Part 7

184. No two or more leaves ever grow from the same point. The so-called _Fascicled_ or _Clustered_ leaves are the leaves of a branch the nodes of which are very close, just as they are in the bud, so keeping the leaves in a cluster. This is evident in the Larch (Fig. 184), in which examination shows each cluster to be made up of numerous leaves crowded on a spur or short axis. In spring there are only such clusters; but in summer some of them lengthen into ordinary shoots with scattered alternate leaves. So, likewise, each cluster of two or three needle-shaped leaves in Pitch Pines (as in Fig. 185), or of five leaves in White Pine, answers to a similar extremely short branch, springing from the axil of a thin and slender scale, which represents a leaf of the main shoot. For Pines produce two kinds of leaves,--1. primary, the proper leaves of the shoots, not as foliage, but in the shape of delicate scales in spring, which soon fall away; and 2. secondary, the _fascicled_ leaves, from buds in the axils of the former, and these form the actual foliage.

185. =Phyllotaxy of Alternate Leaves.= Alternate leaves are distributed along the stem in an order which is uniform for each species. The arrangement in all its modifications is said to be _spiral_, because, if we draw a line from the _insertion_ (i. e. the point of attachment) of one leaf to that of the next, and so on, this line will wind spirally around the stem as it rises, and in the same species will always bear the same number of leaves for each turn round the stem. That is, any two successive leaves will always be separated from each other by an equal portion of the circumference of the stem. The distance in _height_ between any two leaves may vary greatly, even on the same shoot, for that depends upon the length of the _internodes_, or spaces between the leaves; but the distance as measured around the circumference (in other words, the _Angular Divergence_, or angle formed by any two successive leaves) is uniformly the same.

186. =Two-ranked.= The greatest possible divergence is, of course, where the second leaf stands on exactly the opposite side of the stem from the first, the third on the side opposite the second, and therefore over the first, and the fourth over the second. This brings all the leaves into two ranks, one on one side of the stem and one on the other, and is therefore called the _Two-ranked_ arrangement. It occurs in all Grasses,--in Indian Corn, for instance; also, in the Basswood (Fig. 181). This is the simplest of all arrangements, and the one which most widely distributes successive leaves, but which therefore gives the fewest vertical ranks. Next is the

187. =Three-ranked= arrangement,--that of all Sedges, and of White Hellebore. Here the second leaf is placed one third of the way round the stem, the third leaf two thirds of the way round, the fourth leaf accordingly directly over the first, the fifth over the second, and so on. That is, three leaves occur in each turn round the stem, and they are separated from each other by one third of the circumference. (Fig. 186, 187.)

188. =Five-ranked= is the next in the series, and the most common. It is seen in the Apple (Fig. 188), Cherry, Poplar, and the greater number of trees and shrubs. In this case the line traced from leaf to leaf will pass twice round the stem before it reaches a leaf situated directly over any below (Fig. 189). Here the sixth leaf is over the first; the leaves stand in five perpendicular ranks, with equal angular distance from each other; and this distance between any two successive leaves is just two fifths of the circumference of the stem.

189. The five-ranked arrangement is expressed by the fraction 2/5. This fraction denotes the divergence of the successive leaves, i. e. the angle they form with each other: the numerator also expresses the number of turns made round the stem by the spiral line in completing one cycle or set of leaves, namely, two; and the denominator gives the number of leaves in each cycle, or the number of perpendicular ranks, namely, five. In the same way the fraction 1/2 stands for the two-ranked mode, and 1/3 for the three-ranked: and so these different sorts are expressed by the series of fractions 1/2, 1/3, 2/5. Other cases follow in the same numerical progression, the next being the

190. =Eight-ranked= arrangement. In this the ninth leaf stands over the first, and three turns are made around the stem to reach it; so it is expressed by the fraction 3/8. This is seen in the Holly, and in the common Plantain. Then comes the

191. =Thirteen-ranked= arrangement, in which the fourteenth leaf is over the first, after five turns around the stem. The common Houseleek (Fig. 191) is a good example.

