See also:

• PATHOLOGY (from Gr. raBos, suffering)

PATHOLOGY OF  See also:

• PLANTS

PLANTS " Phytopathology " or plant See also:

• PATHOLOGY (from Gr. raBos, suffering)

pathology (Gr. dmrov, plant), comprises our knowledge of the symptoms, course, causes and remedies of the maladies which threaten the See also:

• LIFE

life of plants, or which result in abnormalities of structure that are regarded, whether directly injurious or not to life, as unsightly or undesirable . In its systematized See also:

• FORM (Lat. forma)

form, as a See also:

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

branch of botanical study, it is of See also:

• RECENT

recent date, and, as now understood, the subject first received See also:

• SPECIAL

special See also:

• ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention about 185o, when the nature of See also:

• PARASITISM

parasitism began to be intelligible; but many disjointed references to diseased conditions of plants had appeared See also:

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

long before this . The existence of blights and mildews of cereals had been observed and recorded in very See also:

• ANCIENT
• ANCIENT (also spelt ANTIENT; derived, through the Fr. ancien, old, from the late Lat. antianum, from ante, before)

ancient times, as See also:

• WITNESS
• WITNESS (from O. Eng. witan, to know)

witness the See also:

• BIBLE
• BIBLE, ENGLISH

Bible, where See also:

• HALF

half a dozen references to such scourges occur in the Old Testament alone . The epidemic nature of See also:

• WHEAT
• WHEAT (Triticum)

wheat-See also:

• RUST (O.E. rust, a word which appears in -many Teutonic languages, cf. Du. roest, Ger. rost); in origin it is allied with " ruddy " and " red," the reddish-brown powdery substance which forms on the surface of iron or steel exposed to atmospheric corrosio

rust was known to See also:

• ARISTOTLE
• ARISTOTLE (384-322 B.C.)

Aristotle about 350 B.C., and the Greeks and See also:

• ROMANS
• ROMANS, EPISTLE TO THE

Romans knew these epidemics well, their philosophers having shrewd speculations as to causes, while the See also:

• PEOPLE

people held characteristic superstitions regarding them, which found vent in the See also:

• DEDICATION (Lat. dedicatio, from dedicare, to proclaim, to announce)

dedication of special festivals and deities to the pests . See also:

• PLINY, THE ELDER
• PLINY, THE YOUNGER

Pliny knew that flies emerge from See also:

• GALLS

galls . The few records during the See also:

• MIDDLE

middle ages are See also:

• BORNE, KARL LUDWIG (1786–1837)

borne out by what is known of famines and pestilence . See also:

• SHAKESPEARE, WILLIAM (1564-1616)

Shakespeare's reference in See also:

• KING
• KING (O. Eng. cyning, abbreviated into cyng, cing; cf. O. H. G. chun- kuning, chun- kunig, M.H.G. kiinic, kiinec, kiinc, Mod. Ger. Konig, O. Norse konungr, kongr, Swed. konung, kung)
• KING [OF OCKHAM], PETER KING, 1ST BARON (1669-1734)
• KING, CHARLES WILLIAM (1818-1888)
• KING, CLARENCE (1842–1901)
• KING, EDWARD (1612–1637)
• KING, EDWARD (1829–1910)
• KING, HENRY (1591-1669)
• KING, RUFUS (1755–1827)
• KING, THOMAS (1730–1805)
• KING, WILLIAM (1650-1729)
• KING, WILLIAM (1663–1712)

King See also:

• LEAR, EDWARD (1812-1888)

Lear (See also:

• ACT (Lat. actus, actum)

Act HI., sc. iv.) may be quoted as evincing acquaintance with See also:

• MILDEW (0. Eng. meledeaw or mildeaw, explained as " meal-dew," cf. Ger. Me/zit/tau, with more probability, as " honey-dew," Goth. melith, honey, cf. Lat. mel, Gr. µEX)

mildew in the 17th See also:

• CENTURY (from Lat. centuria, a division of a hundred men)

century, as also the interesting See also:

• ROUEN

Rouen 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 Loverdo (166o) . See also:

• MALPIGHI, MARCELLO (1628-1694)

Malpighi in 1679 gave excellent figures and accounts of 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-See also:

• ROLLING

rolling and See also:

• GALL (a word common to many Teutonic languages, cf. Dutch gal, and Ger. Galle; the Indo-European root appears in Gr. xoXi,, and Lat. fel; possibly connected with " yellow," with reference to the colour of bile)
• GALL, FRANZ JOSEPH (1758-1828)

gall See also:

• INSECTS

insects, and See also:

• GREW, NEHEMIAH (1641-1712)

Grew in 1682 equally See also:

• GOOD, JOHN MASON (1764-1827)

good descriptions of a leaf-See also:

• MINING

mining See also:

• CATERPILLAR

caterpillar . During the 18th century more See also:

• ACADEMIC

academic treatment of the subject began to replace the scattered notes . See also:

• HALES, JOHN (1584-1656)
• HALES, or HAYLES, JOHN (d. 1571)
• HALES, STEPHEN (1677-1761)

Hales (1727–1733) discussed the rotting of wounds, cankers, &c., but much had to be done with the See also:

• MICROSCOPE (Gr. µucp6s, small, asenreiv, to %view)

microscope before any real progress was possible, and it is easily intelligible that until the theory of See also:

• NUTRITION

nutrition of the higher plants had been founded by the See also:

• WORK

work of Ingenhouss, See also:

• PRIESTLEY, JOSEPH (1733-1804)

Priestley and De See also:

• SAUSSURE, HORACE BENEDICT DE (1740-1799)
• SAUSSURE, NICOLAS THEODORE DE (1767-1845)

Saussure, the way was not even prepared for accurate knowledge of cryptogamic parasites and the diseases they induce . It was not till De Bary (1866) made known the true nature of parasitic See also:

• FUNGI (p1. of Lat. fungus, a mushroom)

Fungi, based on his researches between 1853-1863, that the vast domain of epidemic diseases of plants was opened up to fruitful investigation, and such See also:

• MODERN

modern See also:

• TREATISES

treatises as those of See also:

• FRANK, JAKOB (1726-1791)

Frank (188o and 1895), Sorauer (1886), Kirchner (189o), were gradually made possible . Plant pathology embraces several branches of study, and may be conveniently divided as follows: I .

The observation and accurate description of symptoms (Diagnosis) . 2 . The study of causes or agencies inducing disease (See also:

• AETIOLOGY, or ETIOLOGY (from Gr. atria, cause, and Xo yia, discourse)

Aetiology) . 3 . The practise of preventive and remedial See also:

• MEASURES

measures (See also:

• THERAPEUTICS (Gr. BepaaeuTLKIi, Sc. TEXVrt, from Beparebsty, to serve)

Therapeutics) . In plants, however, the symptoms of disease are See also:

• APT

apt to exhibit themselves in a very See also:

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

general manner . Our perceptions differentiate but imperfectly symptoms which are due to very different causes and reactions, probably because the organization of the plant is so much less highly specialized than that of higher animals . The yellowing and subsequent casting of leaves, for instance, is a very general symptom of disease in plants, and may be induced by drought, extremes of temperature, insufficient or excessive See also:

• ILLUMINATION

illumination, excess of See also:

• WATER

water at the roots, the See also:

• ACTION

action of parasitic Fungi, insects, See also:

• WORMS

worms, &c., or of poisonous gases, and so forth; and extreme caution is necessary in dealing with See also:

• AMATEUR (Lat. amator, lover)

amateur descriptions of such symptoms, especially when the untrained See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye has taken no cognisance of, or has only vaguely observed, the numerous See also:

• COLLATERAL (from Med. Lat. collateralis,—cum, with, and latus, lateris, side,—side by side, hence parallel or additional)

collateral circumstances of the See also:

• CASE
• CASE, JOHN (d. 1600)

case . The causes of disease may be provisionally classified somewhat as follows, but it may he remarked at the outset that no one of these proximal causes, or agents, is ever solely responsible; and it is very easy to err in attributing a diseased See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition to any of them, unless the relative importance of See also:

• PRIMARY

primary and subordinate agencies is discoverable . For instance, a Fungus epidemic is impossible unless the See also:

• CLIMATIC

climatic conditions are such as to favour the dispersal and germination of the spores; and when plants are killed off owitig to the supersaturation of the See also:

• SOIL

soil with water, it is by no means obvious whether the excess of water and dissolved materials, or the exclusion of See also:

• OXYGEN (symbol 0, atomic weight 16)

oxygen from 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-hairs, or the lowering of the temperature, or the See also:

• ACCUMULATION (from Lat. accumulare, to heap up)

accumulation of foul products of decomposition should be put into the foreground . In every case there are chains of See also:

• CAUSATION

causation concerned,and the same factors will be differently grouped in different cases . Bearing in mind these precautions, we may classify the proximal causal agents of disease as I.—See also:

• EXTERNAL

External agencies .

A . Non-living. b . Non-material . a . Material. i . Temperature . i . See also:

• PHYSICAL

Physical— 2 . Illumination . Soil . 3 . Other agencies .

Water . B . Living . See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

Atmosphere. a . Animals . 2 . Chemical— I . See also:

• VERTEBRATA

Vertebrata . Soil . 2 . Invertebrata . Water. b .

Plants . Atmosphere . i . Phanerogams . 2 . Cryptogams . II.—See also:

• INTERNAL

Internal agencies . While such a See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification may serve its purpose as a sort of See also:

• INDEX

index, it must be confessed that the limits of its usefulness are soon reached . In the first See also:

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

place, the so-called " internal causes " of disease is probably a See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere phrase covering our See also:

• IGNORANCE (Lat. ignorantia, from ignorare, not to know); want of knowledge, a state of mind which in law has important consequences. A well-known legal maxim runs: ignorantia juris non excusat ("ignorance of the law does not excuse")

ignorance of the factors at work, and although a certain convenience attaches to the distinction between those cases where See also:

• TENDER

tender breeds of plants apparently exhibit internal predisposition to suffer more readily than others from parasites, See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

low temperatures, excessive growth, &c.—as is the case with some grafted plants, cultivated hybrids, &c.—the See also:

• MYSTERY (Gr. µw(Trilpcov, from tcuvrm, an initiate, µfew, to shut the mouth)

mystery involved in the phrase " internal causes " only exists until we find what action of the living or non-living environment of the essential mechanism of the plant has upset its See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium . I.—Passing to the recognized external agencies, the physical condition of the soil is a fruitful source of disease . If too closely packed, the soil particles See also:

• PRESENT

present See also:

• MECHANICAL

mechanical obstacles to growth; if too retentive of moisture, the root-hairs suffer, as already hinted; if too open or over-drained, the plant succumbs to drought . All those properties of soil known as texture, porosity, See also:

• DEPTH

depth, inclination to the See also:

• HORIZON (Gr. 6pfTwv, dividing)

horizon, &c., are concerned here .

Many maladies of plants are traceable to the chemical See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition of soils—e.g. deficiency of nutritive salts, especially nitrates and See also:

• PHOSPHATES

phosphates; the presence of poisonous salts of See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron, See also:

• COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper, &c., or (in the soil about the roots of trees in towns) of See also:

• COAL

coal-See also:

• GAS

gas and so forth . But it is worthy of special attention that the mere chemical composition of agricultural and See also:

• GARDEN (from O. Fr. garden, mod. Fr. jardin; this, like our words " garth," a paddock attached to a building, and " yard," comes from a Teutonic word for an enclosure which appears in Gothic as gards and O. H. Ger. gart, cf. Dutch gaarde and Ger. .garten)

garden soils is, as a See also:

• RULE

rule, the least important feature about them, popular See also:

• OPINION (Lat. opinio, from opinari, to think)

opinion to the contrary notwithstanding . See also:

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

Ordinary soils will almost always provide the necessary chemical ingredients if of proper physical texture, depth, &c . (see FUNGI and See also:

• BACTERIOLOGY

BACTERIOLOGY) . As regards water, its deficiency or excess is a relative See also:

• MATTER

matter, and although many of the See also:

• MINOR
• MINOR (Lat. for smaller, lesser)
• MINOR, ROBERT CRANNELL (1839-1904)

minor maladies of pot-plants in windows and greenhouses controlled by amateurs depend on its misuse, water alone is probably never a primary cause of disease . Its over-See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply is, however, a frequent cause of predisposition to the attacks of parasitic Fungi—e.g. the damping off of seedlings—and in saturated soils not only are the roots and root-hairs killed by asphyxiation, but the whole course of soil See also:

• FERMENTATION

fermentation is altered, and it takes See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time to " sweeten " such by draining, because not only must the noxious bodies be gradually washed out and the lost salts restored, but the See also:

• BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi, two, and lanx, a dish or scale)

balance of suitable bacterial and fungal life must be restored . The atmosphere is a cause of disease in the neighbourhood of chemical See also:

• WORKS

works, large towns, volcanoes, &c., in so far as it carries See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid gases and poisons to the leaves and roots; but it is usual to See also:

• ASSOCIATE (Lat. associates, from ad, to, and sociare to join)

associate with it the action of excessive humidity which brings about those tender watery and more or less etiolated conditions which favour parasitic Fungi, and diminish transpiration and there-fore nutrition . It is customary to speak of the disastrous effects of See also:

• COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold winds, See also:

• SNOW (in O. Eng. sndw; a common Indo-European word; cf. in Teutonic languages, Ger. Schnee, Du. sneeuw; in Slavonic snieg', Lith. snegas; Gr. vi4a, Lat. nix, nivis, whence the Romanic forms, Ital. neve, Fr. neige, &c.; Ir. and Gael. sneachd; the original

snow, See also:

• HAIL (O. Eng. kcegl and hagol, 1 cf. the cognate Teutonic hagel, as in German, Dutch, Swedish, &c.; the Gr. K&XX17E, pebble, is probably allied)

hail and See also:

• FROST (a common Teutonic word, cf. Dutch, vorst, Ger. Frost, from the common Teutonic verb meaning " to freeze," Dutch, vriezcn, Ger. frieren; the Indo-European root is seen in Lat. pruina, hoar-frost, cf. prurire, to itch, burn, pruna, burning coal, Sans
• FROST, WILLIAM EDWARD (1810–1877)

frost, See also:

• LIGHTNING

lightning, &c., under the heading of atmospheric influences, which only shows once more how impossible it is to See also:

• SEPARATE

separate causes individually . Turning to the non-material external agents, probably no factors are more responsible for See also:

• ILL

ill-See also:

• HEALTH

health in plants than temperature andlight . Every plant is constrained to carry out its functions of germination, growth, nutrition, See also:

• REPRODUCTION

reproduction, &c., between certain limits of temperature, and somewhere between the extremes of these limits each See also:

• FUNCTION

function finds an optimum temperature at which the working of the living machinery is at its best, and, other things being equal, any See also:

• GREAT

great departure from this may induce pathological conditions; and many disasters are due to the failure to provide such suitable temperatures—e.g. in greenhouses where plants requiring very different optimum temperatures and illumination are kept together . Equally disastrous are those climatic or seasonal changes which involve temperatures in themselves not excessive but in wrong sequence; how many more useful plants could be grown in the open in the See also:

• UNITED

United See also:

• KINGDOM

Kingdom if the deceptively mild springs were not so often followed by frosts in May and See also:

• JUNE

June ! The indirect effects of temperature are also important .

Trees, of which 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 buds are " nipped " by frost, would frequently not suffer material injury, were it not that the small frost-cracks serve as points of entry for Fungi; and numerous cases are known where even high temperatures can be endured on See also:

• RICH, BARNABE (c. 1540-1617)
• RICH, CLAUDIUS JAMES (1787-1821)
• RICH, JOHN (1692-1761)
• RICH, PENELOPE, LADY (c. 1562–1607)
• RICH, RICHARD, 1ST BARON RICH (1490?-1567)

rich, deep, retentive soils by plants which at once succumb to drought on shallow or non-retentive soils . All See also:

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

chlorophyll plants require See also:

• LIGHT

light, but in very different degrees, as exemplified even in the United Kingdom by the shade-bearing See also:

• BEECH

beech and See also:

• YEW (Taxus baccata)

yew contrasted with the light-demanding See also:

• LARCH (from the Ger. Larche, M.H.G. Lerche, Lat. larix)

larch and See also:

• BIRCH
• BIRCH (Betula)
• BIRCH, SAMUEL (1813–1885)
• BIRCH, THOMAS (1705-1766)

birch ; and as with temperature so with light, every plant and even every See also:

• ORGAN

organ has its optimum of illumination . The " See also:

• DRAWN

drawn " or etiolated condition of over-shaded plants is a case in point, though here again the soft, watery plant often really succumbs to other disease agents—e.g. parasitic Fungi—supervening on its non-resistant condition . Animals and plants as agents of disease or injury form See also:

• PART

part of the larger subject of the struggle for existence between living organisms, as is recognized even by those who do not so readily apprehend that diseased conditions in general are always signs of defeat in the struggle for existence between the suffering organism and its environment, living and non-living . The Vertebrata come within the See also:

• SCOPE (through Ital. scopo, aim, purpose, intent, from Gr. o'KOaos, mark to shoot at, aim, o ic07reiv, to see, whence the termination in telescope, microscope, &c.)

scope of our subject, chiefly as destructive agents which cause wounds or devour young shoots and foliage, &c . Rabbits and other burrowing animals injure roots, squirrels and birds snip off buds, horned See also:

• CATTLE (Norman Fr. catel, from Late Lat. capitale, wealth or property, a word applied in the feudal system to movable property and particularly to live stock, and surviving in its wider meaning as " chattel " or " chattle ")

cattle See also:

• STRIP

strip off bark, and so forth . It is among the Invertebrata that epidemics of destruction are referred to, though we should See also:

• BEAR
• BEAR, BLACK
• BEAR, BROWN
• BEAR, GRIZZLY
• BEAR, ISABELLINE
• BEAR, WHITE

bear in mind that it is only the difference in numerical proportion that prevents our speaking of an epidemic of elephants or of rabbits, though we use the See also:

• TERM

term when speaking of blight insects; there is little consistency in the matter, as it is usual to speak of an invasion or See also:

• SCOURGE (Ital. scoriada, from Lat. excoriare, to flay, corium, skin)

scourge of locusts, caterpillars, &c . See also:

• INSECT

Insect injuries are very varied in degree and in See also:

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

kind . Locusts devour all before them; caterpillars defoliate -_ plant, and necessitate the premature utilization of its reserves; other insects (e.g . Grapholitha) eat the buds or the roots (e.g. See also:

• WIRE (A.S. wir, a wire; cf. Swed. vire, to twist, M.H.G. wiere, a gold ornament, Lat. viriae, armlets, ultimately from the root wi, to twist, bind)

wire-worms), and so maim the plant that its foliage suffers from want of water and assimilation is diminished, or actual withering follows . Many See also:

• APHIDES (pl. of Aphis)

aphides, &c., puncture the leaves, suck out the See also:

• SAP

sap, and induce va: ious See also:

• LOCAL

local deformations, See also:

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

arrest of growth, pustular swellings, &c., and if numerous all the evils of defoliation may follow . Others (e.g. miners) See also:

• TUNNEL (Fr. tonne!, later tonneau, a diminutive from Low Lat. tonna, tunna, a tun, cask)

tunnel into the leaf parenchyma, and so put the assimilating areas out of action in another way .

It should be remembered that a single See also:

• COMPLETE

complete defoliation of a herbaceous See also:

• ANNUAL

annual may so incapacitate the assimilation that no stores are available for seeds, tubers, &c., for another See also:

• YEAR

year, or at most so little that feeble plants only come up . In the case of a 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 matters run somewhat differently; most large trees in full foliage have far more assimilatory See also:

• SURFACE

surface than is immediately necessary, and if the injury is confined to a single year it may be a small event in the life of the tree, but if repeated the cambium, bud-stores and fruiting may all suffer . Many larvae of beetles, moths, &c., See also:

• BORE

bore into bark, and injure the cambium, or even 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 and See also:

• PITH (O.E. pitca, cognate with Du. pit, kernel of a nut)

pith; in addition to See also:

• DIRECT

direct injury, the interference with the transpiration current and the See also:

• ACCESS (Lat. accessus)

access of other parasites through the wounds are also to be feared in proportion to the See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers of insects at work . Various local hypertrophies, including galls, result from the increased growth of young tissues irritated by the punctures of insects, or by the presence of eggs or larvae See also:

• LEFT

left behind . They may occur on all parts, buds, leaves, stems or roots, as shown by the numerous See also:

• SPECIES

species of Cynips on See also:

• OAK (O. Eng., (lc)

oak, See also:

• PHYLLOXERA (Gr. 4suXXov, leaf, and Erlpbs, dry)

Phylloxera on vines, &c . The local damage is small, but the general injury to assimilation, absorption and other functions, may be important if the numbers increase . In addition to insects, various kinds of worms, molluscs, &c., are sometimes of importance as pests . The so-called See also:

• EEL

eel-worms (Nematodes) may do immense damage on roots and in the grains of cereals, and every one knows how predatory slugs and snails are . (See ECONOMIC See also:

• ENTOMOLOGY (Gr. iv-roµa, insects, and Xiryos, a discourse)

ENTOMOLOGY.) Plants as agents of damage and disease may be divided into those larger forms which as weeds, epiphytes and so forth, do injury by dominating and shading more delicate species, or by gradually exhausting the soil, &c., and true parasites which actually live on and in the tissues of the plants . It must be remembered that phanerogams also include parasitic species—e.g . Cuscuta, Loranthus, Viscum, Thesium, Rhinanthus, &c.—with various capacities for injury . These enemies are as a rule so conspicuous that we do not look on their depredations as diseases, though the See also:

• GRADUAL (Med. Lat. gradualis, of or belonging to steps or degrees; gradus, step)

gradual deterioration of See also:

• HAY
• HAY (a word common in various forms to Teutonic languages; cf. Ger. Heu, Dutch hooi; the root from which it is derived, meaning " to cut," is also seen in " to hew "; cf. " hoe ")
• HAY, GEORGE (1729—1811)
• HAY, GILBERT
• HAY, JOHN (1838–1905)

hay under the exhausting effects of root-parasites like Rhinanthus, and the onslaught of Cuscuta when unduly abundant, should See also:

• TEACH [THATCH OR THACH], EDWARD (d. 1718)

teach us how unimportant to the See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition the question of See also:

• SIZE

size may be .

It is, however, among the Fungi that we find the most disastrous and elusive agents of disease . Parasitic Fungi may be, as regards their direct action, purely local—e.g . Schinzia, which forms gall-like swellings on the roots of rushes; Gymnosporangium, causing excrescences on See also:

• JUNIPER

juniper stems; numerous leaf Fungi such as Puccinia, Aecidium, Septoria, &c., causing yellow, See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown or See also:

• BLACK
• BLACK, ADAM (1784-1874)
• BLACK, JEREMIAH SULLIVAN (1810–1883)
• BLACK, WILLIAM (1841-1898)

black spots on leaves; or Ustilago in the anthers of certain See also:

• FLOWERS, ARTIFICIAL

flowers . In such cases the immediate damage done may be slight; but the effects of prolonged action and the summation of numerous attacks at numerous points are often enormous, certain of these leaf-diseases costing millions See also:

• STERLING
• STERLING, ANTOINETTE (d. 1904)
• STERLING, JOHN (1806-1844)

sterling annually to some planting and agricultural communities . In other cases the Fungus is virulent and rampant, and, instead of a local effect, exerts a general destructive action throughout the plant--e.g . Pythium, which causes the " damping off " of seedlings, reducing them to a putrid See also:

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

mass in a few See also:

• HOURS, CANONICAL

hours, and Phytophthora, the See also:

• AGENT (from Lat. agere, to act)

agent of the See also:

• POTATO
• POTATO (Solanum tuberosum)

potato disease . Many Fungi, in themselves not very aggressive, slowly bring about important and far-reaching secondary effects . Thus, many Hymenomycetes (Agarics, Polyporei, &c.) live on the wood of trees . This wood is in great part already dead substance, but the mycelium gradually invades the vessels occupied with the transmission of water up the See also:

• TRUNK (Fr. tronc, Lat. truncus, cut off, maimed)

trunk, cuts off the current, and so kills the tree; in other cases such Fungi attack the roots, and so induce rot and See also:

• STARVATION

starvation of oxygen, resulting in " fouling." Numerous Fungi, though conspicuous as parasites, cannot be said to do much individual injury to the See also:

• HOST

host . The extraordinary malformations known as " Witches' Brooms," caused by the repeated branching and tufting of twigs in which the mycelium of Exoascus (on birch) or Aecidium (on See also:

• SILVER

silver See also:

• FIR

fir) are living, may be borne in considerable numbers for years without any very extensive apparent injury to the tree . Again, the curious distortions on the stems of nettles attacked by the Aecidium form of the heteroecious Puccina Caricis (see FUNGI for Heteroecism), or on See also:

• MAIZE, or INDIAN CORN

maize stems and leaves attacked by Ustilago Maydis, or on the inflorescence of crucifers infested with Cystopus, &c., are not individually very destructive; it is the cumulative effects of numerous attacks or of extensive epidemics which eventually tell . Some very curious details are observable in these cases of malformation, For instance, the Aecidium elatinum first referred to causes the new shoots to differ in direction, duration and arrangement, and even shape of foliage leaves from the normal; and the shoots of See also:

• EUPHORBIA

Euphorbia infected with the aecidia of Uromyces Pisi depart so much from the normal in See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance that the attacked plants have been taken for a different species .

Similarly with See also:

• ANEMONE

Anemone infested with Puccinia and Vacciniusn with Calyptospora, and many other cases of deformations due to See also:

• HYPERTROPHY (Gr. inrEp, over, and rpo(A, nourishment)

hypertrophy or See also:

• ATROPHY (Gr. It- priv., rpo4, nourishment)

atrophy . In-stances of what we may term tolerated parasitism, where the host plant seems to accommodate itself very well to the presence of the Fungus, paying the tax it extorts and nevertheless not succumbing but managing to provide itself with sufficient material to go on with, are not rare; and these seem to See also:

• LEAD
• LEAD (pronounced iced)

lead to those cases where the mutual See also:

• ACCOMMODATION (Lat. accommodare, to make fit, from ad, to, cum, with, and modus, measure)

accommodation between host and See also:

• GUEST (a word common to Teutonic languages; cf. Ger. Gast, and Swed. gust; cognate with Lat. hostis, originally a stranger, hence enemy; cf. " host " )
• GUEST, EDWIN (1800–188o)

guest has been carried so far that each derives some benefit from the association—symbiosis (see FUNGI) . II . The kinds of disease due to these various agencies are very different . A plant may be diseased as a whole, because nearly all its tissues are in a morbid or pathological condition, owing to some Fungus pervading the whole—e.g . Pythium in seedlings—or to a See also:

• POISON

poison diffusing from See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell to cell; in the case of unicellular plants—e.g. an alga infested with a Chytridium—indeed, matters can hardly be otherwise . But the case is obviously different where a plant See also:

• DIES, CHRISTOPH ALBERT (1755-1822)

dies because some essential organ or See also:

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

tissue See also:

• TRACT (from Lat. tractare, to treat of a matter, through Provencal tractat and Ital. trattato)

tract has been destroyed, and other parts have suffered because supplies are cut off—e.g. when the upper parts of a tree See also:

• DIE
• DIE (Fr. de, from Lat. datum, given)

die off owing to destruction of the roots, or to the ringing of the See also:

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

stem See also:

• LOWER

lower down; and consequent interference with the transpiration current . In a large number of cases, however, the disease is purely local, and does not itself extend far into the organ or tissue affected . If a mass of living plant-tissue is cut, the first 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 observed is one of See also:

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

colour: the See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white " flesh " of a potato or an See also:

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

apple turns brown as the See also:

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

air enters, and closer examination shows that cell walls and contents are alike affected . The cut cells die, and oxidized products are concerned in the change of colour, the brown juices exuding and soaking into the cell-walls . The next change observable after some hours is that the untouched cells below the cut grow larger, push up the dead surface, and See also:

• DIVIDE

divide by walls tangential to it, with the formation of tabloid See also:

• CORK
• CORK (perhaps through Sp. corcha from Lat. cortex, bark, but possibly connected with quercus, oak)
• CORK, RICHARD BOYLE

cork-cells . The layer of cork thus formed cuts out the dead debris and serves to. protect the uninjured cells below .

