An introduction to physiological and systematical botany/Chapter 15
OF LEAVES, THEIR SITUATIONS, INSERTIONS, SURFACES, AND VARIOUS FORMS.
Folium, the Leaf, is a very general, but not universal, organ of vegetables, of an expanded form, presenting a much greater surface to the atmosphere than all the other parts of the plant together. Its colour is almost universally green, its internal substance pulpy and vascular, sometimes very succulent, and its upper and under surfaces commonly differ in hue, as well as in kind or degree of roughness.
Leaves are eminently ornamental to plants from their pleasing colour, and the infinite variety as well as elegance of their forms. Their many œconomical uses to mankind, and the importance they hold in the scale of nature as furnishing food to the brute creation, are subjects foreign to our present purpose, and need not here be insisted upon. Their essential importance to the plant which bears them, and the curious functions by which they contribute to its health and increase, will presently be detailed at length. We shall first explain their different situations, insertions, forms, and surfaces, which are of the greatest possible use in systematical botany.
The leaves are wanting in many plants, called for that reason plantæ aphyllæ as Salicornia, Engl. Bot. t. 415 and 1691, Stapelia variegata, Curt. Mag. t. 26, glanduliflora, Exot. Bot. t. 71, and all the species of that genus. In such cases the surface of the stem must perform all their necessary functions.
1. With respect to Situation and Position,
Ramea, branch-leaves, sometimes differ from those of the main stem, and then require to be distinguished from them, as Melampyrum arvense, t. 53.
Alterna, alternate leaves, stand solitarily on the stem or branches, spreading in different directions, as those of Borage, t. 36, and innumerable other plants.
Conferta, clustered, or crowded together, as those of Trientalis europæa, t. 15.
Terna, three together, as Verbena triphylla, Curt. Mag. t. 367. The plants of Chili and Peru seem particularly disposed to this arrangement of their leaves. Quaterna, quina, &c. when 4, 5, or more are so situated, as in various species of Heath, Erica.
Verticillata, whorled, is used to express several leaves growing in a circle round the stem, without a reference to their precise number, as in Asperula cynanchica, Engl. Bot. t. 33, and odorata, t. 755, which with the genus Galium, and some others, are for this reason called stellatæ, star-leaved plants. Whorled leaves are also found in Hippuris vulgaris, t. 763, and many besides.
Disticha, two-ranked, spreading in two directions, and yet not regularly opposite at their insertion, as Pinus cariadensis, Lamb. Pin. t. 32, and the Yew, Taxus baccata, Engl. Bot. t. 746.
Secunda, unilateral, or leaning all towards one side, as Convallaria multiflora, t. 279.
Adpressa, close-pressed to the stem, as Xeranthemum sesamoides, Curt. Mag. t. 425.
Verticalia, perpendicular, both sides at right angles with the horizon, as Lactuca Scariola, Engl. Bot. t. 268.
Erecta, upright, forming a very acute angle with the stem, as Juncus articulatus, t. 238.
Patentia, spreading, forming a moderately acute angle with the stem or branch, as Atriplex portulacoides, t. 261.
Horizontalia, horizontal, or patentissima, spreading in the greatest possible degree, as Gentiana campestris, t. 237.
Reclinata, inclining downward, as Leonurus Cardiaca, t. 286.
Obliqua, twisted, so that one part of each leaf is vertical, the other horizontal, as Pritiliaria obliqua, t. 857, and some of the large Proteæ.
Depressa, radical leaves pressed close to the ground, as Plantago media, Engl. Bot. t. 1559, and P. Coronopus, t. 892. The same term applied to stem-leaves, expresses their shape only, as being vertically flattened, in opposition to compressa.
Demersa, immersa, or submersa, plunged under water, as Potamogeton perfoliatum, t. 168, Hottonia palustris, t. 364, Lobelia Dortmanna, t. 140, and the lower leaves of Ranunculus aquatilis, t. 101, while its upper are folia natantia.
