The Elements of Botany Part 9

[Ill.u.s.tration: Fig. 193. 194. 195. 196. 197. 198.]

Section VIII. FLOWERS.

196. Flowers are for the production of seed (16). Stems and branches, which for a time put forth leaves for vegetation, may at length put forth flowers for reproduction.

-- 1. POSITION AND ARRANGEMENT OF FLOWERS, OR INFLORESCENCE.

197. Flower-buds appear just where leaf-buds appear; that is, they are either _terminal_ or _axillary_ (47-49). Morphologically, flowers answer to shoots or branches, and their parts to leaves.

198. In the same species the flowers are usually from axillary buds only, or from terminal buds only; but in some they are both axillary and terminal.

199. =Inflorescence=, which is the name used by Linnaeus to signify mode of flower-arrangement, is accordingly of three cla.s.ses: namely, _Indeterminate_, when the flowers are in the axils of leaves, that is, are from axillary buds; _Determinate_, when they are from terminal buds, and so _terminate_ a stem or branch; and _Mixed_, when these two are combined.

200. =Indeterminate Inflorescence= (likewise, and for the same reason, called _indefinite inflorescence_) is so named because, as the flowers all come from axillary buds, the terminal bud may keep on growing and prolong the stem indefinitely. This is so in Moneywort (Fig. 199).

[Ill.u.s.tration: Fig. 199. Piece of a flowering-stem of Moneywort (Lysimachia nummularia,) with single flowers successively produced in the axils of the leaves, from below upwards, as the stem grows on.]

201. When flowers thus arise singly from the axils of ordinary leaves, they are _axillary_ and _solitary_, not collected into flower-cl.u.s.ters.

202. But when several or many flowers are produced near each other, the accompanying leaves are apt to be of smaller size, or of different shape or character: then they are called BRACTS, and the flowers thus brought together form a cl.u.s.ter. The kinds of flower-cl.u.s.ters of the indeterminate cla.s.s have received distinct names, according to their form and disposition. They are princ.i.p.ally _Raceme_, _Corymb_, _Umbel_, _Spike_, _Head_, _Spadix_, _Catkin_, and _Panicle_.

203. In defining these it will be necessary to use some of the following terms of descriptive botany which relate to inflorescence. If a flower is stalkless, i. e. sits directly in the axil or other support, it is said to be _sessile_. If raised on a naked stalk of its own (as in Fig.

199) it is _pedunculate_, and the stalk is a PEDUNCLE.

204. A peduncle on which a flower-cl.u.s.ter is raised is a _Common peduncle_. That which supports each separate flower of the cl.u.s.ter is a _Partial peduncle_, and is generally called a PEDICEL. The portion of the general stalk along which flowers are disposed is called the _Axis of inflorescence_, or, when covered with sessile flowers, the _Rhachis_ (back-bone), and sometimes the _Receptacle_. The leaves of a flower-cl.u.s.ter generally are termed BRACTS. But when bracts of different orders are to be distinguished, those on the common peduncle or axis, and which have a flower in their axil, keep the name of _bracts_; and those on the pedicels or partial flower-stalks, if any, that of BRACTLETS or _Bracteoles_. The former is the preferable English name.

[Ill.u.s.tration: Fig. 200. A raceme, with a general peduncle (_p_), pedicels (_p'_), bracts (_b_), and bractlets (_b'_). Plainly the bracts here answer to the leaves in Fig. 199.]

205. =A Raceme= (Fig. 200) is that form of flower-cl.u.s.ter in which the flowers, each on their own foot-stalk or pedicel, are arranged along the sides of a common stalk or axis of inflorescence; as in the Lily of the Valley, Currant, Barberry, one section of Cherry, etc. Each flower comes from the axil of a small leaf, or bract, which, however, is often so small that it might escape notice, and even sometimes (as in the Mustard Family) disappears altogether. The lowest blossoms of a raceme are of course the oldest, and therefore open first, and the order of blossoming is _ascending_ from the bottom to the top. The summit, never being stopped by a terminal flower, may go on to grow, and often does so (as in the common Shepherd's Purse), producing lateral flowers one after another for many weeks.

