The labiate corolla is characteristic of the mint family where the gamosepalous corolla is unequally divided, so that the two upper lobes are sharply separated from the three lower forming two “lips.” The labiate corolla of the toad-flax, or snapdragon is personate, or masked, because the lower lip arches upward like a palate and closes the entrance to the corolla tube; that of the dead nettle (Lamium) is ringent or gaping, because the lips are spread wide apart. In some plants the labiate corolla is not very marked and differs but slightly from a regular form.
The ligulate or strap-shaped corolla is characteristic of the flowers of the dandelion or chicory, or of the ray flowers of other composites ([fig. 451]). The lower part of the gamosepalous corolla is tubular, and the upper part is strap-shaped, as if that part of the tube were split on one side and spread out flat.
These forms of the flower should be studied in appropriate examples.
813. Union of flower parts.—In the buttercup flower all the parts of each series are separate from one another and from other series of parts. Each one is attached to the receptacle of the flower, which is a very much shortened portion of the flower axis. The calyx being composed of separate and distinct parts is said to be polysepalous, and the corolla is likewise polypetalous. The stamens are distinct, and the pistils are simple. In many flowers, however, there is a greater or lesser union of parts.
814. Union of parts of the same series or cycle.—The parts coalesce, either slightly or to a great extent. Usually they are not so completely coalesced but what the number of parts of the series can be determined. Where the sepals are united the calyx is gamosepalous, when the petals are united the corolla is gamopetalous.
Union of the sepals or of the corolla is quite common, but union of the stamens is rare except in a few families where it is quite characteristic. When the stamens are united by their anthers, they are syngenœsious. This is the case in most flowers of the composite family. When all the stamens are united into one group by their filaments, they are monadelphous (one brotherhood), as in hollyhock, hibiscus, cotton, marsh-mallow, etc. When they are united by their filaments in two groups, they are diadelphous (two brotherhoods), as in the pea and most members of the pea family. In most species of St. John’s wort (Hypericum), the stamens are united in threes (triadelphous).
815. The carpels are often united.—The pistil is then said to be compound. Where the pistils are consolidated, usually the adjacent walls coalesce and thus separate the cavity of each ovary. Each cavity in the compound pistil is a locule. In some cases the adjacent walls disappear so that there is one common cavity for the compound pistil (examples: purslane, chickweeds, pinks, etc.). In a few cases there is a false partition (example, in the toothwort and other crucifers). The compound pistil is very often lobed slightly, so that the different pistils can be discerned. More often the styles or stigmas are distinct, and thus indicate the number of pistils united.
816. Union of the parts of different series.—While in the buttercup and many other flowers, all the different parts are inserted on the torus or receptacle, in other flowers one series of parts may be joined to another. This is adnation of parts, or the two or more series are adnate. In the morning glory the stamens are inserted on the inner face of the corolla tube; the same is true in the mint family, and there are many other examples. The insertion of parts, whether free or adnate, is usually spoken of in reference to their relation to the pistil. Thus, in the buttercup the floral envelopes and stamens are all free and hypogynous, they are below the pistil. The pistil in this case is superior. In the cherry, pear, etc., the petals and stamens are borne on the edge of the more or less elevated tube of the calyx, and are said to be perigynous, i.e., around the pistil. In the cranberry, huckleberry, etc., the calyx is for the most part united with the wall of the ovary with the short calyx limbs projecting from the upper surface. The petals and stamens are inserted on the edge of the calyx above the ovary; they are, therefore, epigynous, and the ovary being under the calyx, as it were, is inferior.
[III. Arrangement of Flowers, or Mode of Inflorescence.]
817. Flowers are solitary or clustered.—Solitary flowers are more simple in their arrangement, i.e., it is easier for us to determine and name their relation to each other and to other parts of the plant. They are either axillary, i.e., on short lateral shoots in the axils of ordinary foliage leaves, or they are terminal, i.e., they are borne on the end of the main axis of an ordinary foliage shoot. In either case they are so far separated, and the foliage leaves are so prominent, they do not form recognizable groups or clusters. The manner of arrangement of flowers on the shoot is called inflorescence, while the group of flowers so arranged is the flower cluster.