An introduction to physiological and systematical botany/Chapter 18
OF THE INFLORESCENCE, OR MODE OF FLOWERING, AND ITS VARIOUS FORMS.
Inflorescence, inflorescentia, is used by Linnæus to express the particular manner in which flowers are situated upon a plant, denominated by preceding writers the modus florendi, or manner of flowering. Of this the several kinds are distinguished as follows.
Verticillus. A Whorl. In this the flowers surround the stem in a sort of ring; though they may not perhaps be inserted on all sides of it, but merely on two opposite ones, as in Dead Nettle, Lamium, Engl. Bot. t. 768—770, Mentha rubra, t. 1413, and Clinopodium vulgare, t. 1401; or even on one side only, as Rumex maritimus, t. 725. The flowers of Hippuris vulgaris, t. 763, are truly inserted in a ring round the stem; but they are not whorled independent of the leaves, and are therefore more properly, with a reference to the leaves, denominated axillary and solitary.
Racemus, a Cluster, or Raceme, consists of numerous rather distant flowers, each on its own proper stalk, and all connected by one common stalk, as a bunch of Currants, Ribes rubrum, Engl. Bot. t. 1289, nigrum, t. 1291, and Orobus sylvaticus, t. 518. A cluster is most generally drooping or pendulous, and the flowers are all expanded nearly at the same time.
A compound racemus occurs in Solanum Dulcamara, t. 565, and an aggregate one, several being gathered together, in Actæa racemosa, Dill. Elth. t. 67; but the example of a bunch of Grapes, quoted by Linnæus for a racemus, appears to me a true thyrsus; see below.
Spica, a Spike, bears numerous flowers ranged along one common stalk, without any partial stalks, as in Satyrium hircinum, Engl. Bot. t. 34, Orchis bifolia, t. 22, Plantago major, t. 1558, and media, t. 1559, Potamogeton heterophyllum, t. 1285, and fluitans, t. 1286; but this is so seldom the case, that a little latitude is allowed. Veronica spicata, t. 2, therefore, and Ribes spicatum, t. 1290, as well as the Common Lavender, Lavandula Spica, are sufficiently good examples of a spike, though none of them has entirely sessile flowers; and Linnæus uses the term in numerous instances where it is still less correctly applicable. A spike generally grows erect. Its mode of expansion is much more progressive than that of the raceme, so that a long period elapses between the fading of the lowest flowers and the opening of the upper ones. The flowers are commonly all crowded close together, or if otherwise, they form separate groups, perhaps whorls, when the spike is said to be either interrupted, or whorled; as in some Mints. In Sanguisorba officinalis the spike begins flowering at the top. See Capitulum below.
Spica secunda, a spike whose flowers lean all to one side, occurs in Nardus stricta, Engl. Bot. t. 290.
Spicula, a Spikelet, is applied exclusively to grasses that have many florets in one calyx, such florets, ranged on a little stalk, constituting the spikelet, which is therefore a part of the flower itself, and not of the inflorescence; see Poa aquatica, t. 1315, fluitans, t. 1520, Briza minor, t. 1316, &c.
Corymbus, a Corymb, is a spike whose partial flower-stalks are gradually longer as they stand lower on the common stalk, so that all the flowers are nearly on a level, of which Spiræa opulifolia, a common shrub in gardens, is an excellent specimen. The Linnæan class Tetradynamia exemplifies this less perfectly, as Cardamine pratensis, Engl. Bot. t. 776, Cheiranthus sinuatus, t. 462, and the common Cabbage, Brassica oleracea, t. 637, in which the corymbus of flowers becomes a racemus of fruit, as happens also in that section of the Veronicæ, entitled by Linnæus corymboso-racemosæ. The flowers of Yarrow, Achillea, t. 757 and 758, and several others of the compound class, as well as the Mountain Ash, t. 337 grow in a corymbose manner, though their inflorescence may not come exactly under the above definition. It is worthy of remark that Linnæus in that definition uses the word spica, not racemus, nor has he corrected it in his own copy of Phil. Bot. p. 41, though he has properly altered a slip of the pen in the same line, petiolis, to pedunculis. This shows he did not restrain his idea of a spike absolutely to sessile flowers, but admitted that extended signification which nature justifies. Many plants acquire partial stalks as the fruit advances towards maturity.