[Ill.u.s.tration: Fig. 201. A raceme. 202. A corymb. 203. An umbel.]

206. =A Corymb= (Fig. 202) is the same as a raceme, except that it is flat and broad, either convex, or level-topped. That is, a raceme becomes a corymb by lengthening the lower pedicels while the uppermost remain shorter. The axis of a corymb is short in proportion to the lower pedicels. By extreme shortening of the axis the corymb may be converted into

207. =An Umbel= (Fig. 203) as in the Milkweed, a sort of flower-cl.u.s.ter where the pedicels all spring apparently from the same point, from the top of the peduncle, so as to resemble, when spreading, the rays of an umbrella; whence the name. Here the pedicels are sometimes called the _Rays_ of the umbel. And the bracts, when brought in this way into a cl.u.s.ter or circle, form what is called an INVOLUCRE.

208. The corymb and the umbel being more or less level-topped, bringing the flowers into a horizontal plane or a convex form, the ascending order of development appears as _Centripetal_. That is, the flowering proceeds from the margin or circ.u.mference regularly towards the centre; the lower flowers of the former answering to the outer ones of the latter.

209. In these three kinds of flower-cl.u.s.ters, the flowers are raised on conspicuous _pedicels_ (204) or stalks of their own. The shortening of these pedicels, so as to render the flowers _sessile_ or nearly so, converts a raceme into a _Spike_, and a corymb or an umbel into a _Head_.

210. =A Spike= is a flower cl.u.s.ter with a more or less lengthened axis, along which the flowers are sessile or nearly so; as in the Plantain (Fig. 204).

[Ill.u.s.tration: Fig. 204. Spike of the common Plantain or Ribwort.]

211. =A Head= (_Capitulum_) is a round or roundish cl.u.s.ter of flowers, which are sessile on a very short axis or receptacle, as in the b.u.t.ton-ball, b.u.t.ton-bush (Fig. 205), and Red Clover. It is just what a spike would become if its axis were shortened; or an umbel, if its pedicels were all shortened until the flowers became sessile. The head of the b.u.t.ton-bush is naked; but that of the Thistle, of the Dandelion, and the like, is surrounded by empty bracts, which form an _Involucre_.

Two particular forms of the spike and the head have received particular names, namely, the _Spadix_ and the _Catkin_.

[Ill.u.s.tration: Fig. 205. Head of the b.u.t.ton-bush (Cephalanthus).]

212. =A Spadix= is a fleshy spike or head, with small and often imperfect flowers, as in the Calla, Indian Turnip, (Fig. 206), Sweet Flag, etc. It is commonly surrounded or embraced by a peculiar enveloping leaf, called a SPATHE.

[Ill.u.s.tration: Fig. 206. Spadix and spathe of the Indian Turnip; the latter cut through below.]

213. =A Catkin, or Ament=, is the name given to the scaly sort of spike of the Birch (Fig. 207) and Alder, the Willow and Poplar, and one sort of flower-cl.u.s.ters of the Oak, Hickory, and the like,--the so-called _Amentaceous_ trees.

[Ill.u.s.tration: Fig. 207. Catkin, or Ament, of Birch.]

214. _Compound_ flower-cl.u.s.ters of these kinds are not uncommon. When the stalks which in the simple umbel are the pedicels of single flowers themselves branch into an umbel, a _Compound Umbel_ is formed. This is the inflorescence of Caraway (Fig. 208), Parsnip, and almost all of the great family of Umbelliferous (umbel-bearing) plants.

[Ill.u.s.tration: Fig. 208. Compound Umbel of Caraway.]

215. The secondary or partial umbels of a compound umbel are UMBELLETS.

When the umbellets are subtended by an involucre, this secondary involucre is called an INVOLUCEL.

216. A _Compound raceme_ is a cl.u.s.ter of racemes racemosely arranged, as in Smilacina racemosa. A _compound corymb_ is a corymb some branches of which branch again in the same way, as in Mountain Ash. A _compound spike_ is a spicately disposed cl.u.s.ter of spikes.

[Ill.u.s.tration: Fig. 209. Diagram of a simple panicle.]

217. =A Panicle=, such as that of Oats and many Gra.s.ses, is a compound flower-cl.u.s.ter of a more or less open sort which branches with apparent irregularity, neither into corymbs nor racemes. Fig. 209 represents the simplest panicle. It is, as it were, a raceme of which some of the pedicels have branched so as to bear a few flowers on pedicels of their own, while others remain simple. A _compound panicle_ is one that branches in this way again and again.

[Ill.u.s.tration: Fig. 210. Diagram of an opposite-leaved plant, with a single terminal flower. 211. Same, with a cyme of three flowers; _a_, the first flower, of the main axis; _b b_, those of branches. 212. Same, with flowers also of the third order, _c c_.]

218. =Determinate Inflorescence= is that in which the flowers are from terminal buds. The simplest case is that of a solitary terminal flower, as in Fig. 210. This stops the growth of the stem; for its terminal bud, becoming a blossom, can no more lengthen in the manner of a leaf-bud.

Any further growth must be from axillary buds developing into branches.

If such branches are leafy shoots, at length terminated by single blossoms, the inflorescence still consists of solitary flowers at the summit of stem and branches. But if the flowering branches bear only bracts in place of ordinary leaves, the result is the kind of flower-cl.u.s.ter called

219. =A Cyme.= This is commonly a flat-topped or convex flower-cl.u.s.ter, like a corymb, only the blossoms are from terminal buds. Fig. 211 ill.u.s.trates the simplest cyme in a plant with opposite leaves, namely, with three flowers. The middle flower, _a_, terminates the stem; the two others, _b b_, terminate branches, one from the axil of each of the uppermost leaves; and being later than the middle one, the flowering proceeds from the centre outwards, or is _Centrifugal_. This is the opposite of the indeterminate mode, or that where all the flower-buds are axillary. If flowering branches appear from the axils below, the lower ones are the later, so that the order of blossoming continues _centrifugal_ or, which is the same thing, _descending_, as in Fig. 213, making a sort of reversed raceme or _false raceme_,--a kind of cl.u.s.ter which is to the true raceme just what the flat cyme is to the corymb.

[Ill.u.s.tration: Fig. 213. Diagram of a simple cyme in which the axis lengthens, so as to take the form of a raceme.]

220. Wherever there are bracts or leaves, buds may be produced from their axils and appear as flowers. Fig. 212 represents the case where the branches, _b b_, of Fig. 211, each with a pair of small leaves or bracts about their middle, have branched again, and produced the branchlets and flowers _c c_, on each side. It is the continued repet.i.tion of this which forms the full or compound cyme, such as that of the Laurestinus, Hobble-bush, Dogwood, and Hydrangea (Fig. 214).

[Ill.u.s.tration: Fig. 214. Compound cyme of Hydrangea arborescens, with neutral enlarged flowers round the circ.u.mference.]

221. =A Fascicle= (meaning a bundle), like that of the Sweet William and Lychnis of the gardens, is only a cyme with the flowers much crowded.

222. =A Glomerule= is a cyme still more compacted, so as to imitate a head. It may be known from a true head by the flowers not expanding centripetally, that is, not from the circ.u.mference towards the centre.

223. The ill.u.s.trations of determinate or _cymose_ inflorescence have been taken from plants with opposite leaves, which give rise to the most regular cymes. But the Rose, Cinquefoil, b.u.t.tercup, etc., with alternate leaves, furnish also good examples of cymose inflorescence.

224. =A Cymule= (or diminutive cyme) is either a reduced small cyme of few flowers, or a branch of a compound cyme, i. e. a partial cyme.

225. =Scorpioid= or =Helicoid Cymes=, of various sorts, are forms of determinate inflorescence (often puzzling to the student) in which one half of the ramification fails to appear. So that they may be called _incomplete cymes_. The commoner forms may be understood by comparing a complete cyme, like that of Fig. 215 with Fig. 216, the diagram of a cyme of an opposite-leaved plant, having a series of terminal flowers and the axis continued by the development of a branch in the axil of only one of the leaves at each node. The dotted lines on the left indicate the place of the wanting branches, which if present would convert this _scorpioid cyme_ into the complete one of Fig. 215. Fig.