Emersa, raised above the water, as the upper leaves, accompanying the flowers, of Myriophyllum verticillatum, t. 218, while its lower ones are demersa.
2. By Insertion is meant the mode in which one part of a plant is connected with another.
Folia petiolata, leaves on footstalks, are such as are furnished with that organ, whether long or short, simple or compound, as Verbascum nigrum, Engl. Bot. t. 59, Thalictrum minus, t. 11, alpinum, t. 262, &c.
Peltata, peltate, when the footstalk is inserted into the middle of the leaf, like the arm of a man holding a shield, as in the Common Nasturtium, Tropæolum majus, Curt. Mag. t. 23, Drosera peltata, Exot. Bot. 41, Cotyledon Umbilicus, Engl. Bot. t. 325, Hydrocolyle vulgaris, t. 751, and the noble Cyamus Nelumbo, Exot. Bot. t. 31, 32.
Connata, connate, united at their base, as Chlora perfoliata, Engl. Bot. t. 60, whose leaves are connato-perfoliata.
Vaginantia, sheathing the stem or each other, as in most grasses; see Phleum alpinum, Engl. Bot. t. 519, and Arundo arenaria, t. 530. The same character is found in many of the Orchis tribe, as Satyrium albidum, t. 505.
Equitantia, equitant, disposed in two opposite rows and clasping each other by their compressed base, as in Narthecium ossifragum, t. 535, and the genus Iris; also Witsenia corymbosa, Exot. Bot. t. 68, and Dilatris corymbosa, t. 16.
Decurrentia, decurrent, running down the stem or branch in a leafy border or wing, as Onopordum Acanthium, Engl. Bot. t. 977, Carduus tenuiflorus, t. 412, and many other Thistles, also the Great Mullein, Verbascum Thapsus, t. 549, and Comfrey, Symphytum officinale, t. 817.
Florifera, flower-bearing, when flowers grow out of the disk or margin of any leaf, as in Ruscus aculeatus, t. 560, Xylophylla latifolia, and X. falcata, Andr. Repos. t. 331. This is equivalent to a frond in the class Cryptogamia; see p. 133.
3. With regard to form, Leaves are either simplicia, simple, like those of Grasses, Orchises, Lilies, and many other plants, as Ballota nigra, Engl. Bot. t. 46, and Berberis vulgaris, t. 49; or composita, compound, as in most Umbelliferous plants, Parsley, Hemlock, &c.; also Roses, Engl. Bot. t. 990—992.
In compound leaves the footstalk is either simple, as in the instances last quoted, and Sium angustifolium, t. 139; or compound, as those of Selinum palustre, t. 229, and Thalictrum majus, t. 611. In simple leaves the footstalk, if present, must of course be simple, while in compound ones it must always be present, though not always subdivided.
Simple Leaves are either integra, undivided, as those of Grasses and Orchises; or lobata, lobed, like the Vine, the Thistle, most kinds of Cranesbill, as Geranium pratense, Engl. Bot. t. 404, &c.
Leaves are frequently undivided and lobed on the same plant, as the Hop, Engl. Bot. t. 427.
4. The following are the moat remarkable forms of Simple Leaves, considering their outline only.
Orbiculatum, a circular or orbicular leaf, whose length and breadth are equal, and the circumference an even circular line. Precise examples of this are scarcely to be found. Some species of Piper approach it, and the leaf of Hedysarum styracifolium is perfectly orbicular, except a notch at the base.
Oblongum, oblong, three or four times longer than broad. This term is used with great latitude, and serves chiefly in a specific character to contrast a leaf which has a variable, or not very decided, form, with others that are precisely round, ovate, linear, &c.
Spatulatum, spatulate, of a roundish figure tapering into an oblong base, as in Silene Otites, Fl. Brit. Engl. Bot. t. 85.
