See also:

• LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root seen in Gr. Ma-eta, to See also:

• PEEL
• PEEL, ARTHUR WELLESLEY PEEL, 1ST VISCOUNT (1829- )
• PEEL, SIR ROBERT, BART

peel, See also:

• STRIP

strip)  , the name given in popular See also:

• LANGUAGE (adapted from the Fr. langage, from langue, tongue, Lat. lingua)

language to all the See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green See also:

• EXPANDED

expanded See also:

• ORGANS

organs See also:

• BORNE, KARL LUDWIG (1786–1837)

borne upon an See also:

• AXIS (Lat. for " axle ")

axis, and so applied to similar See also:

• OBJECTS

objects, such as a thin See also:

• SHEET

sheet of See also:

• METAL
• METAL (through Fr. from Lat. metallum, mine, quarry, adapted from Gr. µATaXAov, in the same sense, probably connected with ,ueraAAdv, to search after, explore, µeTa, after, aAAos, other)

metal, a hinged flap of a table, the See also:

• PAGE
• PAGE, THOMAS NELSON (1853- )
• PAGE, WILLIAM (1811-1885)

page of a See also:

• BOOK

book, &c . Investigation has shown that many other parts of a plant which externally appear very different from See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary leaves are, in their essential particulars, very similar to them, and are in fact their morphological equivalents . Such are the scales of a bulb, and the various parts of the See also:

• FLOWER (Lat. flos, floris; Fr. fleur)
• FLOWER, SIB

flower, and assuming that the structure ordinarily termed a See also:

• LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf is the typical See also:

• FORM (Lat. forma)

form, these other structures were designated changed or metamorphosed leaves, a somewhat misleading See also:

• INTERPRETATION (from Lat. interpretari, to expound, explain, inter pres, an agent, go-between, interpreter; inter, between, and the root pret-, possibly connected with that seen either in Greek 4 p4'ew, to speak, or irpa-rrecv, to do)

interpretation . All structures morphologically See also:

• EQUIVALENT

equivalent with the leaf are now included under the See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general See also:

• TERM

term phyllome (leaf-structure) . Leaves are produced as lateral outgrowths of the See also:

• STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem in definite See also:

• SUCCESSION (Lat. successio, from succedere, to follow after)

succession below the See also:

• APEX

apex . This See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character, See also:

• COMMON

common to all leaves, distinguishes them from other organs . In the higher See also:

• PLANTS

plants we can easily recognize the distinction between stem and leaf . Amongst the See also:

• LOWER

lower plants, however, it is found that a demarcation into stem and leaf is impossible, but that there is a structure which partakes of the characters of both—such is a thallus . The leaves always arise from the See also:

• OUTER

outer portion of the See also:

• PRIMARY

primary See also:

• MERISTEM (Gr. Aquas-6s, divided or divisible)

meristem of the plant, and the tissues of the leaf are continuous with those of the stem . Every leaf originates See also:

• ASA

asa See also:

• SIMPLE

simple cellular papilla (fig I), which consists of a development from the cortical layers covered by epidermis; and as growth proceeds, the fibro-vascular bundles of the stem are continued outwards, and finally expand and terminate in the leaf . The increase in length of the leaf by growth at the apex is usually of a limited nature . In some ferns, however, there seems to be a See also:

• PROVISION (Lat. provisio)

provision for indefinite terminal growth, while in others this growth is periodically in- terrupted .

It not unfrequently happens, especially amongst Monocotyledons, that after growth at the apex has ceased, it is continued at the See also:

• BASE

base of the leaf, and in this way the length may be much in-creased . Amongst See also:

• DICOTYLEDONS

Dicotyledons this is very rare . In all cases the dimensions of the leaf are enlarged by interstitial growth of its parts . The simplest leaf is found in some mosses, where it consists of a single layer of cells . The typical foliage leaf consists of several layers, and amongst vascular plants is distin- guishable into an outer layer (epidermis) and a central See also:

• TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue (parenchyma) with fibro-vascular bundles distributed through it . The epidermis (fig . 2, es, ei), composed of cells more or less compressed, has usually a different structure and aspect on the two surfaces of the leaf . The cells of the epidermis are very closely See also:

• UNITED

united laterally and contain no green colouring See also:

• MATTER

matter (See also:

• CHLOROPHYLL (from Gr. XAwpos, green, 4bXXov, a leaf)

chlorophyll) except in the pair of cells—guard-cells—which See also:

• BOUND, or BOUNDARY (from O. Fr. bonde, Med. Lat. bodena or butina, a frontier line)

bound the stomata . The outer See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall, especially of the upper epidermis, has a tough outer layer or cuticle which renders it impervious to See also:

• WATER

water . The epidermis is continuous except es where stomata or spaces bounded by specialized as' cells communicate with intercellular spaces in in-the interior of the leaf . It is chiefly on the epi- - dermis of the lower sur- _ See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face (fig . 2, ei) that - stomata, st, are produced, and it is there also that hairs, p, usually " occur .

The lower epidermis is often of a dull or See also:

• PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

pale-green See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour, soft and easily detached . The upper epidermis is frequently smooth and shining, and sometimes becomes very hard and dense . Many tropical plants See also:

• PRESENT

present on the upper See also:

• SURFACE

surface of their leaves several layers of compressed cells beneath the epidermis which serve for storage of water and are known as aqueous tissue . In Structure From Strasburger's Lehrbuch der Botanik by of leaves. permission of Gustav See also:

• FISCHER
• FISCHER, EMIL (1852– )
• FISCHER, ERNST KUNO BERTHOLD (1824–1907)

Fischer . e), U st 1 s ! dicular to the surface . es, Upper epidermis . ei, Lower epidermis . p, Hairs . st, Stomata . ps, Upper (palisade) layers of parenchy matous cells . Lower (spongy) layers of parenchymatous cells .

m, See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

Air-spaces connected with stomata . 1, Air-spaces between the loose cells in the leaves which See also:

• FLOAT (in O. Eng. floc and flota, in the verbal form f eotan; the Teutonic root is flut-, another form of flu-, seen in " flow," cf. " fleet "; the root is seen in Gr. a-M e, to sail, Lat. pluere, to rain; the Lat, fluere and fluctus, wave, is not connect

float upon spongy parenchyma . the surface of the water, fv, Bundles of fibro-vascular tissue . as those of the water-See also:

• LILY

lily, the upper epidermis alone possesses' stomata . The parenchyma of the leaf is the cellular tissue enclosed within the epidermis and surrounding the vessels (fig . 2, ps, pi) . It is known as mesophyll, and is formed of two distinct See also:

• SERIES (a Latin word from serere, to join)

series of cells, each containing the green chlorophyll-granules, but differing in form and arrangement . Below the epidermis of the upper See also:

• SIDE
• SIDE (mod. Eski Adalia)

side of the leaf there are one or two layers of cells, elongated at right angles to the leaf surface (fig . 2, ps), and applied so closely to each other as to leave pi, only small intercellular spaces, except where stomata happen to be present (fig . 2, m) ; they form the palisade tissue . On the other side of the leaf the cells are irregular, often branched, and are arranged more or less horizontally (fig . 2, pi), leaving air-spaces between them, 1, which communicate with stomata; on this See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account the tissue has received the name of spongy .

In leaves having a very See also:

• FIRM

firm texture, as those of Coniferae and Cycadaceae, the cells of the parenchyma immediately beneath the epidermis are very much thickened and elongated in a direction parallel to the surface of the leaf, so as to be fibre-like . These constitute a hypodermal layer, beneath which the chlorophyll cells of the parenchyma are densely packed together, and are elongated in a direction See also:

• VERTICAL (from Lat. vertex, highest point)

vertical to the surface of the leaf, forming the palisade tissue . The form and arrangement of the cells, however, depend much on the nature of the plant, and its exposure to See also:

• LIGHT

light and air . Sometimes the arrangement of the cells on both sides of the leaf is similar, as occurs in leaves which have their edges presented to the See also:

• SKY (M. Eng. skie, cloud; O. Eng. skua, shade; connected with an Indo-European root sku, cover, whence " scum," Lat. obscurus, dark, &c.)

sky . In very succulent plants the cells form a compact See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass, and those in the centre are often colourless . In some cases the cellular tissue is deficient at certain points, giving rise to distinct holes in the leaf, as in Monstera Adansonii . The fibro-vascular See also:

• SYSTEM

system in the leaf constitutes the venation . The fibro-vascular bundles from the stem See also:

• BEND

bend out into the leaf, and are there arranged in a definite manner . In See also:

• SKELETON

skeleton leaves, or leaves in which the parenchyma is removed, this arrangement is well seen . In some leaves, as in the See also:

• BARBERRY (Berberis vulgaris)

barberry, the See also:

• VEINS

veins are hardened, producing spines without any parenchyma . The hardening of the extremities of the fibro-vascular tissue is the cause of the spiny margin of many leaves, such as the See also:

• HOLLY (Ilex Aquifolium)

holly, of the See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

sharp-pointed leaves of See also:

• MADDER

madder, and of mucronate leaves, or those having a See also:

• BLUNT, JOHN HENRY (1823–1884)
• BLUNT, JOHN JAMES (1794–1855)
• BLUNT, WILFRID SCAWEN (184o— )

blunt end with a hard See also:

• PROJECTION

projection in the centre . The form and arrangement of the parts of a typical foliage leaf are intimately associated with the See also:

• PART

part played by, the leaf in the See also:

• LIFE

life of the plant .

The See also:

• FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat surface is spread to allow the maximum amount of sunlight to fall upon it, as it is by the absorption of See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy from the See also:

• SUN
• SUN (0. Eng. sonne, Ger. sonne. Fr. soleil, Lat. sol, Gr. ijXior, from which comes helio- in various English compounds)

sun's rays by means of the chlorophyll contained in the cells of the leaf that the See also:

• BUILDING

building up of plant See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

food is rendered possible; this See also:

• PROCESS

process is known as photo-See also:

• SYNTHESIS (Gr. a6vOeacs, from avvrcBivac, to put together)

synthesis; the first See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage is the See also:

• COMBINATION (Lat. combinare, to combine)

combination of See also:

• CARBON (symbol C, atomic weight 12)

carbon dioxide, absorbed from the air taken in through the stomata into the living cells of the leaf, with water which is brought into the leaf by the See also:

• WOOD, ANTHONY A2 (1632-1695)
• WOOD, JOHN GEORGE (1827—1889)
• WOOD, MRS HENRY [ELLEN] (1814—1887)
• WOOD, SEARLES VALENTINE (1798—188o)

wood-vessels . The wood-vessels form part of the fibro-vascular bundles or veins of the leaf and are continuous throughout the leaf-stalk and stem with the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root by which water is absorbed from the See also:

• SOIL

soil . The palisade layers of the mesophyll contain the larger number of chlorophyll grains (or corpuscles) while the absorption of carbon dioxide is carried on chiefly through the lower epidermis which is generally much richer in stomata . The water taken up by the root from the soil contains nitrogenous and See also:

• MINERAL

mineral salts which combine with the first See also:

• PRO

pro-duct of photo-synthesis—a See also:

• CARBOHYDRATE

carbohydrate--to form more complicated See also:

• NITROGEN [symbol N., atomic weight 14.01, 0=16]

nitrogen-containing food substances of a proteid nature; these are then distributed by, other elements of the vascular bundles (the phloem) through the leaf to the stem and so throughout the plant to wherever growth or development is going on . A large proportion of the water which ascends to the leaf acts merely as a See also:

• CARRIER
• CARRIER, JEAN BAPTISTE (1956-1794)

carrier for the other raw food materials and is got rid of from the leaf in the form of water vapour through the stomata—this process is known as transpiration . Hence the extended surface of the leaf exposing a large See also:

• AREA

area to light and air is eminently adapted for the carrying out.of the process of photo-synthesis and transpiration . The arrangement of the leaves on the stem and branches (see Phyllotaxy, below) is such as to prevent the upper leaves shading the lower, and the shape of the leaf serves towards the same end—the disposition of leaves on a See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch or stem is often seen to form a " See also:

• MOSAIC (corresponding to Lat. opus musivum, from Gr. µovoeiov, an artificial grotto often decorated with mosaics; the word is only found in the sense of mosaic in late Greek, which generally uses k oXI yrlµa)

mosaic," each leaf fitting into the space between neighbouring leaves and the branch on which they are borne without overlapping . Submerged leaves, or leaves which are See also:

• DEVELOPED

developed under water, differ in structure from aerial leaves . They have usually no fibro-vascular system, but consist of a congeries of cells, which sometimes become elongated and compressed so as to resemble veins . They have a layer of compact cells on their surface, but no true epidermis, and no stomafa . Their See also:

• INTERNAL

internal structure consists of cells, disposed irregularly, and sometimes leaving spaces which are filled with air for the purpose of floating the leaf . When exposed to the air these leaves easily part with their moisture, and become shrivelled and dry .

In some cases thereis only a network of filament-like cells, the spaces between which are not filled with parenchyma, giving a skeleton See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance to the leaf, as in Ouvirandra fenestralis (Lattice plant) . A leaf, whether aerial or submerged, generally consists of a flat expanded portion, called the blade, or lamina, of a narrower portion called the petiole or stalk, and sometimes of a portion at the base of the petiole, which forms a sheath or vagina (fig . 5, s), or is developed in the form of outgrowths, called stipules (fig . 24, s) . All these portions are not always present . The sheathing or stipulary portion is frequently wanting . When a leaf has a distinct stalk it is petiolate; when it has none, it is sessile, and if in this See also:

• CASE
• CASE, JOHN (d. 1600)

case it embraces the stem it is said to be amplexicaul . The part of the leaf next the petiole or the axis is the base, while the opposite extremity is the apex . The leaf is usually flattened and expanded horizontally, i.e. at right angles to the See also:

• LONGITUDINAL

longitudinal axis of the shoot, so that the upper face is directed towards the heavens, and the lower towards the See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth . In some cases leaves, as in See also:

• IRIS

Iris, or leaf-like petioles, as in Australian . acacias and eucalypti, have their See also:

• PLANE

plane of expansion parallel to the axis of the shoot, there is then no distinction into an upper and a lower face, but the two sides are developed alike; or the leaf may have a cylindrical or polyhedral form, as in mesembryanthemum . The upper See also:

• ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

angle formed between the leaf and the stem is called its axil; it is there that leaf-buds are normally developed . The leaf is sometimes articulated with the stem, and when it falls off a scar remains; at other times it is continuous with it, and then decays, while still attached to the axis .

In their See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

early See also:

• STATE
• STATE, GREAT OFFICERS OF

state all leaves are continuous with the stem, and it is only in their after growth that articulations are formed . When leaves fall off annually they are called See also:

• DECIDUOUS (from Lat. decidere, to fall down)

deciduous; when they remain for two or more years they are persistent, and the plant is See also:

• EVERGREEN

evergreen . The laminar portion of a leaf is occasionally articulated with the petiole, as in the See also:

• ORANGE
• ORANGE (Citrus Aurantium)
• ORANGE, HOUSE OF

orange, and a See also:

• JOINT (through Fr. from Lat. junctum, jungere, to join)

joint at times exists between the vaginal or stipulary portion and the petiole . The arrangement of the fibro-vascular system in the lamina constitutes the venation or nervation . In an ordinary leaf, as that of the See also:

• ELM

elm, there is observed a large central vein See also:

• RUNNING

running venation. from the base to the apex of the leaf, this is the midrib (fig . 3) ; it gives off veins laterally (primary veins) . A leaf with only a single midrib is said to be unicostate and the venation is described as pinnate or See also:

• FEATHER (0. Eng. (ether, Ger. Feder, from an Indo-European root seen also in Gr. lrrepov, and aEreo-Oat, to fly)

feather-veined . In some cases, as sycamore or See also:

• CASTOR

castor oil (fig . 4), in See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place of there being only a single midrib there are several large veins (ribs) of nearly equal See also:

• SIZE

size, which diverge from the point where the blade joins the petiole or stem, giving off lateral veins . The leaf in this case is multicostate and the venation palmate . The primary veins give off secondary veins, and these in their turn give off See also:

• TERTIARY

tertiary veins, and so on until a See also:

• COMPLETE

complete network of vessels is produced, and those veins usually project on the under surface of the leaf . To a See also:

• DISTRIBUTION (Lat. distribuere, to deal out)

distribution of veins such as this the name of reticulated or netted venation has been applied .

In the leaves of some plants there exists a midrib with large veins running nearly parallel to it from the base to the apex of the lamina, as in See also:

• GRASSES

grasses (fig . 5); or with veins diverging from the base of the lamina in more or less parallel lines, as in See also:

• FAN (Lat. vannus; Fr. eventail)

fan palms (fig . 6), or with veins coming off from it throughout its whole course, and running parallel to each other in a straight or curved direction towards the margin of the leaf, as in See also:

• PLANTAIN (Lat. plantago)

plantain and See also:

• BANANA

banana . In these cases the veins are often united by See also:

• CROSS

cross veinlets, which do not, however, form an angular network . Such leaves are said to be parallel-veined . The leaves of Mono- cotyledons have generally this See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of venation, while reticulated venation most usually occurs amongst Dicotyledons . Some plants, which in most points of their struc- See also:

• TURE

ture are monocotyledonous, yet have reticulated venation ; as in Smilax and Dioscorea . In vascular acotyle- donous plants there is frequently a tendency to See also:

• FORK (Lat. furca)

fork exhibited by the fibro-vascular bundles in the leaf; and when this is the case we have fork-veined leaves . This is well seen in many ferns . The distribution of the system of vessels in the leaf is (Poa) with leaf . The sheaths (Chamaerops), showing the veins ending in a process 1, called running from the base to the See also:

• MAR, EARLDOM OF
• MAR, JOHN ERSKINE, 1ST OR 6TH EARL OF (d. 1572)
• MAR, JOHN ERSKINE, 2ND OR 7TH EARL
• MAR, JOHN ERSKINE, 6TH OR 11TH EARL OF (1675-1732)

mar-a ligule; the blade of the See also:

• GIN

gin, and not forming an angular leaf, f, network, usually easily traced, but in the case of succulent plants, as Hoya, See also:

• AGAVE

agave, stonecrop and mesembryanthemum, the veins are obscure . The See also:

• FUNCTION

function of the veins which consist of vessels and See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres is to form a rigid framework for the leaf and to conduct liquids .

In all plants, except Thallophytes, leaves are present at some See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period of their existence . In Cuscuta (See also:

• DODDER (Frisian dodd, a bunch; Dutch dot, ravelled thread)

Dodder) (q.v.), however, we have an exception . The forms assumed by leaves vary much, not only in different plants, but in the same plant . It is only amongst the lower classes of plants—Mosses, Characeae, &c.—that all the leaves on a plant are similar . As we pass up the See also:

• SCALE
• SCALE (1) A

scale of plant life we find them becoming more and more variable . The structures in ordinary language designated as leaves are considered so See also:

• PAR (Lat. par, equal)

par excellence, and they are frequently spoken of as foliage leaves . In relation to their See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production on the stem we may observe that when they are small they are always produced in See also:

• GREAT

great number, and as they increase in size their number diminishes correspondingly . The cellular process from the axis which develops into a leaf is simple and undivided; it rarely remains so, but in progress of growth becomes segmented in various ways, either longitudinally or laterally, or in both ways . By longitudinal segmentation we have a leaf formed consisting of sheath, stalk and blade; or one or other of these may be absent, and thus stalked, sessile, sheathing, &c., leaves are produced . Lateral segmentation affects the lamina, producing indentations, lobings or fissuring of its margins . In this way two marked forms of leaf are produced—(I) Simple form, in which the segmentation, however deeply it extends into the lamina, does not See also:

• SEPARATE

separate portions of the lamina which become articulated with the midrib or petiole; and (2) See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

Compound form, where portions of the lamina are separated as detached leaflets, which become articulated with the midrib or petiole . In both simple and compound leaves, according to the amount of segmentation and the mode of development of the parenchyma and direction of the fibro-vascular bundles, many forms are produced .

Simple Leaves,—When the parenchyma is developed symmetrically on each side of the midrib or stalk, the leaf is equal; if otherwise, Simple the leaf is unequal or oblique (fig . 3) . If the margins are leaves. even and present no divisions, the leaf is entire (fig . 7) ; if there are slight projections which are more or less pointed, the leaf is dentate or toothed; when the projections See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

lie regularly over each other, like the See also:

• TEETH (O.E. Eel); plural of tooth, O.E. top)

teeth of a saw, the leaf is serrate (fig . 3); when they are rounded the leaf is crenate . If the divisions extend more deeply into the lamina than the margin, the leaf receives different names according to the nature of the segments; thus, when the divisions extend about See also:

• HALF

half-way down (fig . 8), it is cleft; when the divisions extend nearly to the base or to the, midrib the leaf is partite . If these divisions take place in a simple feather-veined leaf it becomes either pinnatifid (fig . 9), when the segments extend to about the See also:

• MIDDLE

middle, or pinnatipartite, when the divisions extend nearly to the midrib . These primary divisions may be again subdivided in a similar manner, and thus a feather-veined leaf will become bipinnatifid or bipinnatipartite; still further subdivisions give origin to tripinnatifid and laciniated leaves . The same kinds of divisions taking place in a simple leaf with palmate or radiating venation, give origin to lobed, cleft and partite forms . The name palmate or palmatifid (fig .

4) is the general term applied to leaves with radiating venation, in which there are several lobes united by a broad expansion of parenchyma, like the See also:

• PALM (Lat. palma, Gr. iraX6.jn )
• PALM, JOHANN PHILIPP (1768-1806)

palm of the See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, as in the sycamore, castor-oil plant, &c . The divisions of leaves with radiating venation may extend to near the base of the leaf, and the names See also:

• BIPARTITE (from the Lat. bi-, two, and partire, to divide)

bipartite, tripartite, quinquepartite, &c., are given according as the partitions are two, three, five or more . The term dissected is applied to leaves with radiating venation, having numerous narrow divisions, as in See also:

• GERANIUM

Geranium See also:

• DISSECTION (from Lat. dissecare, to cut apart)

dissection . When in a radiating leaf there are three primary partitions, and the two lateral lobes are again cleft, as in See also:

• HELLEBORE

hellebore (fig . I I), the leaf is called pedate or pedatifid, from a fancied resem- blance to the claw of a See also:

• BIRD

bird . In all the instances already alluded to the leaves have been considered as flat expansions, in which the ribs or veins spread out on the same plane with the stalk . In some cases, however, the veins spread at right angles to the stalk, forming a peltale leaf as in See also:

• INDIAN

Indian See also:

• CRESS

cress (fig . 12) . The form of the leaf shows a very great variety ranging from the narrow linear form with parallel sides, as in grasses or the See also:

• NEEDLE (O. Eng. ncedl; the word appears in various forms in Teutonic languages, Ger. Nadel, Dutch naal, the root being ne-, to sew, cf. Ger. nahen, and probably Lat. nere, to spin, Gr. vi)ats, spinning)

needle-like leaves of pines and firs to more or less rounded or orbicular—descrip• tions of these will be found in See also:

• WORKS

works on descriptive See also:

• BOTANY (from Gr. l3or6v17, plant; ,66vicety, to graze)

botany—a few examples are illustrated here (See also:

• FIGS

figs . 7, 13, 14, 15) . The apex also varies considerably, being rounded, or obtuse, sharp or acute (fig . 7), notched (fig .

15), &c . Similarly the shape of the base may vary, when rounded lobes are formed, as in See also:

• DOG

dog-See also:

• VIOLET

violet, the leaf is cordate or See also:

• HEART
• HEART, LUNG

heart-shaped ; or See also:

• KIDNEY

kidney-shaped or reniform (fig . 16), when the apex is rounded as in ground See also:

• IVY (A.S. ifig, Ger. Epheu, perhaps connected with apium, anent)

ivy . When the lobes are prolonged down-wards and are acute, the leaf is sagittate (fig . 17) ; when they proceed at right angles, as in Rumex Acetosella, the leaf is hastate or See also:

• HALBERT, HALBERD

halbert-shaped . When a simple leaf is divided at the base into two leaf-like appendages, it is called auriculate . When the development of parenchyma is such that it more than fills up the spaces between the veins, the margins become wavy, crisp or undulated, as in Rumex crispus and Rheum undulatum . By cultivation the cellular tissue is often much increased, giving rise to the curled leaves of greens, savoys, cresses, See also:

• LETTUCE

lettuce, &c . Compound leaves are those in which the divisions extend to the Compound midrib or petiole, and the sepa- mp rated portions become each artileaves . culated with it, and receive the name of leaflets . The midrib, or petiole, has thus the appearance of a branch with (Tropaeolum majus) . See also:

• SENNA (Arab. sand)

Senna .

separate leaves attached to it, but it is considered properly as one leaf, because in its earliest state it arises from the axis as a single piece, and its subsequent divisions in the form of leaflets are all in one plane . The leaflets are either sessile (fig . 18) or have stalks, called petiolules (fig . 19) . Compound leaves are pinnate (fig . 19) or palmate (fig . 18) according to the arrangement of leaflets . When a pinnate leaf ends in a pair of pinnae it is equally or abruptly pinnate (paripinnate) ; when there is a single terminal leaflet (fig . 19), the leaf is unequally pinnate (imparipinnate) ; when the leaflets or pinnae are placed alternately on either side of the midrib, and not directly'opposite to each other, the leaf is alternately pinnate; and when the pinnae are of different sizes, the leaf is interruptedly pinnate . When the See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

division is carried into the second degree, and the pinnae of a compound leaf are themselves pinnately compound, a bipinnate leaf is formed . The petiole or leaf-stalk is the part which unites the See also:

• LIMB

limb or blade of the leaf to the stem . It is absent in sessile leaves, and this is also Petiole. frequently the case when a sheath is present, as in grasses (fig .

