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We have seen that the principal characters of a plant can be comprehended in the essential and differential characters. But, as these contain only such peculiarities as are supposed to be most essential, a great number of circumstances are omitted from them which, in the view of the botanist drawing them up, may appear unessential, but which to another may seem of the first importance. On this account, a plant cannot be considered completely known until a full description of every part shall have been obtained. In this description every circumstance connected with the external or internal organisation should be included, and a full statement made of all the peculiarities of every part, however obscure or difficult to observe. It is upon descriptions of this kind that systematic botany is based. Essential and differential characters are only relative to the degree of knowledge of the person who prepares them: a description is independent of all relative knowledge; it exhibits a plant as it actually is, without reference to its resemblances or differences. The former are adapted to the state of knowledge of a particular era; the latter, if complete, to that of all eras.
Notwithstanding their importance, descriptions of this kind are very rare: they occupy too much space in books to be inserted conveniently; they are difficult to draw up; and it seldom happens that an observer has the means of describing every part of a plant: the root, or the fruit, or the flower, or some other part, is probably not to be procured; and this renders a description, even in the best hands, necessarily imperfect.
In drawing up a description, care must be taken that every term is used in its strict sense; that all is perspicuous and free from ambiguity; and that the different parts are described in
their just order, beginning with the root, and ending with the fruit. The following is the form in which a perfect description would be prepared: it shows the order in which the different parts are spoken of, and the points of structure to which it is desirable to advert. The student will do well to consult it carefully: he should take common plants, the descriptions of which he can find in books, and, for the sake of exercise, describe them himself according to this form; comparing them afterwards with the printed descriptions of botanists. A number of the points which I think it necessary to describe are usually overlooked by others, as unimportant, or as too difficult to ascertain : these I have marked with an asterisk; so that those points which are commonly adverted to may be distinguished from those that are usually omitted :—
Root. Its figure, quality, substance, duration, and *anatomical internal analysis.
Stem. Its figure, direction, duration, articulation, ramification, size, surface, and * internal analysis.
Leaves. Their * vernation, * internal structure, figure, articulation, insertion, margin, surface, venation, direction, colour, texture, and size.
Petiole. Its form, surface, and the proportion it bears to the leaf.
Stipule. Their position, texture, surface, insertion, duration, figure, and proportion to the petiole.
Inflorescence. Its nature, order of developement, ramification, position, and proportion to the leaves.
Bracteæ. Their numbers, figure, station, proportion to the adjacent parts, surface, texture, * venation.
Flowers. Their order and time of expansion.
Calyx. Its structure, figure, station with respect to the ovary and the axis of inflorescence, surface, æstivation, odour, size, proportion to the corolla, colour, and venation.
Corolla. Its structure, figure, station with respect to the ovary and axis of inflorescence and adjacent parts, surface, æstivation, size, colour, proportion to the calyx and stamens, and venation. Stamens. Their number, direction, æstivation, station with respect to the petals, insertion, proportion to the ovarium and corolla; whether separate, or combined in several parcels; whether in one series or several, of equal or unequal length. Filaments, their form, length, and surface. Anthers, their mode of insertion on the filament; dehiscence with respect to the axis, whether inwards or outwards, and, with respect to themselves, whether transversely or longitudinally, by pores, or otherwise; their form ; * structure of the endothecium ; surface, colour, size; the proportion they bear to the size of the filaments, the number of their valves, the nature of the connectivum.
Pollen. Its colour, form, size, surface; whether distinct or cohering; and * mode of bursting.
Disk. If present, its size, figure, texture, and station.
Ovary. Its apparent, as well as theoretical, structure ; the position of its carpels with respect to the organs around it; its surface; mode of division; number of ribs, if any; veins; cells. Ovules, their number; insertion upon the placenta; position with respect to the axis of the ovary; the situation of their foramen. Styles, their number, length, figure, surface, direction, and proportion. Stigmas, their number, form, and surface.