192. The series so far, then, is 1/2, 1/3, 2/5, 3/8, 5/13; the numerator and the denominator of each fraction being those of the two next preceding ones added together. At this rate the next higher should be 8/21, then 13/34, and so on; and in fact just such cases are met with, and (commonly) no others. These higher sorts are found in the Pine Family, both in the leaves and the cones and in many other plants with small and crowded leaves. But in those the number of the ranks, or of leaves in each cycle, can only rarely be made out by direct inspection. They may be indirectly ascertained, however, by studying the _secondary_ spirals, as they are called, which usually become conspicuous, at least two series of them, one turning to the right and one to the left, as shown in Fig. 191. For an account of the way in which the character of the phyllotaxy may be deduced from the secondary spirals, see Structural Botany, Chapter IV.

193. =Phyllotaxy of Opposite and whorled Leaves.= This is simple and comparatively uniform. The leaves of each pair or whorl are placed over the intervals between those of the preceding, and therefore under the intervals of the pair or whorl next above. The whorls or pairs alternate or cross each other, usually at right angles, that is, they _decussate_. Opposite leaves, that is, whorls of two leaves only, are far commoner than whorls of three or four or more members. This arrangement in successive decussating pairs gives an advantageous distribution on the stem in four vertical ranks. Whorls of three give six vertical ranks, and so on. Note that in descriptive botany leaves in whorls of two are simply called _opposite_ leaves; and that the term _verticillate_ or _whorled_, is employed only for cases of more than two, unless the latter number is specified.

194. =Vernation or Praefoliation=, the disposition of the leaf-blades in the bud, comprises two things; 1st, the way in which each separate leaf is folded, coiled, or packed up in the bud; and 2d, the arrangement of the leaves in the bud with respect to one another. The latter of course depends very much upon the phyllotaxy, i. e. the position and order of the leaves upon the stem. The same terms are used for it as for the arrangement of the leaves of the flower in the flower-bud. See, therefore, "AEstivation, or Praefloration."

195. As to each leaf separately, it is sometimes _straight_ and open in vernation, but more commonly it is either _bent_, _folded_, or _rolled up_. When the upper part is bent down upon the lower, as the young blade in the Tulip-tree is bent upon the leaf-stalk, it is said to be _Inflexed_ or _Reclined_ in vernation. When folded by the midrib so that the two halves are placed face to face, it is _Conduplicate_ (Fig. 193), as in the Magnolia, the Cherry, and the Oak. When folded back and forth like the plaits of a fan, it is _Plicate_ or _Plaited_ (Fig. 194), as in the Maple and Currant. If rolled, it may be so either from the tip downwards, as in Ferns and the Sundew (Fig. 197), when in unrolling it resembles the head of a crosier, and is said to be _Circinate_; or it may be rolled up parallel with the axis, either from one edge into a coil, when it is _Convolute_ (Fig. 195), as in the Apricot and Plum; or rolled from both edges towards the midrib,--sometimes inwards, when it is _Involute_ (Fig. 198), as in the Violet and Water-Lily; sometimes outwards, when it is _Revolute_ (Fig. 196), in the Rosemary and Azalea. The figures are diagrams, representing sections through the leaf, in the way they were represented by Linnaeus.

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.

Sec. 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 classes: 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).

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

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 cluster. The kinds of flower-clusters of the indeterminate class have received distinct names, according to their form and disposition. They are principally _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-cluster is raised is a _Common peduncle_. That which supports each separate flower of the cluster 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-cluster 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.

205. =A Raceme= (Fig. 200) is that form of flower-cluster 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.

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-cluster 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 cluster 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 circumference 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-clusters, 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 cluster with a more or less lengthened axis, along which the flowers are sessile or nearly so; as in the Plantain (Fig. 204).

211. =A Head= (_Capitulum_) is a round or roundish cluster of flowers, which are sessile on a very short axis or receptacle, as in the Button-ball, Button-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 Button-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_.

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.

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-clusters of the Oak, Hickory, and the like,--the so-called _Amentaceous_ trees.

214. _Compound_ flower-clusters 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.

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 cluster 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 cluster of spikes.

217. =A Panicle=, such as that of Oats and many Grasses, is a compound flower-cluster 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.

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-cluster called

219. =A Cyme.= This is commonly a flat-topped or convex flower-cluster, like a corymb, only the blossoms are from terminal buds. Fig. 211 illustrates 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 cluster which is to the true raceme just what the flat cyme is to the corymb.

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 repetition of this which forms the full or compound cyme, such as that of the Laurestinus, Hobble-bush, Dogwood, and Hydrangea (Fig. 214).

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 circumference towards the centre.

223. The illustrations 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, Buttercup, 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. 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.

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 clusters. 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-clusters 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.

Sec. 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_.