Cuneiforme, wedge-shaped, broad and abrupt at the summit, and tapering down to the base, as in Saxifraga cuneifolia.
Lanceolatum, lanceolate, of a narrow oblong form, tapering towards each end, very common, as Tulipa sylvestris, Engl. Bot. t. 63, Lithospermum purpurocæruleum, t. 117, Plantago lanceolata, t. 507, many Willows, &c.
Acerosum, needle-shaped, linear and evergreen, generally acute and rigid, as in the Fir, Pinus, Juniper, Juniperus communis, t. 1100, and Yew, Taxus baccata, t. 746. Linnæus observes, Phil. Bot. 219, that this kind of leaf has, for the most part, a joint at its union with the branch.
Triangulare, triangular, having three prominent angles, without any reference to their measurement or direction, as in the genus Chenopodium, Cochlearia danica, t. 696, and some leaves of the Ivy.
Quinquangulare, with five angles, as some Ivy leaves, &c.
Deltoides, trowel-shaped or deltoid, having three angles, of which the terminal one is much further from the base than the lateral ones, as Chenopodium Bonus-Henricus, Engl. Bot. t. 1033, and some leaves of Cochlearia danica. A wrong figure is quoted for this in Philosophia Botanica, which has caused much confusion.
Cordatum, heart-shaped, according to the vulgar idea of a heart; that is, ovate hollowed out at the base, as Tamus communis, t. 91.
Lunulatum, crescent-shaped, like a half-moon, whether the points are directed towards the stalk, or from it, as Passiflora lunata, Sm. Ic. Pict. t. 1.
Sometimes the posterior angles are cut off, as in Convolvulus sepium, t. 313.
Hastatum, halberd-shaped, triangular, hollowed out at the base and sides, but with spreading lobes, as Rumex Acetosella, t. 1674, Antirrhinum Elatine, t. 692, and the upper leaves of Solanum Dulcamara, t. 565. Panduriforme, fiddle-shaped, oblong, broad at the two extremities and contracted in the middle, as the Fiddle Dock, Humex pulcher t. 1576.
Runcinatum, runcinate, or lion-toothed, cut into several transverse, acute segments, pointing backwards, as the Dandelion, Leontodon Taraxacum, t. 540.
Lyratum, lyrate, or lyre-shaped, cut into several transverse segments, gradually larger towards the extremity of the leaf, which is rounded, as Erysimum Barbarea, t. 443.
Fissum, cloven, when the margins of the fissures and segments are straight, as in the Gingko-tree, Salisburia adiantifolia.
Bifidum, trifidum, multifidum, &c. express the number of the segments.
Lobatum, lobed, when the margins of the segments are rounded, as in Anemone Hepatica, Curt. Mag. t. 10.
Bilobum, trilobum, &c., according to the number of the lobes.
Sinuatum, sinuated, cut into rounded or wide openings, as Statice sinuata, t. 71, and Virgilia helioides, Exot. Bot. t. 37. Partitum, deeply divided, nearly to the base, as Helleborus viridis, Engl. Bot. t. 200.
Bipartitum, tripartitum, multipartitum, according to the number of the divisions.
Incisum, and Dissectum, cut, are nearly synonymous with the last.
It is remarked by Linnæus that aquatic plants have their lower, and mountainous ones their upper, leaves most divided, by which they better resist the action of the stream in one case, and of wind in the other. Probably these actions are in some measure the causes of such configurations.
Palmatum, palmate, cut into several oblong, nearly equal segments, about half way, or rather more, towards the base, leaving an entire space like the palm of the hand, as Passiflora cœrulea, Curt. Mag. t. 28.
Pinnatifidum, pinnatifid, cut transversely into several oblong parallel segments, as Ipomopsis, Exot. Bot. t. 13, 14, Bunias Cakile, Engl. Bot.]] t. 231, Lepidium didymum, t. 248, petræum, t. 111, and Myriophyllum verticillatum, t. 218.
Pectinatum, pectinate, is a pinnatifid leaf, whose segments are remarkably narrow and parallel, like the teeth of a comb, as the lower leaves of Myriophyllum verticillatum, and those of Hottonia palustris, Engl. Bot. t. 364.
Inæquale, unequal, sometimes called oblique, when the two halves of the leaf are unequal in dimensions, and their bases not parallel, as in Eucalyptus resinifera, Exot. Bot. t. 84, and most of that genus, as well as of Begonia.
5. The Terminations of Leaves are various.
Folium truncatum, an abrupt leaf, has the extremity cut off, as it were, by a transverse line, as Liriodendrum tulipifera, Curt. Mag. t. 275. Præmorsum, jagged-pointed, very blunt, with various irregular notches, as in Dr. Swartz's genus Aërides, comprehended under the Epidendrum of Linnæus. See E. tessellatum, Roxb. Pl. of Coramandel. t. 42, and præmorsum, t. 43.
Retusum, retuse, ending in a broad shallow notch, as Rumex digynus, Engl. Bot. t. 910.
Emarginatum, emarginate, or nicked, having a small acute notch at the summit, as the Bladder Senna, Colutea arborescens, Curt. Mag. t. 81.
Obtusum cum acumine, blunt with a small point, as Statice Limonium, t. 102.
Cirrosum, cirrose, tipped with a tendril, as in Gloriosa superba, Andr. Repos. t. 129.
6. The different Margins of Leaves are characterized as follows.
Folium integerrimum, an entire leaf, as in the Orchis and Lily tribe, as well as Polygala vulgaris, Engl. Bot. t. 76, Daphne Laureola. t. 119, &c.
This term is opposed to all kinds of teeth, notches, or incisions. It regards solely the margin of a leaf; whereas integrum, p. 152, respects its whole shape, and has nothing to do with the margin. English writers who translate the one entire, and the other very entire are therefore incorrect.
Inerme, unarmed, is opposed to spinous.
Ciliatum, fringed, bordered with soft parallel hairs, as Galium cruciatum, Engl. Bot. t. 143.
Cartilagineum, cartilaginous, hard and horny, as Saxifraga callosa, Dicks. Dr. Pl. n. 63.
Dentatum, toothed, beset with projecting, horizontal, rather distant teeth of its own substance, as Atriplex laciniata, Engl. Bot. t. 165, Hypochæris maculata, t. 225, and the lower leaves of Centaurea Cyanus, t. 277; also Nymphæa Lotus, Curt. Mag. t. 797.
Serratum, serrated, when the teeth are sharp, and resemble those of a saw, pointing towards the extremity of the leaf. Examples of this are frequent, as Urtica, t. 148 and 1236, Rosa, t. 992, &c., Comarum palustre, t. 172, and Senecio paludosus, t. 650; also Dillenia indica, Exot. Bot. t. 2. Some leaves are doubly serrated, duplicato-serrata, having a series of smaller serratures intermixed with the larger, as Mespilus grandiflora, t. 18, and Campanula Trachelium, Eng. Bot. t. 12.
Crenatum, notched, or crenate, when the teeth are rounded, and not directed towards either end of the leaf, as in Ground-Ivy, Glechoma hederacea, t. 853, Chrysoplenium, t. 54 and 490, and Sibthorpia europæ, t. 649. In Saxifraga Geum, t. 1561, the leaves are sharply crenate. In the two British species of Salvia, t. 153 and 154, the radical leaves are doubly crenate.
Erosum, jagged, irregularly cut or notched, especially when otherwise divided besides, as in Senecio squalidus, t. 600.
Repandum, wavy, bordered with numerous minute angles, and small segments of circles alternately, as Menyanthes nymphæoides, t. 217, and Inula dysenterica, t. 1115. Glandulosum, glandular, as Hypericum montanum, t. 371, and the Bay-leaved Willow, Salix pentandra.
Linnæus seems originally to have applied this term to the rolling of the whole leaf backwards, as in Solidago Virgaupea, Engl. Bot. t. 301, meaning to use the expression margine revolutum when the margin was intended; but this latter case being extremely frequent and the other very rare, he fell into the practice of using revolutum simply for the margin.
Conduplicatum, folded, when the margins are brought together in a parallel direction, as in Roscoea purpurea, Exot. Bot. t. 108.
7. Terms expressive of different kinds of surface, applying equally to the leaf and to the stem, have been already explained, p. 124. To these may be added the following, chiefly appropriated to leaves.
Punctatum, dotted; either superficially as in Rhododendrum punctatum, Andr. Repos. t. 36, and Melaleuca linarifolia, Exot. Bot. t. 56; or through the substance, as in Hypericum perforatum, Engl. Bot. t. 295, and the whole natural order to which the Orange and Lemon belong.
Rugosum, rugged, when the veins are tighter than the surface between them, causing the latter to swell into little inequalities, as in various species of Sage, Salvia, See Flora Græca; also Teucrium Scorodonia, Engl. Bot. t. 1543.
Bullatum, blistery, is only a greater degree of the last, as in the Garden Cabbage, Brassica oleracea.
Plicatum, plaited, when the disk of the leaf, especially towards the margin, is acutely folded up and down, as in Mallows, and Alchemilla vulgaris, Engl. Bot. t. 597, where, however, the character is but obscurely expressed.
Crispum, curled, when the border of the leaf becomes more expanded than the disk, so as to grow elegantly curled and twisted, which Linnæus considers as a disease. Malva crispa, Ger. em. 931, is an example of it, and may probably be a variety of M. verticillata, Jacq. Hort. Vind. v. 1. t. 40.
Concavum, hollow, depressed in the middle, owing to a tightness in the border, as Cyamus Nelumbo, Exot. Bot. t. 32.
Venosum, veiny, when the vessels by which the leaf is nourished are branched, subdivided, and more or less prominent, forming a network over either or both its surfaces, as Cratægus, or rather Pyrus, torminalis, Engl. Bot. t. 298, and Verbascum Lychnitis, t. 58.
Nervosum, or costatum, ribbed, when they extend in simple lines from the base to the point, as in Cypripedium Calceolus, t. 1, the Convallariæ, t. 279 and 280, Stratiotes alismoides, Exot. Bot. t. 15, and Roxburghia viridiflora, t. 57. The greater clusters of vessels are generally called nervi or costæ, nerves or ribs, and the smaller venæ, veins, whether they are branched and reticulated, or simple and parallel.
Avenium, veinless, and enerve, ribless, are opposed to the former.
Trinerve, three-ribbed, is applied to a leaf that has three ribs all distinct from the very base, as well as unconnected with the margin, in the manner of those many-ribbed leaves just cited, as Blakea trinervis, Curt. Mag. t. 451.
Basi trinerve, three-ribbed at the base, is when the base is cut away close to the lateral ribs, as in Burdock, Arctium Lappa, Engl. Bot. t. 1228, Tussilago, t. 430 and 431, and the great Annual Sunflower.
Triplinerve, triply-ribbed, when a pair of large ribs branch off from the main one above the base, which is the case in many species of Sunflower or Helianthus, Laurus Cinnamomum and Camphora, as well as Blakea triplinervis, Aublet Guian. t. 210.
Coloratum, coloured, expresses any colour in a leaf besides green, as in Arum bicolor, Curt. Mag. t. 820, Amaranthus tricolor, and others of that genus, Justicia picta, Hedysarum pictum, Jacq. Ic. Rar. t. 567, Tradescantia discolor, Sm. Ic. Pict. t. 10, Pulmonaria officinalis, Engl. Bot. t. 118.
