Fig. 39. A perfect and complete flower. A, petals, all of them forming the corolla; B, sepals, all of them forming the calyx; C, the stamen, composed of (C) the filament, and (C1) the anther, which produces the pollen; D, the pistil, consisting of the swollen base (D) the ovary, a slender shank (D1) the style, and the swollen or branched tip (D2) the stigma. (H. D. House, “Wild Flowers of New York.”) Fig. 40. Typical flower of the pea family. Two petals unite to form the keel (below), two more unite to form the wings (center), the remaining and larger petal forms the standard. In most plants of this family the stamens and pistils are concealed within the keel. Fig. 41. Two-lipped inequilateral flower, common in such plants as Salvia, Snapdragon, etc. Note the united calyx and corolla. Fig. 42. Gamopetalous or united and regular corolla of the Fringed Gentian. Figs. 43, 44, and 45, flowers of the Compositæ or daisy family. Many small flowers grouped in heads and usually surrounded by one or more series of bracts. Fig. 43. Flowers all tubular, the small one at the left being an individual flower. Common examples are Boneset and the common garden Ageratum. Fig. 44. Flowers both tubular and with rays, the tubular in the center and the rays on the margin. Below is an individual tubular flower on the right, and on the left an individual ray flower. Note that its five united divisions correspond to the five petals in other plants. Common examples are the daisy, sunflower, black-eyed Susan, etc. Fig. 45. Flowers all ray flowers, an individual one at the right. The Compositæ with only ray flowers usually have a milky juice and have often been grouped in a separate family, the Cichoriaceæ. Common examples are dandelion, chicory, and lettuce.
surround and often half inclose the brightly colored petals within. This outer covering of flowers is called calyx ([Figure 39] B), the individual parts of it, where they are separated, sepals. Their chief use is to protect the interior petals while they are inclosed in the bud. The calyx may or may not have bracts just underneath it, as it does very conspicuously in the case of the flowering dogwood, whose white “flowers” are really only brightly colored bracts. The transition between bracts and calyx is not difficult to see in many plants, and where it is impossible the evidence from their internal structure confirms what our eye might be inclined to doubt.
Just inside the calyx is what most people call the “flower,” which is really composed of more highly colored sepals, but which we call petals ([Figure 39]A). Where these are joined together the collection, which forms tubular flowers like the lily of the valley, is called a corolla. It is, of course, the petals or corollas of flowering plants that give our landscapes their greatest beauty, their most gorgeous coloring. While this from one point of view amply justifies a prodigal nature in strewing the earth with beautiful flowers, the true value of the color to the plant is in quite other directions, which will be explained a little later.
Toward the base of the corolla, or sometimes on the petals or sepals, may be found a series of slender appendages, usually threadlike or a little thicker, crowned at the top by a distinctly large knob. The individual appendage is known as a stamen ([Figure 39] C), its threadlike portion a filament ([Figure 39] C), and the knoblike top an anther ([Figure 39] C1).
Directly in the middle of the flower there is still another organ, usually swollen at the base, slender in the shank, and either thickened or branched at the tip. This central part of nearly all flowers is called collectively a pistil ([Figure 39] D), its swollen base an ovary ([Figure 39] D), the slender shank the style ([Figure 39] D1), and the thickened or branched tip a stigma ([Figure 39] D2). A perfect and complete flower, then, is composed as follows: