See also:

• PATHOLOGY (from Gr. raBos, suffering)

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)

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

• PHYSICAL

Water. B. Living. See also:

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

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

• INTERNAL

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

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

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)

It should be remembered that a single See also:

• COMPLETE

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

Similarly with See also:

• ANEMONE

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)

If such a general See also:

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

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

• CELLULOSE

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

• PRO

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)

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)

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 obscure, and usually regarded as internal, though experiments go to show that some variegations are infectious. 2. Spotted Leaves, &c.—Discoloured spots or patches on leaves and other herbaceous parts are common symptoms of disease, and often furnish clues to See also:

• IDENTIFICATION (Lat. idem, the same)

Moreover, variegations deceptively like these disease spots are known, e.g. Senecio Kaempferi. Red- spots may indicate the presence of Fungi, e.g. Potystigma, or insects, e.g. Phytoptus. Brown spots are characteristic of Phytophthora, Puccinia, &c., and black ones of Fusicladium, Ustilago, Rhytisma, &c. Both are common as advanced symptoms of destruction by Fungi and insects. Brilliantly coloured spots and patches follow the action of acid fumes on the vegetation near towns and factories, and such parti-coloured leaves often present striking resemblance to autumn foliage. Symptoms of scorching owing to abnormal insolatione.g. in greenhouses where the See also:

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

The injured cells die and turn brown; the living cells beneath grow out, and form cork, and under the released pressure bulge outwards and repeatedly divide, forming a mass of succulent regenerative tissue known as callus. Living cells of the pith, phloem, cortex, &c., may also co-operate in this formation of regenerative tissue, and if the wound is a mere See also:

• KNIFE (0. E. cuff, a word appearing in different forms in many Teutonic languages, cf. Du. knijf, Ger. Kneif, a shoe-maker's knife, Swed. knif; the ultimate origin is unknown; Skeat finds the origin in the root of " nip," formerly " knip "; Fr. canif is a

Excrescences may be divided into those occurring on herbaceous tissues, of which Galls are well-known examples, and those found on the woody stem, branches, &c., and themselves eventually woody, of which Burrs of various kinds afford common illustrations. Among the simplest examples of the former are the hairs which follow the irritation of the cells by mites. These hairs often occur in tufts, and are so coloured and arranged that they were long taken for Fungi and placed in the " genus " Erineum. Cecidia or galls arise by the hypertrophy of the subepidermal cells of a leaf, cortex, &c., which has been pierced by the ovipositor of an insect, and in which the See also:

• EGG (O.E. aeg, cf. Ger. Ei, Swed. aegg, and prob. Gr. u,ov, Lat. ovum)
• EGG, AUGUSTUS LEOPOLD (1816-1863)

In many cases the swellings on leaves are minute, and may be termed pustules—e.g. those due to Synchytrium, Protomyces, Cysto pus, many Ustilagineae, &c. These cases are not easily distinguished superficially from the pustular outgrowth of actual mycelia and spores (stromata) of such Fungi as Nectria, Puccinia, &c. The cylindrical stem-swellings due to Calyptospora, Epichloe; &c., may also be mentioned here, and the tyro may easily confound with these the layers and cushions of eggs laid on similar organs by moths. There is a class of gall-like or pustular outgrowths for which no external cause has as yet been determined, and which are therefore often ascribed to internal causes of disease. Such are the cork-warts on elms, maples, &c., and the class of outgrowths known as Intumescences. Recent researches point to definite external conditions of moisture, affecting the processes of respiration and transpiration, &c., as being responsible for some of these. The " scab " of potatoes is another case in point. Frost blisters are pustular swellings due to the up-growth of callus-tissue into cavities caused by the uprising of the superficial cortex under the action of intense cold. Turning now to outgrowths of a woody nature, the well-known burrs or " knaurs," so common on elms and other trees are cases in point. They are due to some injury—e.g. bruising by a See also:

• CART (A.S. crcet, Gaelic cairt; connected with " car ")

There are many varieties of burrs, though all woody outgrowths of old trees are not to be confounded with them, e.g. the " knees " of Taxodium, &c. Many typical burrs might be described as witches'-brooms, with all the twigs arrested to extremely See also:

• SHORT, FRANCIS JOB (1857– )

Exudations and Rotting.—The outward symptoms of many diseases consist in excessive discharges of moisture, often accompanied by bursting of over-turgid cells, and eventually by putrefactive changes. Conditions of hyper-turgescence are common in herbaceous plants in wet seasons, or when overcrowded and in situations too moist for them. This unhealthy state is frequently combined with etiolation: what is termed rankness is a particular case, and if the factors concerned are removed by drainage, weeding out, See also:

• FREE

Fumago, Antennaria —is not surprising, and the leaves of limes are often black with them. See also:

• FLUX (Lat. fluxus, a flowing; this being also the meaning of the English term in medicine, &c.)

No sharp line can be drawn between these diseases and some of the preceding, inasmuch as it often depends on the external conditions whether necrosis is a dry-rot, in the sense I employ the term here, or a wet-rot, when it would come under the preceding category. The " dying back " of the twigs of trees and shrubs is a frequent case. The cortical tissues gradually shrink and dry up, turning brown and black in patches or all over, and when at length the cambium and medullary See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

7. Monstrosities.—A large class of cases of departure from the normal form, depending on different and often obscure causes, may be grouped together under this heading; most of them arc of the kind termed Teratological, and it is difficult to decide how far they should be regarded as pathological if we insist that a disease threatens the existence of the plant, since many of these malformations—e.g. See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)