The Elements of Botany Part 10

217 is a diagram of similar inflorescence with alternate leaves. Both are kinds of _false racemes_ (219). When the bracts are also wanting in such cases, as in many Borragineous plants, the true nature of the inflorescence is very much disguised.

[Ill.u.s.tration: Fig. 215. A complete forking cyme of an Arenaria, or Chickweed.]

[Ill.u.s.tration: Fig. 216. Diagram of a scorpioid cyme, with opposite leaves or bracts.]

[Ill.u.s.tration: Fig. 217. Diagram of a.n.a.logous scorpioid cyme, with alternate leaves or bracts.]

226. These distinctions between determinate and indeterminate inflorescence, between corymbs and cymes, and between the true and the false raceme and spike, were not recognized by botanists much more than half a century ago, and even now are not always attended to in descriptions. It is still usual and convenient to describe rounded or flat-topped and open ramification as _corymbose_, even when essentially cymose; also to call the reversed or false racemes or spikes by these (strictly incorrect) names.

227. =Mixed Inflorescence= is that in which the two plans are mixed or combined in compound cl.u.s.ters. A _mixed panicle_ is one in which, while the primary ramification is of the indeterminate order, the secondary or ultimate is wholly or partly of the determinate order. A contracted or elongated inflorescence of this sort is called a THYRSUS. Lilac and Horse-chestnut afford common examples of mixed inflorescence of this sort. When loose and open such flower-cl.u.s.ters are called by the general name of _Panicles_. The heads of Compositae are centripetal; but the branches or peduncles which bear the heads are usually of centrifugal order.

-- 2. PARTS OR ORGANS OF THE FLOWER.

228. These were simply indicated in Section II. 16. Some parts are necessary to seed-bearing; these are _Essential Organs_, namely, the _Stamens_ and _Pistils_. Others serve for protection or for attraction, often for both. Such are the leaves of the Flower, or the _Floral Envelopes_.

229. =The Floral Envelopes=, taken together, are sometimes called the PERIANTH, also _Perigone_, in Latin form _Perigonium_. In a flower which possesses its full number of organs, the floral envelopes are of two kinds, namely, an outer circle, the CALYX, and an inner, the COROLLA.

230. =The Calyx= is commonly a circle of green or greenish leaves, but not always. It may be the most brightly colored part of the blossom.

Each calyx-leaf or piece is called a SEPAL.

231. =The Corolla= is the inner circle of floral envelopes or flower-leaves, usually of delicate texture and _colored_, that is, of some other color than green. Each corolla-leaf is called a PETAL.

232. There are flowers in abundance which consist wholly of floral envelopes. Such are the so-called full _double flowers_, of which the choicer roses and camellias of the cultivator are familiar examples. In them, under the gardener's care and selection, petals have taken the place of both stamens and pistils. These are monstrous or unnatural flowers, incapable of producing seed, and subservient only to human gratification. Their common name of _double_ flowers is not a sensible one: except that it is fixed by custom, it were better to translate their Latin name, _flores pleni_, and call them _full flowers_, meaning full of leaves.

233. Moreover, certain plants regularly produce _neutral flowers_, consisting of floral envelopes only. In Fig. 214, some are seen around the margin of the cyme in Hydrangea. They are likewise familiar in the Hobble-bush and in Wild-Cranberry tree, Viburnum Oxycoccus; where they form an attractive setting to the cl.u.s.ter of small and comparatively inconspicuous perfect flowers which they adorn. In the Guelder Rose, or Snow-ball of ornamental cultivation, all or most of the blossoms of this same shrub are transformed into neutral flowers.

[Ill.u.s.tration: Fig. 218. A _flos plenus_, namely, a full double flower of Rose.]

234. =The Essential Organs= are likewise of two kinds, placed one above or within the other; namely, first, the STAMENS or fertilizing organs, and second, the PISTILS, which are to be fertilized and bear the seeds.

[Ill.u.s.tration: Fig. 219. A stamen: _a_, filament; _b_, anther, discharging pollen.]