Fasciculus, a Fascicle, is applied to flowers on little stalks, variously inserted and subdivided, collected into a close bundle, level at the top, as the Sweet William, Dianthus barbatus, Curt. Mag. t. 207, and D. Armeria, Engl. Bot. t. 317.t. 1312, might be esteemed a capitulum, because its upper flowers come first to perfection, as in Adoxa, which seems contrary to the nature of a spike; but it does not appear that all capitate flowers expand in the same way, and Sanguisorba canadensis has a real spike, flowering in the usual manner, from the bottom upwards. So Allium descendens, Curt. Mag. 251, opens its upper, or central, flowers first, contrary to the usual order in its genus; both which instances prove such a diversity to be of small moment.
Umbella, an Umbel, for which some authors retain the obsolete old English name of Rundle. In this several flower-stalks, or rays, nearly equal in length, spread from one common centre, their summits forming a level, convex, or even globose surface, more rarely a concave one. When each ray is simple and single-flowered, it is called a simple umbel, as those of Allium ursinum, Engl. Bot. t. 122, Ivy, t. 1267, Primula veris, t. 5, farinosa, t. 6, elatior, t. 513, and Eucalyptus resinifer, Exot. Bot. t. 84. In a compound umbel each ray or stalk mostly bears an umbellula, or partial umbel, as Athamanta Libanotis, Engl. Bot. t. 138. This is usually the case in the very natural order of plants called umbelliferous, to which the last-mentioned, as well as the common Carrot, Parsnep, Parsley, Hemlock, &c. belongs.
A few only of this order have simple umbels, as Hydrocotyle vulgaris, t. 751, and the curious Astrantiæ and Eriocaliæ, Exot. Bot. t. 76—79. In Euphorbia the umbel is differently compounded, consisting of 3, 4, 5 or numerous rays, each of which is repeatedly subdivided, either in a threefold or forked manner. See Engl. Bot. t. 883, 959. &c.
Cyma, a Cyme, has the general appearance of an umbel, and agrees with it so far that its common stalks all spring from one centre, but differs in having those stalks variously and alternately subdivided. Examples are found in Viburnum, Engl. Bot. t. 331, 332, and the common Laurustinus, as also in Sambucus, Elder, t. 475, 476. This mode of inflorescence agrees with a corymbus also in general aspect, but in the latter the primary stalks have no common centre, though the partial ones may sometimes be umbellate, which last case is precisely the reverse of a cyma.
Panicula, a Panicle, bears the flowers in a sort of loose subdivided bunch or cluster, without any order. When the stalks are distant, it is called diffuse, a lax or spreading panicle, as in Saxifraga umbrosa, t. 663, so frequent in gardens under the name of London Pride, and S. Geum, t. 1561, but particularly in many grasses, as the common cultivated Oat, and Avena strigosa, t. 1266; in this tribe the branches of the panicle are mostly semi-verticillate; see Aira aquatica, t. 1557. A divaricated panicle is still more spreading, like those of Prenanthes muralis, t. 457, and Spergula arvensis, t. 1535; the last being dichotomous or forked. A dense or crowded panicle, coarctata, is observable in Milium lendigerum, t. 1107, and Agrostis stolonifera, t. 1532, but still more remarkably in Phleum paniculatum, t. 1077, whose inflorescence looks, at first sight, like a cylindrical spike, but when bent to either side, it separates into branched lobes, constituting a real panicle.
Thyrsus, a Bunch, is a dense or close panicle, more or less of an ovate figure, of which the Lilac, Syringa vulgaris, Curt. Mag. t. 183, Tussilago hybrida and Petasites, Engl. Bot. t. 430, 431, are examples cited by Linnæus. I presume likewise to consider a bunch of grapes, Vitis vinifera, as a true thyrsus, to the characters and appearance of which it correctly answers. Its ultimate terminations are sometimes obscurely umbellate, especially while in blossom, which is no objection here, but can never be the case in a racemus, whether simple or compound. See Racemus.
Of simple flower-stalks, whether solitary or clustered, radical or cauline, axillary, lateral or terminal, we have already spoken.
Linnæus remarks that the most elegant specific characters are taken from the inflorescence. Thus the Apple, Engl. Bot. t. 179, and the Pear, form two species of Pyrus, so far at least a most natural genus, the former of which bears an umbel, the latter a corymb. Pyrola uniflora, t. 146, secunda, t. 517, and umbellata, Curt. Mag., t. 778, are admirably distinguished by their several forms of inflorescence.
- It might be expected from the numerous learned editors and copiers of this and other works of Linnæus, that they should correct such manifest errors as the above which any tyro might perceive.