5) . It consists of the fibro-vascular bundles with a varying'amount of cellular tissue . When the vascular bundles reach the base of the lamina they separate and spread out in various ways, as already described under venation . The lower part of the petiole is often swollen (fig . 20, p), forming the pulvinus, formed of cellular tissue, the cells of which exhibit the phenomenon of irritability . In See also:

• MIMOSA (so named from the movements of the leaves in many species which " mimic " animal sensibility)

Mimosa pudica (fig . 20) a sensitiveness is located in the pulvinus which upon irritation induces a depression of the whole bipinnate leaf, a similar See also:

• PROPERTY

property exists in the pulvini at the base of the leaflets which See also:

• FOLD

fold upwards . The petiole varies in length, being usually shorter than the lamina, but sometimes much longer . In somepalms it is 15 or 20 ft. See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long, and is so firm as to be used for poles or walking-sticks . In general, the petiole is more or less rounded in its form, the upper surface being flattened or grooved . Sometimes it is compressed laterally, as in the See also:

• ASPEN

aspen, and to this peculiarity the trembling of the leaves of this See also:

• TREE (0. Eng. treo, treow, cf. Dan. tree, Swed. Odd, tree, trd, timber; allied forms are found in Russ. drevo, Gr. opus, oak, and 36pv, spear, Welsh derw, Irish darog, oak, and Skr. dare, wood)
• TREE, SIR HERBERT BEERBOHM (1853- )

tree is due . In aquatic plants the leaf-stalk is sometimes distended with air, as in Pontederia and Trapa, so as to float the leaf .

At other times it is winged, and is either leafy, as in the orange (fig . 21, p), See also:

• LEMON
• LEMON, MARK (1809-1870)

lemon and Dionaea, or See also:

• PITCHER

pitcher-like, as in See also:

• SARRACENIA

Sarracenia (fig . 22) . In some Australian acacias, and in some See also:

• SPECIES

species of See also:

• OXALIS

Oxalis and Bupleurum, the petiole is flattened in a vertical direction, the vascular bundles separating immediately after quitting the stem and running nearly parallel from base to apex . This kind of petiole (fig . 23, p) has been called a phyllode . In these plants the laminae or See also:

• BLADES, WILLIAM (1824-1890)

blades of the leaves are pinnate or bipinnate, and are produced at the leaf of the See also:

• HORSE (a word common to Teutonic languages in such forms as hors, hros, ros; cf. the Ger. ross)

Horse-See also:

• CHESTNUT (nux Castanea)

chestnut (Aes- base of the leaf the spiny culus Hippocastanum). stipules are seen. t extremities of the phyllodes in a See also:

• HORIZONTAL

horizontal direction; but in many instances they are not developed, and the phyllode serves the purpose of a leaf . These phyllodes, by their vertical position and their See also:

• PECULIAR

peculiar form, give a remarkable aspect to vegetation . On the same See also:

• ACACIA

acacia there occur leaves with the petiole and lamina perfect; others having the petiole slightly expanded or winged, and the lamina imperfectly developed; and others in which there is no lamina, and the petiole becomes large and broad . Some petioles are long, slender and sensitive to contact, and function as tendrils by means of which the plant climbs; as in the nasturtiums (Tropaeolum), See also:

• CLEMATIS

clematis and `c others; and in compound leaves the midrib and some of the leaf lets may similarly be transformed into tendrils, as in the See also:

• PEA (Pisum)

pea and See also:

• VETCH

vetch . The leaf base is often developed as a sheath (vagina), which embraces FIG . 2o.-Branch and leaves of the Sensitive plant the whole or part (Mimosa pudica), showing the petiole in its erect of the circumfer- state, a, and in its depressed state, b; also the ence of the stem leaflets closed, c, and the leaflets expanded, d. shg- 5). comes Irritability resides in the pulvinus, p .

paratively rare in dicotyledons, but is seen in umbelliferous plants . It is much more common amongst monocotyledons . In sedges the sheath forms a complete investment of the stem, whilst in Leaf base. grasses it is split on one side . In the latter plants there is also a membranous outgrowth, the ligule, at right angles to the median plane of the leaf from the point where the sheath passes into the lamina, there being no petiole (fig . 5, l) . In leaves in which no sheath is produced we not infrequently find small foliar organs, stipules, at the base of the petiole (fig . 24, s) . The stipules are generally two in number, and they are important as supplying characters in certain natural orders . Thus they occur in the pea and See also:

• BEAN (a common Teutonic word, cf. Ger. Bohne)

bean See also:

• FAMILY

family, in rosaceous plants and the family See also:

• RUBIACEAE

Rubiaceae . They are not common in dicotyledons with opposite leaves . Plants having stipules are called stipulate; those having none are exstipulate . Stipules may be large or small, entire or divided, deciduous or persistent .

They are not usually of the same form as the ordinary foliage leaves of the plant, from which they are distinguished by their lateral position at the base of the petiole . In the See also:

• PANSY, or HEARTSEASE

pansy (fig . 24) the true leaves are stalked and crenate, while the stipules s are large, sessile and See also:

• PIN (a doublet with " pen " from Lat. pinna, feather, pinnacle, which is said to contain the same root as irirvs, pine tree, and properly to mean a sharp point or end)

pin- natifid . In Lathyrus Aphaca and some other plants the true pinnate leaves are abortive, the petiole forms a tendril, and the stipules alone are developed, perform- See also:

• ING

ing the See also:

• OFFICE (from Lat. officium, " duty," " service," a shortened form of opifacium, from facere, " to do," and either the stem of opes, " wealth," " aid," or opus, " work ")

office of leaves . When sti- pulate leaves are op- posite to each other, at the same height on the stem, it occa- to the lamina 1. from the petiole, which terpetiolary or inter- is prolonged. foliar stipule, as in members of the family Rubiaceae . In the case of alternate leaves, the stipules at the base of each leaf are sometimes united to the petiole and to each other, so as to form an adnate, adherent or petiolary stipule, as in the See also:

• ROSE
• ROSE (Rosa)
• ROSE, GEORGE (1744-1818)
• ROSE, HUGH JAMES (1795—1838)
• ROSE, WILLIAM STEWART (1775-1843)

rose, or an axillary stipule, as in Houttuynia cordata . In other in-stances the stipules unite together on the side of the stem opposite the leaf forming an ocrea, as in the See also:

• DOCK

dock family (fig . 25) . In the development of the leaf the stipules frequently See also:

• PLAY

play a most important part . They begin to be formed after the origin of the leaves, but grow much more rapidly than the leaves, and in this way they See also:

• ARCH
• ARCH, JOSEPH (1826– )

arch over the See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

young leaves and form protective See also:

• CHAMBERS (the Fr. chambre, from Lat. camera, a room)
• CHAMBERS, EPHRAIM (d. 1740)
• CHAMBERS, GEORGE (1803-1840)
• CHAMBERS, ROBERT (18oz-1871)
• CHAMBERS, SIR WILLIAM (1726-1796)

chambers wherein the parts of the leaf may develop . In the figs, See also:

• MAGNOLIA

magnolia and pondweeds they are very large and completely envelop the young leaf-bud . The stipules are sometimes so See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute as to be scarcely distinguish-able without the aid of a See also:

• LENS
• LENS (from Lat. lens, lentil, on account of the similarity of the form of a lens to that of a lentil seed)

lens, and so fugacious as to be visible only in the very young state of the leaf .

They may assume a hard and spiny character, as in See also:

• ROBINIA

Robinia Pseud-acacia (fig . 19), or may be cirrose, as in Smilax, where each stipule is represented by a tendril . At the base of the leaflets of a compound leaf, small stipules (stipels) are occasionally produced . See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

Variations in the structure and forms of leaves and leaf-ModiNca- stalks are produced Hons . by the increased development of cel- lular tissue, by the See also:

• ABORTION (from Lat. aboriri, to fail to be born, or perish)

abortion or degeneration of parts, by the multiplication or repetition of parts and by See also:

• ADHESION (from Lat. adhaerere, to adhere)

adhesion . When cellular tissue is developed to a great extent, leaves become succulent and occasionally assume a crisp or curled ap- pearance . Such changes take place naturally, but they are often increased by the See also:

• ART

art of the gardener, and the See also:

• OBJECT

object of many horticultural operations is to increase the bulk and suc- culence of leaves . It is in this way that cabbages and savoys are rendered more delicate and nutritious . By a deficiency in development of parenchyma and an increase in the See also:

• MECHANICAL

mechanical tissue, leaves are liable to become hardened and spinescent . The leaves of barberry and of some species of Astragalus, and the stipules of the false acacia (Robinia) are spiny . To the same cause is due the spiny margin of the holly-leaf . When two lobes at the base of a leaf are prolonged beyond the stem and unite (fig .

26), the leaf is perfoliate, the stem appearing to pass through it, as in Bupleurum perfoliatum and Chlora perfoliata; when two leaves unite by their bases they become connate (fig . 27), as in Lonicera Caprifolium; and when leaves adhere to the stem, forming a sort of winged or leafy ap- pendage, they are decurrent, as in thistles . The formation of peltate leaves has been traced to the See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union of the lobes of a cleft leaf . In the leaf of the See also:

• VICTORIA
• VICTORIA (or VITTORIA), TOMMASSO LUDOVICO DA (C. I540-C. 1613)
• VICTORIA [ALEXANDRINA VICTORIA]

Victoria regia the transformation may be traced during germination . The first leaves produced by the young plant are linear, the second are sagittate and hastate, the third are rounded-cordate and the next are orbicular . The cleft indicating the union of the lobes remains in the large leaves . The parts of the leaf are frequently transformed into tendrils, with the view of enabling the plants to twine See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round others for support . In Leguminous plants (the pea tribe) the pinnae are frequently modified to form tendrils, as in Lathyrus A phaca, in which the stipules perform the function of true leaves . In Flagellaria indica, See also:

• GLORIOSA

Gloriosa superba The two lobes at the base FIG . 27.-Connate leaves of of the leaf are united, so a species of See also:

• HONEYSUCKLE (Mid. Eng., honysocle, i.e. any plant from which honey may be sucked,—cf. A.-S. huni-suge, privet; Ger. Geissblalt; Fr. chevrefeuille)

Honeysuckle that the stalk appears to (Lonicera Caprifolium) . Two come through the leaf. leaves are united by their bases. and others, the midrib of the leaf ends in a tendril . In Smilax there are two stipulary tendrils .

The vascular bundles and cellular tissue are sometimes developed in such a way as to form a circle, with a hollow in the centre, and thus give rise to what are called fistular or hollow leaves, as in the See also:

• ONION (Fr. oignon, Lat. unio, liberally unity, oneness, applied to a large pearl and to a species of onion)

onion, and to ascidia or pitchers . Pitchers are formed either by petioles or by laminae, and they are composed of one or more leaves . In Sarracenia (fig . 22) and Heliamphora the pitcher is composed of the petiole of the leaf . In the pitcher plant, See also:

• NEPENTHES (Gr. vrl7revOis, sc. Q,&puaeov, a drug that takes away grief, from vrl- privative, and 7rivOos, " grief ")

Nepenthes, the pitcher is a modification of the lamina, the petiole often plays the part of a tendril, while the leaf base is flat and leaf-like (fig . 28) . In Utricularia See also:

• BLADDER (from A.S. blaeddre, connected with bl¢wan, to blow, cf. Ger. blase)

bladder-like sacs are formed by a modification of leaflets on the sub-merged leaves . In some cases the leaves are reduced to See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere scales—cetaphyllary leaves; they are produced abundantly upon underground shoots . In parasites (Lathraea, Orobanche) and in plants growing on decaying See also:

• VEGETABLE

vegetable matter (saprophytes), in which no chlorophyll is formed, these scales are the only leaves produced . In Pinus the only leaves FIG . 28.—Pitcher produced on the See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main stem and the lateral of a species of shoots are scales, the acicular leaves of the pitcher-plant (Neptree growing from axillary shoots . In Cycas enthes distillatoria) .

whorls of scales alternate with large pinnate leaves . In many plants, as already noticed, phyllodia or stipules perform the function of leaves . The production of leaf-buds from pules. o, Ocrea . PhYila~ the See also:

• PRIMROSE

primrose, are called See also:

• RADICAL (Lat. radix, a root)

radical ; those on the stem are taxis . cauline; on flower-stalks, floral leaves (see FLOWER) . The first leaves developed are known as See also:

• SEED (from the root seen in Lat. serere, to sow)

seed leaves or cotyledons . The arrangement of the leaves on the axis and its appendages is called phyllotaxis . In their arrangement leaves follow a definite See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order . The points on the stem at which leaves appear are called nodes; the part of the stem between the nodes is the internode . When two leaves are produced at the same See also:

• NODE (Lat. nodus, a loop)

node, one on each side of the stem or axis, and at the same level, they are opposite (fig . 29); when more than two are produced they are verticillate, and the circle of leaves is then called a verticil or whorl . When leaves are opposite, each successive pair may be placed at right angles to the pair immediately preceding .

They are then said to decus- sate, following thus a See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

law of See also:

• ALTERNATION (from Lat. alternare, to do by turns)

alternation (fig . 29) . The same occurs in the verticillate arrangement, the leaves of each whorl rarely being super- posed on those of the whorl next it, but usually alterna- ting so that each leaf in a whorl occupies the space be- tween two leaves of the whorl next to it . There are See also:

• CON

con- siderable irregularities, how- ever, in this respect, and the number of leaves in different whorls is not always See also:

• UNIFORM

uniform, as may be seen in Lysimachia vulgaris . When a single leaf is produced at a node, and the nodes are separated so that each leaf is placed at a different height on the stem, the leaves are alternate (fig . 30) . A plane passing through the point of insertion of the leaf in the node, dividing the leaf into similar halves, is the median plane of the leaf ; and when the leaves are arranged alternately on an axis so that their median planes coincide they form a straight See also:

• ROW, JOHN (c. 1525—1580)

row or orthostichy . On every axis there are usually two or more orthostichies . In fig . 31, leaf 1 arises from a node n; leaf 2 is separated from it by an internode as, and is placed to the right or See also:

• LEFT

left; while leaf 3 is situated directly above leaf I . In this case, then, there are two orthostichies, and the arrangement is said to be distichous . When the See also:

• FOURTH

fourth leaf is directly above the first, the arrangement is tristichous .

The same arrangement continues throughout the branch, so that in the latter case the 7th leaf is above the 4th, the loth above the 7th; also the 5th above the 2nd, the 6th above the 3rd and so on . The size of the angle between the median planes of two consecutive leaves in an alternate arrangement is their divergence; and it is expressed in fractions of the circum- ference of the axis which is supposed to be a circle . In a regularly- formed straight branch covered with leaves, if a See also:

• THREAD (0. Eng. praed, literally, that which is twisted, prawan, to twist, to throw, cf. " throwster," a silk-winder, Ger. drehen, to twist, turn, Du. draad, Ger. Draht, thread, wire)

thread is passed from one to the other, turning always in the same direction, a See also:

• SPIRAL

spiral is described, and a certain number of leaves and of complete turns occur before reaching the leaf directly above that from which the enumeration commenced . If this arrangement is expressed by a fraction, the numerator of which indicates the number of turns, and the denominator the number of internodes in the spiral See also:

• CYCLE
• CYCLE (Gr. KUK)^os, a circle)

cycle, the fraction will be found to represent the angle of divergence of the consecutive leaves on the axis . Thus, in fig . 32, a, b, the cycle con- sists of five leaves, the 61h leaf being placed vertically over the 1st, the 7th over the and and so on; while the number of turns between the 1st and 6th leaf is two; hence this arrangement is indicated by the fraction 1 . In other words, the distance or divergence between the first and second leaf, expressed in parts of a circle, is 1- of a circle or 360° X1 =144° . In fig . 31, a, b, the spiral is ; i.e. one turn and two leaves; the third leaf being placed vertically over the first, and the divergence between the first and second leaf being one-half the circumference of a circle, 36o°X =180° . Again, in a tristichous arrangement the number is 3, or one turn and three leaves, the angular divergence being 120° . . By this means we have a convenient mode of expressing on See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

paper the exact position of the leaves upon an axis . And ,in many cases such a mode of expression is of excellent service in enabling us readily to understand the relations of the leaves .

The divergences may also be represented diagrammatically on a horizontal projection of the vertical axis, as in fig . 33 . Here the outer-most circle represents a See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section of that portion of the axis bearing the lowest leaf, the inner-most represents the highest . The broad dark lines represent the leaves, and they are numbered according to their See also:

• AGE (Fr. age, through late Lat. aetaticum, from aetas)

age and position . It will be seen at once that the leaves are arranged in orthostichies marked I.-V., and that these See also:

• DIVIDE

divide the circumference into five equal portions . But the divergence between leaf 1 and leaf 2 is equal to 1ths of the circumference, and the same is the case between 2 and 3, 3 and 4, &c . The divergence, then, is ~-, and from this we learn that, starting from any leaf on the axis, we must pass twice'round the stem in a spiral through five leaves before reaching one directly over that with which we started . The See also:

• LINE

line which, winding round an axis either to the right or to the left, passes through the points of insertion of all the leaves on the axis is termed the genetic or generating spiral; and that margin of each leaf which is towards the direction from which the spiral proceeds is the kathodic side, the other margin facing the point whither the spiral passes being the anodic side . In cases where the internodes are very See also:

• SHORT, FRANCIS JOB (1857– )

short and the leaves are closely applied to each other, as in the See also:

• HOUSE
• HOUSE (O. Eng. hiss, a word common to Teutonic languages, cf. Dut. huis, Ger. Haus; in Gothic it is only found in gudhiss, a temple; it may be ultimately connected with the root of " hide," conceal)

house-See also:

• LEEK

leek, it is difficult to trace the generating spiral . Thus, in fig . 34 there are thirteen leaves which are numbered in their order, and five turns of the spiral marked by circles in the centre (A indicating the arrangement) ; but this could not be detected at once . So also in See also:

• FIR

fir cones (fig .