Variegatum, variegated, is applied to a sort of variety or disease, by which leaves become irregularly blotched with white or yellow, like those of Striped Grass, Arundo colorata, Fl. Brit.; as also the Elder, the Mentha rotundi folia, Engl. Bot. t. 446, and the Aucuba japonica, which last is not known in our gardens in its natural green state.Nudum, naked, implies that a leaf is destitute of all kinds of clothing or hairiness, as in the genus Orchis. Nudus applied to a stem means that it bears no leaves, and to a flower that it has no calyx.
8. The following terms express the substance, peculiar configuration, or any other remaining circumstances of leaves, not already explained.
Subulatum, awlshaped, tapering from a thickish base to a point, as Salsola Kali, t. 634.
Tubulosum, tubular, hollow within, as Allium Cepa, the Common Onion. The leaf of Lobelia Dortmanna, Engl. Bot. t. 140, is very peculiar in consisting of a double tube.
Carnosum, fleshy, of a thick pulpy substance, as in all those called succulent plants, Crassula lactea, Exot. Bot. t. 33, Aloe, Sedum, Mesembryanthemum, &c. See Sempervivum tectorum, Engl. Bot. t. 1320.
Gibbum, gibbous, swelling on one side or both, from excessive abundance of pulp, as Aloe retusa, Curt. Mag. t. 455.
Compressum, compressed, flattened laterally, as Mesembryanthemum uncinatum, Dill. Elth. t. 193, and acinaciforme, t. 211.
Depressum, depressed, flattened vertically, as M. linguiforme, t. 183—185. See p. 148.
Carinatum, keeled, when the back is longitudinally prominent, as Narcissus biflorus t. 276.
Ensiforme, sword-shaped, is a two-edged leaf, tapering to a point, slightly convex on both surfaces, neither of which can properly be called upper or under, as in most of the genus Iris. See Curt. Mag. t. 671, t. 9, &c., and Fl. Græc. t. 39 and 40.
Anceps, two-edged, is much the same as the last.
Acinaciforme, scimitar-shaped, compressed, with one thick and straight edge, the other thin and curved, as Mesembryanthemum acinaciforme above-mentioned.
Dolabriforme, hatchet-shaped, compressed, with a very prominent dilated keel, and a cylindrical base, as M. dolabriforme, Dill. Elth. t. 191, Curt. Mag. t. 32.
These two last terms might well be spared, as they seem contrived only for the plants in question, and indeed are not essentially distinct from each other.
Trigonum, three-edged, having three longitudinal sides and as many angles, like M. deltoides, Dill. Elth. t. 195, Linn. Phil. Bot. t. 1. f. 58. Linnæus has erroneously referred to this figure to illustrate his term deltoides; misled, as it should seem, by the name of the plant to which it belongs; but his definition is foreign to the purpose, see p. 155, and alludes to the outline of a flat leaf.
Triquetrum differs from trigonum only in being used by Linnæus for a three-sided awl-shaped leaf, as M. emarginatum, Dill. Elth. t. 197, f. 250, and bicolorum, t. 202, also Saxifraga burseriana.
Tetragonum, four-edged, having four prominent angles, as Iris tuberosa, Fl. Græc. t. 41.
Lingulatum, tongue-shaped, of a thick, oblong, blunt figure, generally cartilaginous at the edges, as Mesembryanthemum linguiforme, Dendrobium linguiforme, Exot. Bot. t. 11, and several species of Saxifraga, as S. mutata, Curt. Mag. t. 351, S. Cotyledon, &c.
Coriaceum, leathery, thick, tough and somewhat rigid, as Magnolia grandiflora, and Hydrangea hortensis, Sm. Ic. Pict. t. 12, Curt. Mag. t. 438.
Sempervirens, evergreen,permanent through one, two, or more winters, so that the branches are never stripped, as the Ivy, the Fir, the Cherry Laurel, the Bay, &c.