[Ill.u.s.tration: Fig. 220. A pistil; with ovary, _a_, half cut away, to show the contained ovules; _b_, style; _c_, stigma.]

235. =A Stamen= consists of two parts, namely, the FILAMENT or stalk (Fig. 219 _a_), and the ANTHER (_b_). The latter is the only essential part. It is a case, commonly with two lobes or cells, each opening lengthwise by a slit, at the proper time, and discharging a powder or dust-like substance, usually of a yellow color. This powder is the POLLEN, or fertilizing matter, to produce which is the office of the stamen.

236. =A Pistil= (Fig. 220, 221) when complete, has three parts; OVARY, STYLE, and STIGMA. The _Ovary_, at base, is the hollow portion, which contains one or more OVULES or rudimentary seeds. The _Style_ is the tapering portion above: the _Stigma_ is a portion of the style, usually its tip, with moist naked surface, upon which grains of pollen may lodge and adhere, and thence make a growth which extends down to the ovules.

When there is no style then the stigma occupies the tip of the ovary.

[Ill.u.s.tration: Fig. 221. Model of a simple pistil, with ovary cut across and slightly opened ventrally, to show the ovules and their attachment.]

237. =The Torus= or =Receptacle= is the end of the flower-stalk, or the portion of axis or stem out of which the several organs of the flower grow, upon which they are borne (Fig. 223).

[Ill.u.s.tration: Fig. 222. Flower of Sedum ternatum, a Stonecrop.]

[Ill.u.s.tration: Fig. 223. Parts of same, two of each kind, separated and displayed; the torus or receptacle in the centre; _a_, a sepal; _b_, a petal; _c_, a stamen; _d_, a pistil.]

238. The parts of the flower are thus disposed on the receptacle or axis essentially as are leaves upon a very short stem; first the sepals, or outer floral leaves; then the petals or inner floral leaves; then the stamens; lastly, at summit or centre, the pistils, when there are two or more of them, or the single pistil, when only one. Fig. 223 shows the organs displayed, two of each kind, of such a simple and symmetrical flower as that of a Sedum or Stonecrop, Fig. 222.

-- 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. Cra.s.sula, 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.

[Ill.u.s.tration: Fig. 224. Flower of a Cra.s.sula. 225. Diagram or ground-plan of same.]

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 ill.u.s.tration 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 cla.s.s 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.

[Ill.u.s.tration: Fig. 226. Flower of a Trillium; its parts in threes.]

[Ill.u.s.tration: Fig. 227. Diagram of flower of Trillium. In this, as in all such diagrams of cross-section of blossoms, the parts of the outer circle represent the calyx; the next, corolla; within, stamens (here in two circles of three each, and the cross-section is through the anthers); in the centre, section of three ovaries joined into a compound one of three cells.]

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 circ.u.mstances 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.

[Ill.u.s.tration: Fig. 228. Series of sepals, petals, and stamens of White Water-Lily, showing the transitions.]

[Ill.u.s.tration: Fig. 229. A Cactus blossom.]

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 cl.u.s.ter 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.

-- 4. MODIFICATIONS OF THE TYPE.

248. =The Deviations=, as they may be called, from the a.s.sumed type or pattern of flower are most various and extensive. The differences between one species and another of the same genus are comparatively insignificant; those between different genera are more striking; those between different families and cla.s.ses of plants more and more profound.

They represent different adaptations to conditions or modes of life, some of which have obvious or probable utilities, although others are beyond particular explanation. The princ.i.p.al modifications may be conveniently cla.s.sified. First those which in place of perfect (otherwise called _hermaphrodite_ or bis.e.xual) flowers, give origin to

249. =Unis.e.xual, or Separated, or Diclinous Flowers=, _imperfect_ flowers, as they have been called in contradistinction to perfect flowers; but that term is too ambiguous. In these some flowers want the stamens, while others want the pistils. Taking hermaphrodite flowers as the pattern, it is natural to say that the missing organs are _suppressed_. This expression is justified by the very numerous cases in which the missing parts are _abortive_, that is, are represented by rudiments or vestiges, which serve to exemplify the plan, although useless as to office. Unis.e.xual flowers are