§ 3 Plan of Flower
239. All flowers are formed upon one general plan, but with almost infinite variations, and many disguises. This common plan is best understood by taking for a type, or standard for comparison, some perfect, complete, regular, and symmetrical blossom, and one as simple as such a blossom could well be. Flowers are said to be
Perfect (hermaphrodite), when provided with both kinds of essential organs, i. e. with both stamens and pistils.
Complete, when, besides, they have the two sets of floral envelopes, namely, calyx and corolla. Such are completely furnished with all that belongs to a flower.
Regular, when all the parts of each set are alike in shape and size.
Symmetrical, when there is an equal number of parts in each set or circle of organs.
240. Flax-flowers were taken for a pattern in Section II. 16. But in them the five pistils have their ovaries as it were consolidated into one body. Sedum, Fig. 222, has the pistils and all the other parts free from such combination. The flower is perfect, complete, regular, and symmetrical, but is not quite as simple as it might be; for there are twice as many stamens as there are of the other organs. Crassula, a relative of Sedum, cultivated in the conservatories for winter blossoming (Fig. 224) is simpler, being isostemonous, or with just as many stamens as petals or sepals, while Sedum is diplostemonous, having double that number: it has, indeed, two sets of stamens.
241. Numerical Plan. A certain number either runs through the flower or is discernible in some of its parts. This number is most commonly either five or three, not very rarely four, occasionally two. Thus the ground-plan of the flowers thus far used for illustration is five. That of Trillium (Fig. 226, 227) is three, as it likewise is as really, if not as plainly, in Tulips and Lilies, Crocus, Iris, and all that class of blossoms. In some Sedums all the flowers are in fours. In others the first flowers are on the plan of five, the rest mostly on the plan of four, that is, with four sepals, four petals, eight stamens (i. e. twice four), and four pistils. Whatever the ground number may be, it runs through the whole in symmetrical blossoms.
242. Alternation of the successive Circles. In these flowers the parts of the successive circles alternate; and such is the rule. That is, the petals stand over the intervals between the sepals; the stamens, when of the same number, stand over the intervals between the petals; or when twice as many, as in the Trillium, the outer set alternates with the petals, and the inner set, alternating with the other, of course stands before the petals; and the pistils alternate with these. This is just as it should be on the theory that the circles of the blossom answer to whorls of leaves, which alternate in this way. While in such flowers the circles are to be regarded as whorls, in others they are rather to be regarded as condensed spirals of alternate leaves. But, however this may be, in the mind of a morphological botanist,
243. Flowers are altered Branches, and their parts, therefore, altered leaves. That is, certain buds, which might have grown and lengthened into a leafy branch, do, under other circumstances and to accomplish other purposes, develop into blossoms. In these the axis remains short, nearly as it is in the bud; the leaves therefore remain close together in sets or circles; the outer ones, those of the calyx, generally partake more or less of the character of foliage; the next set are more delicate, and form the corolla, while the rest, the stamens and pistils, appear under forms very different from those of ordinary leaves, and are concerned in the production of seed. This view gives to Botany an interest which one who merely notices the shape and counts the parts of blossoms, without understanding their plan, has no conception of.
244. That flowers answer to branches may be shown, first, from their position. As explained in the section on Inflorescence, flowers arise from the same places as branches, and from no other; flower-buds, like leaf-buds, appear either on the summit of a stem, that is, as a terminal bud, or in the axil of a leaf, as an axillary bud. And, as the plan of a symmetrical flower shows, the arrangement of the parts on their axis or receptacle is that of leaves upon the stem.
245. That the sepals and petals are of the nature of leaves is evident from their appearance; they are commonly called the leaves of the flower. The calyx is most generally green in color, and foliaceous (leaf-like) in texture. And though the corolla is rarely green, yet neither are proper leaves always green. In our wild Painted-cup, and in some scarlet Sages, common in gardens, the leaves just under the flowers are of the brightest red or scarlet, often much brighter-colored than the corolla itself. And sometimes (as in many Cactuses, and in Carolina Allspice) there is such a regular gradation from the last leaves of the plant (bracts or bractlets) into the leaves of the calyx, that it is impossible to say where the one ends and the other begins. If sepals are leaves, so also are petals; for there is no clearly fixed limit between them. Not only in the Carolina Allspice and Cactus (Fig. 229), but in the Water-Lily (Fig. 228) and in a variety of flowers with more than one row of petals, there is such a complete transition between calyx and corolla that no one can surely tell how many of the leaves belong to the one and how many to the other.
246. That stamens are of the same general nature as petals, and therefore a modification of leaves, is shown by the gradual transitions that occur between the one and the other in many blossoms; especially in cultivated flowers, such as Roses and Camellias, when they begin to double, that is, to change their stamens into petals. Some wild and natural flowers show the same interesting transitions. The Carolina Allspice and the White Water-Lily exhibit complete gradations not only between sepals and petals, but between petals and stamens. The sepals of our Water-Lily are green outside, but white and petal-like on the inside; the petals, in many rows, gradually grow narrower towards the centre of the flower; some of these are tipped with a trace of a yellow anther, but still are petals; the next are more contracted and stamen-like, but with a flat petal-like filament; and a further narrowing of this completes the genuine stamen.
247. Pistils and stamens now and then change into each other in some Willows; pistils often turn into petals in cultivated flowers; and in the Double Cherry they are occasionally replaced by small green leaves. Sometimes a whole blossom changes into a cluster of green leaves, as in the “green roses” occasionally noticed in gardens, and sometimes it degenerates into a leafy branch. So the botanist regards pistils also as answering to leaves; that is, to single leaves when simple and separate, to a whorl of leaves when conjoined.