Deciduum, deciduous, falling off at the approach of winter, as in most European trees and shrubs.
Alienatum, alienated, when the first leaves of a plant give place to others totally different from them and from the natural habit of the genus, as in many Mimosæ of New Holland; see M. verticillata, Curt. Mag. t. 110, and myrtifolia, t. 302; also Lathyrus Nissolia, Engl. Bot. t. 112. The germination of this last plant requires investigation, for if its first leaves be pinnated, which is probable, it is exactly a parallel case with the New Holland Mimosæ.
Appendiculatum, furnished with an additional organ for some particular purpose not essential to a leaf, as Dionæa muscipula, Curt. Mag. t. 785, cultivated very successfully by Mr. Salisbury, at Brompton, whose leaves each terminate in a pair of toothed irritable lobes, that close over and imprison insects; or Nepenthes distillatoria, Rumph. Amboin. v. 5, t. 59, f. 2, the leaf of which bears a covered pitcher, full of water. Aldrovanda vesiculosall, and our Utriculariæ, Engl. Bot. t. 253, 254, have numerous bladders attached to the leaves, which seem to secrete air, and float the plants.
Many of the preceding terms applied to leaves are occasionally combined to express a form between the two, as ovato-lanceolatum, lanceolate inclining to ovate, or elliptico-lanceolatum, as in the Privet, Engl. Bot. t. 764. When shape, or any other character, cannot be precisely defined, sub is prefixed to the term used, as subrotundum, roundish, subsessile, not quite destitute of a footstalk, to which is equivalent subpetiolatum, obscurely stalked. By the judicious use of such means, all necessary precision is attained. It is to be wished that authors were always uniform and consistent, at least with themselves, in the application of terms; but as Linnæus, the father of accurate botanical phraseology, very frequently misapplies his own terms, it is perhaps scarcely to be avoided. I have observed botanists most critical in theory, to be altogether deficient in that characteristic phraseology, that power of defining, which bears the stamp of true genius, and which renders the works of Linnaeus so luminous in despite of incidental errors. Perhaps no mind, though ever so intent on the subject, can retain all the possible terms of description and their various combinations, for ready use at any given moment. There are few natural objects to which a variety of terms are not equally applicable in description, so that no two writers would exactly agree in their use. Neither is Nature herself so constant as not perpetually to elude our most accurate research. Happy is that naturalist who can seize at a glance what is most characteristic and permanent, and define all that is essential, without trusting to fallacious, though ever so specious, distinctions!
9. Folia composita, compound leaves, consist of two or any greater number of foliola, leaflets, connected by a common footstalk.
Folium articiilatum, a jointed leaf, is when one leaflet, or pair of leaflets, grows out of the summit of another, with a sort of joint, as in Fagara tragodes, Jacq. Amer., t. 14. Digitatum, digitate or fingered, when several leaflets proceed from the summit of a common foot-stalk, as Potentilla verna, Engl. Bot. t. 37, reptans, t. 862, and Alchemilla alpina, t. 244.
Binatum, binate, is a fingered leaf consisting of only two leaflets, as in Zygophyllum, Curt. Mag. t. 372.
Pinnatum, pinnate, when several leaflets proceed laterally from one foot-stalk, and imitate a pinnatifid leaf, p. 158. This is of several kinds.
abruptè, abruptly, without either a terminal leaflet or a tendril, as Cassia Chamæcrista, Curt. Mag. t. 107, and the genus Mimosa. See M. pudica, the Common Sensitive-plant. This form of leaf is much more uncommon than the imparipinnatum, and we have no perfect example of it among British plants. The nearest approach to it is the genus Orobus, whose leaves have only the rudiments of a tendril. A truly wonderful variety of the Orobus sylvaticus, Engl. Bot. t. 518, with large simple leaves, has bean found in Wales.
