla are of different shapes. The “labiate” and the “campanulate” are illustrated in figs. 774, 775, including the convolvulus and the snap-dragon. These are but a few examples of an almost endless diversity. The “regular” flowers—exemplified in the buttercup and convolvulus—always present the same figure to the observer.
Fig. 774.—Labiate corolla.
Fig. 775.—Campanulate.