35), which are composed of scales or modified leaves, the generating spiral cannot be determined easily . But in such cases a series of secondary spirals or parastichies are seen running parallel with each other *both b right and left, which to a certain FIG . 32.-Part of a branch of a extent conceal the genetic spiral . See also:

• CHERRY

Cherry with six leaves, the See also:

• SIXTH

sixth The spiral is not always con- being placed vertically over the stant throughout the whole first, after two turns of the spiral. length of an axis . The angle of This is expressed by two-fifths. divergence may alter either a, The branch, with the leaves abruptly or gradually, and the numbered in order; b, a magrified phyllotaxis thus becomes very See also:

• REPRESENTATION

representation of the branch, complicated . This See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change may showing the points of insertion of be brought about by See also:

• ARREST (Fr. arrester, arreeter, to stop or stay)

arrest of the leaves and their spiral arrange-development, by increased de- ment . velopment of parts or by a tor- See also:

• SION [Ger. Sitten]

sion of the axis . The former are exemplified in many See also:

• CRASSULACEAE

Crassulaceae and aloes . The latter is seen well in the See also:

• SCREW (O.E. scrue, from O. Fr. escroue, mod. ecrou; ultimate origin uncertain; the word, or a similar one, appears in Teutonic languages, cf. Ger. Schraube, Dan. skrue, but Skeat, following Diaz, finds the origin in Lat. scrobs, a ditch, hole, particularl

screw-See also:

• PINE (Lat. Pinus, Gr. srlrur)

pine (Pandanus) . In the bud of the screw-pine the leaves are arranged in three orthostichies with the phyllotaxis 3, but by torsion the developed leaves become arranged in three strong spiral rows running round the stem . These causes of change in phyllotaxis are also well exemplified in the alteration of an opposite or verticillate arrangement to an alternate, and See also:

• VICE

vice versa; thus the effect of interruption of growth, in causing alternate leaves to become opposite and verticillate, can be distinctly shown in See also:

• RHODODENDRON

Rhododendron ponticum . The See also:

• PRIMITIVE

primitive or generating spiral may leaves sometimes occurs as in Bryophyllum, and many plants of the order Gesneraceae .

The leaf of See also:

• VENUS

Venus's See also:

• FLY (formed on the root of the supposed original Tent. fleugan, to fly)

fly-See also:

• TRAP (0. Eng. treppe or traepee, properly a step, as that or which an animal places its foot and is caught, cf. Ger. Treppe flight of stairs)

trap (Dionaea muscipula) when cut off and placed in See also:

• DAMP

damp See also:

• MOSS

moss, with a See also:

• PAN (" pasturer ")
• PAN (common in various forms to many Teutonic languages, cf. Ger. Pfanne; it is generally taken to be an early adaptation in a shortened form of Lat. patina, shallow bowl or dish, from patere, to lie open)

pan of water underneath and a See also:

• BELL
• BELL, ALEXANDER MELVILLE (1819—1905)
• BELL, ANDREW (1753—1832)
• BELL, GEORGE JOSEPH (1770-1843)
• BELL, HENRY (1767-1830)
• BELL, HENRY GLASSFORD (1803-1874)
• BELL, JACOB (1810-1859)
• BELL, JOHN (1691-178o)
• BELL, JOHN (1763-1820)
• BELL, JOHN (1797-1869)
• BELL, ROBERT (1800-1867)
• BELL, SIR CHARLES (1774—1842)

bell-See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

glass for a See also:

• COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover, has produced buds from which young plants were obtained . Some species of See also:

• SAXIFRAGE (Saxifraga)

saxifrage and of ferns also produce buds on their leaves and fronds . In Nymphaea micrantha buds appear at the upper part of the petiole . Leaves occupy various positions on the stem and branches, and have received different names according to their situation . Thus leaves arising from the See also:

• CROWN

crown of the root, as in a pass either from right to left or from left to right . It sometimes follows a different direction in the branches from that pursued in the stem . When it follows the same course in the stem and branches, they are homodromous; when the direction differs, they are heterodromous . In different species of the same genus the phyllotaxis frequently varies: All modifications of leaves follow the same See also:

• LAWS

laws of arrangement as true leaves—a fact which is of importance in a morphological point of view . In dicotyledonous plants the first leaves produced (the cotyledons) are opposite . This arrangement often continues during the life of the plant, but at other times it changes, passing into distichous and spiral forms . Some tribes of plants are distinguished by their opposite or ver- ticillate, others by their alternate, leaves . Labiate plants have decussate leaves, while 13oragin- aceae have alternate leaves, and Tiliaceae usul[ ally have distichous leaves; Rubiaceae have opposite leaves .

Such arrangements as i, ei ~g and -28 are common in Dicotyledons . The first of these, called a See also:

• QUIN, JAMES (1693—1766)

quin- cunx, is met with in the See also:

• APPLE (a common Teut. word, A.S. aepl, aeppel, O.H.G. aphul, aphal, apfal, mod. Ger. Apfel)

apple, See also:

• PEAR (Pyrus communis)

pear and cherry (fig . 32); the second, in the See also:

• BAY

bay, holly, Plantago See also:

• MEDIA

media; the third, in the cones of Picea See also:

• ALBA

alba (fig . FIG . 33.-See also:

• DIAGRAM

Diagram of a phyllotaxis repre- 35) ; and the fourth in sented by the fraction *. those of the See also:

• SILVER

silver fir . In monocotyledonous plants there is only one seed-leaf or cotyledon, and hence the arrangement is at first alternate; and it generally continues so more or less, rarely being verticillate . Such arrangements as z, and s are common in Monocotyledons, as in grasses, sedges and lilies . It has been found in general that, while the number 5 occurs in the phyllotaxis of Dicotyledons, 3 is common in that of Mono-cotyledons . In the axil of previously formed leaves leaf-buds arise . These leaf-buds contain the rudiments of a shoot, and consist of leaves covering a growing point . The buds of trees of temperate climates, which lie dormant during the See also:

• WINTER, JOHN STRANGE
• WINTER, PETER (c. 1755-1825)

winter, are protected by scale leaves . These scales or protective appendages of the bud consist either of by the fraction laths. right to left .

the altered laminae or of the enlarged petiolary sheath, or of stipules, as in the fig and magnolia, or of one or two of these parts combined . These are often of a coarse nature, serving a temporary purpose, and then falling off when the leaf is expanded . They are frequently covered with a resinous matter, as in See also:

• BALSAM (from Gr. f &X raµov, through Lat. balsamum, contracted by popular use to O. Fr. basme, mod. Fr. bdme; Eng. balm)

balsam-