alternatìm, alternately, when they are alternate, as Vicia dumetorum (Cracca sylvatica) Riv. Pent. Irr. t. 51, and occasionally in our V. sativa, lutea, &c.
interruptè, interruptedly, when the principal leaflets are ranged alternately with an intermediate series of smaller ones, as Spiræa Filipendula, Engl. Bot. t. 284, S. Ulmaria t. 960, and Potentilla anserina, t. 861.
articulatè, jointedly, with apparent joints in the common footstalk, as Weinmannia pinnata.
lyrato, in a lyrate manner, having the terminal leaflet largest, and the rest gradually smaller as they approach the base, as Erysimum præcox, t. 1129, and, with intermediate smaller leaflets, Geum rivale, t. 106; also the Common Turnip. Such leaves are usually denominated lyrate in common with those properly so called (whose shape is simple, and not formed of separate leaflets); nor is this from inaccuracy in botanical writers. The reason is, that these two kinds of leaves, however distinct in theory, are of all others most liable to run into each other, even on the same plant, examples of which are frequent in the class Tetradynamia.
verticillato, in a whorted manner, the leaflets cut into fine divaricated segments embracing the footstalk, as Sium verticillatum, Fl. Brit. Engl. Bot. t. 395.
Auriculatum, an auricled leaf, is furnished at its base with a pair of leaflets, properly distinct, but occasionally liable to be joined with it, as Salvia triloba, Fl. Græc. t. 17, and Dipsacus pilosus, Engl. Bot. t. 877. Linnæus in the last example uses the term appendiculatum, which is correct, but superfluous, and I have therefore ventured to apply it somewhat differently, p. 173.
Conjugatum, conjugate, or yoked, consists of only a pair of pinnæ or leaflets, and is much the same as binatum. Instances of it are in the genus Zygophyllum, whose name, equivalent to Yoke-leaf, expresses this very character; also in Lathyrus sylvestris, Engl. Bot. t. 805, and latifolius, t. 1108. Bijugum, trijugum, quadrijugum, multijugum, &c., express particular numbers of pairs of leaflets, and are used for that purpose where such discrimination is requisite for specific characters, as in Mimosæ.
The different degrees in which leaves are compounded are thus distinguished, without any reference to the mode.
Compositum, simply compound, as in the above instances.
Bigeminatum, twice paired, as Mimosa Unguis cati, Plum. Ic. t. 4; and tergeminatum, thrice paired, as M. tergemma; alsoBiternatum, twice ternate, as Ægopodium, Engl. Bot. t. 940; triternatum, thrice ternate, as Fumaria lutea, t. 588; and
Bipinnatum, doubly pinnate, tripinnatum, triply pinnate, of which examples have just been given: all apply to the mode, as well as the degree, in which leaves are compounded.
Pedatum, pedate, is a peculiar kind of leaf, being ternate, with its lateral leaflets compounded in their fore part, as Helleborus fœtidus, Engl. Bot. t. 613, and H. niger, Curt. Mag., t. 8. There is an affinity between a pedate leaf and those simple ones which are three-ribbed at the base, p. 167. See also the disposition of the lateral veins in Aristolochia Clematitis, Engl. Bot. t. 398.
In compounding the foregoing terms we must take care not to express a contradiction. Thus the leaves of many Mimosæ, as the purpurea, Andr. Repos. t. 372, and sensitiva, are conjugate pinnata, conjugate in the first instance, pinnate in the next, not conjugato-pinnata, of an intermediate nature between conjugate and pinnate, which is impossible. Neither are the leaves of Mimosa pudica digitato-pinnata, for there is no medium between the two terms; but they are digitate, or composed of leaflets proceeding from the top of a common foot-stalk, and those leaflets are pinnate. On the other hand ovato-lanceolatum, lanceolate approaching to ovate, or elliptico-lanceolatum, approaching to elliptic, as in the Privet, Engl. Bot. t. 764, whose leaves often assume that shape, are easily understood.