Such healing by cork formation is accompanied by a rise of temperature: the active growth of the dividing cells is accompanied by vigorous See also:

• METABOLISM (from Gr. ,uera(3oXh, change)

metabolism and respiration, and a See also:

• STATE
• STATE, GREAT OFFICERS OF

state of " See also:

• WOUND (O. Eng. wund,connected with a Teutonic verb, meaning to strive, fight, suffer, seen in O. Eng. winnan, whence Eng. " win ")

wound See also:

• FEVER (Lat. febris, connected with fervere, to burn)

fever " supervenes until the healing is completed . The phenomena described occur in all cases of cicatrization of wounds in nature—e.g. leaf-tissue, young stems, roots, &c., when cut or pierced by insects, thorns and so forth . They are concerned in the occlusion of broken twigs and of falling leaves, andit is from the actively growing " callus " See also:

• DEVELOPED

developed at the surface of the wounded tissues of cuttings, buddings, prunings, &c., that the healing and .renewal of tissues occur of which See also:

• ADVANTAGE

advantage is taken in the practice of what might well be termed plant See also:

• SURGERY
• SURGERY (Fr. chirurgie, from Gr. Xetpoupyfa, i.e. hand-work)

surgery . A third phenomenon observable in such healing tissues is the increased flow and accumulation of plastic materials at the seat of injury . The enhanced metabolism creates a current of See also:

• DRAUGHT (from the common Teutonic word " to draw "; cf. Ger. 7'racht, load; the pronunciation led to the variant form " draft," now confined to certain specific meanings)

draught on the supplies of available 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-stuffs around . The phenomenon of irritability here concerned is well shown in certain cases where a parasitic organism gains access to a cell—e.g . Pleotrachelus causes the invaded Pilobolus to swell up, and changes the whole course of its cell metabolism, and similarly with Plasmodiophora in the roots of turnips, and many other cases . Irritation and hypertrophy of cells are See also:

• COMMON

common signs of the presence of parasites, as evinced by the numerous malformations, galls, witches'-brooms, &c., on diseased plants . The now well-known fact that small doses of poisonous substances may act as stimuli to living See also:

• PROTOPLASM

protoplasm, and that See also:

• RESPIRATORY

respiratory activity and growth may be accelerated by See also:

• CHLOROFORM (trichlor-methane), CHC13

chloroform, See also:

• ETHER, (C2H5)2O

ether and even powerful See also:

• MINERAL

mineral poisons, such as mercuric chloride, in minimal doses, offers some explanation of these phenomena of hypertrophy, " wound fever," and other responses to the presence of irritating agents . Still further insight is afforded by our increasing knowledge of the enzymes, and it is to be remarked that both poisons and enzymes are very common in just such parasitic Fungi as induce discolorations, hypertrophies and the See also:

• DEATH

death of cells—e.g . See also:

• BOTRYTIS

Botrytis, See also:

• ERGOT, or SPURRED RYE

Ergot, &c . Now it is clear that if an organism gains access to all parts of a plant, and stimulates all or most of its cells to hypertrophy, we may have the latter behaving abnormally—i.e. it maybe diseased through-out; and such actually occurs in the case of Euphorbia pervaded with Uromyces Pisi, the presence of which alters the whole aspect of the host-plant .

If such a general See also:

• PARASITE (From Gr. irapa, beside, Tiros food)

parasite carries its activities farther, every cell may be killed and the plant forthwith destroyed—e.g . Phytophthora in potatoes . If, on the other See also:

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

hand, the irritating agent is local in its action, causing only a few cells to react, we have the various pimples, excrescences, outgrowths, &c., exhibited in such cases as Ustilago Maydis on the maize, various galls, witches'-brooms, &c . It must not be overlooked that the living cells of the plant react upon the parasite as well as to all external agencies, and the nature of disease becomes intelligible only if we bear in mind that it consists in such altered metabolism—deflected See also:

• PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

physiology—as is here implied . The reaction of the cells may be in two directions, moreover . For instance, suppose the effect of a falling temperature is to so modify the metabolism of the cells that they fill up more and more with watery sap; as the freezing-point is reached this may result in destructive changes, and death from cold may result . If, on the contrary, the gradual cooling is met by a corresponding depletion of the cells of water, even intense cold may be sustained without injury . Or. take another case . If the attack of a parasite is met by the formation of some substance in the protoplasm which is chemotactically repulsive to the invader, it may be totally incapable of penetrating the cell, even though equipped with a whole armoury of cytases, diastatic and other enzymes, and poisons which would easily overcome the more passive resistances offered by mere cell-walls and cell-contents of other plants, the protoplasm of which forms bodies chemotactically attractive to the Fungus . The various degrees of parasitism are to a certain extent explained by the foregoing . In 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 that a Fungus may enter a plant, it must be able to overcome not merely the resistance of cell-walls, but that of the living protoplasm; if it cannot do this, it must remain outside as a mere epiphyte, e.g . Fumago, Herpotrichia, &c., or, at most, vegetate in the intercellular spaces and See also:

• ANCHOR (from the Greek ayrcvpa, which Vossius considers is from 6yi17 , a crook or hook)

anchor itself to the cell-walls, e.g .

Trichosphaeria . The inability to enter the cells may be due to the lack of chemotactic bodies, to incapacity to form See also:

• CELLULOSE

cellulose-dissolving enzymes, to the existence in the host-cells of antagonistic bodies which neutralize or destroy the acids, enzymes or poisons formed by the hyphae, or even to the formation and See also:

• EXCRETION (Lat. ex, out of, cernere, cretum, to separate)

excretion of bodies which poison the Fungus . But even when inside it does not follow that the Fungus can kill the cell, and many cases are known where the Fungus can break through the cell's first lines of See also:

• DEFENCE
• DEFENCE (Lat. defendere, to defend)

defence (cell-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 and protoplasmic lining); but the struggle goes on at See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close quarters, and various degrees of hypertrophy, accumulation of plastic bodies or secretions, discolorations, &c., ,indicate the suffering of the still living cell . Finally, cases occur where the invaded cell so adapts itself to the presence of the intruder that life in common—symbiosis—results . The dissemination of plant parasites is favoured by many circumstances not always obvious, whence an air of mystery regarding epidemics was easily created in earlier times . The spores of Rusts, Erysipheae and other Fungi may be conveyed from plant to plant by snails; those of tree-killing polyporei, &c., by mice, rabbits, rats, &c., which rub their See also:

• FUR (connected with O. Fr. forre, a sheath or case; so " an outer covering ")

fur against the hymenophores . Bees carry the spores of Sclerotinia as they do the See also:

• POLLEN, AUGUST (or, as he afterwards called himself, ADOLF) LUDWIG (1794-1855)

pollen of the bilberries, and flies convey the conidia of ergot from See also:

• GRAIN (derived through the French from Lat. granum, seed, from an Aryan root meaning " to wear down," which also appears in the common Teutonic word " corn ")

grain to grain . Insects, indeed, are largely concerned in disseminating Fungi, either on their bodies or via the alimentary See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

canal . Worms bring spores to the surface of soil, ducks and other birds convey them on their muddy feet, and, as is well-known, See also:

• WIND
• WIND (a common Teut. word, cognate with Skt. vats, Lat. ventus, cf. " weather," to be of course distinguished from to " wind," to coil or twist, O.Eng. windan, cf. "wander," "wend," &c.)

wind and other physical agencies are very efficient in dissemination . The part played by See also:

• MAN
• MAN, ISLE OF (anc. Mona)

man also See also:

• COUNTS

counts for much . Gardeners and See also:

• FARM

farm labourers convey spores from one See also:

• BED
• BED (a common Teutonic word, cf. German Bett, probably connected with the Indo-European root bhodh, seen in the Lat. fodere, to dig; so " a dug-out place " for safe resting, or in the same sense as a garden " bed ")

bed or See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field to another; carted soil, manure, &c., may abound in spores of Smuts, Fusarium, Polyporei and in sclerotia; and articles through the See also:

• POST

post and so forth often carry infective spores . Every time a See also:

• CARPENTER, LANT (1780-1840)
• CARPENTER, MIRY (1807-1877)
• CARPENTER, WILLIAM BENJAMIN (1813-1885)

carpenter saws fresh See also:

• TIMBER

timber with a saw recently put through wood attacked with dry-rot, he risks infecting it with the Fungus; and similarly in pruning, in propagating by cuttings, &c .

The annual losses due to epidemic plant diseases attain See also:

• PRO

pro-portions not easily estimated . As regards See also:

• MONEY

money value alone the following figures may serve in See also:

• ILLUSTRATION

illustration . In 1882 the United States was calculated to have lost £40,000,000 to £60,000,000from insect and other pests . The wheat-rust See also:

• COSTS

costs See also:

• AUSTRALIA

Australia £2,000,000 to £3,000,000 annually, and in 1891 alone the loss which See also:

• PRUSSIA
• PRUSSIA (Ger. Preussen; Lat. Borussia)

Prussia suffered from grain-rusts was estimated at £20,000,000 sterling . The terrible losses sustained by whole communities of farmers, planters, foresters, &c., from plant diseases have naturally stimulated the See also:

• SEARCH, or VISIT AND SEARCH

search for remedies, but even now the search is too often conducted in the spirit of the believer in See also:

• QUACK

quack medicines, although the agricultural See also:

• WORLD

world is awakening to the fact that before any measures likely to be successful can be attempted, the whole See also:

• CHAIN (through the O. Fr. citable, chcene, &c., from Lat. catena)

chain of causation of the disease must be investigated . Experience with epidemics, dearly bought in the past, has shown that one fruitful cause is the laying open to the inroads of some Fungus or insect, hitherto leading a quiet endemic life in the See also:

• FIELDS, JAMES THOMAS (1817-1881)

fields and forests, large tracts of its special food, along which it may range rampant without check to its dispersal, nutrition and reproduction . Numerous See also:

• WILD, JONATHAN (c. 1682-1725)

wild hypotheses as to changes in the constitution of the host-plant, leading to supposed vulnerability previously non-existent, would probably never have seen the light had the full significance of the truth been grasped that an epidemic results when the external factors favour a parasite somewhat more than they do the host . It may be that in particular cases particular modes of cultivation disfavour the host; or that the soil, See also:

• CLIMATE

climate or seasons do so; but overwhelming See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence exists to show that the See also:

• PRINCIPAL

principal causes of epidemics reside in circumstances which favour the spread, nutrition and reproduction of the pest, and the See also:

• LESSON (through Fr. lecon from Lat. lectio, reading; legere, to read)

lesson to be learnt is that precautions against the See also:

• ESTABLISHMENT (0. Fr. establissement, Fr. etablissement, late Norm. Fr. establishement, from O. Fr. establir, Fr. etablir, Lat. stabilire, to make stable)

establishment of such favouring conditions must be sought . Nevertheless, epidemics occur, and See also:

• PRACTICAL

practical measures are devised to meet the various cases and to check the ravages already begun . The See also:

• PROCEDURE (Fr. procedure, from Lat. procedere, to go for-ward)

procedure consists in most cases in spraying the affected plants with poisonous solutions or emulsions, or in dusting them with fungicidal or insecticidal powders, or applying the fumes of lethal gases . For the composition of the numerous liquids and powders special works must be consulted, but the following principles apply generally . The poison must not be strong enough to injure the roots, leaves, &c., of the host-plant, or allowed to act long enough to bring about such injury .

Care and intelligence are especially needful with certain insecticides such as poisonous gases, or the operators may suffer . It is worse than useless to apply drastic remedies if the See also:

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

main facts cf the life-See also:

• HISTORY

history of the pest are not known; e.g. the application of ordinary antiseptic powders to leaves inside which a Fungus, such as a Uredo or Ustilago, is growing can only result in failure, and similarly if See also:

• TOBACCO

tobacco fumes, for instance, are applied when the insects concerned are hibernating in the ground beneath . Such applications at the moment when spores are germinating on the leaves, e.g . Peronospora, or to the young mycelia of epiphytic parasites, e.g . Erysiphe, or the steeping in hot water of thoroughly ripe hard grains to which spores are attached, e.g . Ustilago, and filling a greenhouse with hydrocyanic acid gas when young insects are commencing their ravages, e.g . Red-spider—all these and similar procedures timed to,catch the pest at a vulnerable See also:

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

stage are intelligent and profitable prophylactic measures, as has been repeatedly shown . Numerous special methods of preventing the spread of Fungi, or the migrations of insects, or of trapping various animals; of leaving infested ground See also:

• FALLOW

fallow, or of growing another See also:

• CROP (a word common. in various forms, such as Germ. Kropf, to many Teutonic languages for a swelling, excrescence, round head or top of anything; it appears also in Romanic languages derived from Teutonic, in Fr. as troupe, whence the English " crupper "

crop useless to the pest, &c., are also to be found in the practical treatises . More indirect methods, such as the grafting of less resistant scions on more vigorous See also:

• STOCKS

stocks, of raising special See also:

• LATE

late or See also:

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

early varieties by See also:

• CROSSING

crossing or selection, and so on, have also met with ,success; but it must be understood that " resistant " in such cases usually means that some peculiarity of See also:

• QUICK

quick growth, early ripening or other life-feature in the plant is for the time being taken advantage of . Among the most interesting modern means of waging See also:

• WAR
• WAR (O. Eng. werre, Fr. guerre, of Teutonic origin; cf. O.H.G. werran, to confound)

war against epidemic pests is that of introducing other epidemics among the pests themselves—e.g. the infection of rats and mice with disease bacilli, or of locusts with insect-killing Fungi, and signs of the successful carrying out of such measures are not wanting . That the encouragement of insectivorous birds has been profitable is well established, and it is equally well-known that their destruction may lead to disastrous insect plagues . Diseases See also:

• ANTI, or CAMPA

anti Symptoms.—The symptoms of plant diseases are, as already said, apt to be very general in their nature, and are sometimes so vaguely defined that little can be learned from them as to the causes at work .

We may often distinguish between primary symptoms and secondary or subordinatesymptoms, but for the purposes of classification in an See also:

• ARTICLE (from Lat. articulus, a joint)

article of this scope we shall only See also:

• ATTEMPT (Lat. adtemptare, attentare, to try)

attempt to See also:

• GROUP

group the various cases under the more obvious signs of disease exhibited . 1 . Discolorations are among the commonest of all signs that a plant is " sickly " or diseased . The principal symptom may show itself in general pallor, including all cases where the normal healthy 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:

• HUE

hue is replaced by a sickly yellowish hue indicating that the chlorophyll apparatus is deficient . It may be due to insufficient illumination (Etiolation), as seen in geraniums kept in too shaded a situation, and is then accompanied by soft tissues, See also:

• ELONGATION

elongation of internodes, leaves usually reduced in size, &c . The laying of wheat is a particular case . False etiolation may occur from too low a temperature, often seen in young wheat in cold springs . Cases of pallor due to too intense illumination and. destruction of chlorophyll must also be distinguished . See also:

• CHLOROSIS (Gr. xXwpbs, pale green)

Chlorosis is a form of pallor where the chlorophyll remains in See also:

• ABEYANCE (O. Fr. abeance, " gaping")

abeyance owing to a want of iron, and can be cured by adding ferrous salts . Lack of other ingredients may also induce chlorotic conditions . Yellowing is a common sign of water-logged roots, and if accompanied by wilting may be due to drought . Over-transpiration in See also:

• BRIGHT, JOHN (1811-188g)
• BRIGHT, SIR CHARLES TILSTON

bright wintry See also:

• WEATHER (O. Eng. weder; the word is common to Teutonic languages; cf. Du. weder, Dan. veir, Icel. ve8r, and Ger. Wetter and Gewitter, storm; the root is wa- to blow, from which is derived " wind ")

weather, when the roots are not absorbing, often results in yellowing .

In other cases the presence of insects, Fungi or poisons at the roots may be looked for . Albinism, with which variegated foliage may be considered, concerns a different set of causes, still obs