Fruit. Its texture, form; whether naked, or covered by the remains of the floral envelopes; whether sessile or stipitate; mode of dehiscence, if any; number of its valves and cells; situation of the placentæ; nature of its axis; number of its seeds.
Seed. Its position with respect to the axis of the fruit, mode of insertion, form, surface; the texture and nature of the testa, aril, and other appendages, if any; * position of the raphe and chalaza. Albumen, its texture, if any. Embryo, its direction; position with respect to the axis of the fruit, to the bilum of the seed, and to the albumen ; the proportion it bears to the mass of the latter; the form of its cotyledons and radicle; * its mode of germination.
The medical and economical qualities.
The points in which it agrees or disagrees with other species.
Descriptions, it must be observed, are of two kinds, collective and specific: the former explaining minutely the characters common to several species, as in an order or a genus ; the latter, the character of one species only. The difference between these two, and the manner of applying each of them, will be best understood by the following examples.
The following mode of fully describing an order is taken from Adolphe Brongniart's excellent memoir on RhamNEÆ:—
“ Calyx monophyllus 4_5-fidus, externè sæpiùs villosus. Tubus expansus subplanus, hemisphæricus, urceolatus, campanulatus vel subcylindricus, liber, vel inferiùs ovario adnatus, vel cum eo omninò cohærens; interiùs nudus, vel in pluribus disco carnoso aut fauci limitato, aut in laciniis effuso, tectus. Lacinia ovatæ, triangulares, rariùs subulatæ, acutæ, interiùs subcarnosæ, in pluribus in media lineâ carnosâ prominente notatæ, et apice callosæ; in præfloratione valvatìm applicatæ.
“ Petala cum calycis laciniis alternantia, ejusque fauci inserta, sæpiùs sub margine disci affixa, unguiculata, ungue plus minùsve longo. Laminæ rariùs patentes, planæ, superiùs integræ vel emarginatæ, in plerisque concavæ, convolutæ vel cucullatæ, stamina vel eorum filamenta involventes, in pluribus nullæ. Præfloratio complicata.
“ Stamina petalis opposita. Filamenta calycis fauci vel margini disci inserta, et cum unguibus petalorum basi sæpiùs cohærentia, laciniis calycis breviora. Antheræ in petalis cucullatis reconditæ, vel è petalis convolutis exsertæ, parte mediâ vel inferiori dorsi ad apicem filamenti affixæ, versatiles, introrsæ (rarissimè extrorsæ); vel ovatæ, biloculares, loculis parallelis, aut basi divergentibus, rimâ longitudinali dehiscentibus; vel reniformes, uniloculares (loculis superiùs confluentibus), rimâ simplici arcuatâ bivalvìm hiantes. Pollen siccum ellipticum, sulco secundum longitudinem notatum; madefactum sphæricum, læve, vel trimamillosum.
“ Discus formâ maxime varians, in Colletiâ parvus, fundumque tubi calycis occupans; in plerisque tubum calycis strato plus minùsve crasso tegens ejusque formam accipiens (in Zizypho, Paliuro, Ventilagine, Hoveniâ, Colubrinâ, subplanus, pentagonus, angulis ad insertionem staminum emarginatis; in Rhamno, Sageretiâ, Scutiâ, urceolatus vel cupulæformis), et fauci margine distincto limitatus; in aliis (Retanillâ, Cryptandrâ, Phylicâ, à plerisque auctoribus ut disco destitutis descriptis) super lacinias calycis etiam effusus, ejusque superficiem interiorem à fundo usque ad apicem laciniarum substantiâ carnosâ incrustans; an in quibusdam nullus ? (in Pomaderri et Cryptandræ speciebus ;) margine petalis staminibusque insertionem præbens.
“Ovarium liberum, disco plus minusve immersum, vel calycis tubo semi-adhærens, seu omninò adhærens; ovatum vel subglobosum, bi-triloculare, rarissimè quadriloculare (in quibusdam Rhamnis); loculis monospermis.
« Ovulum in quolibet loculo solitarium erectum è fundo loculi natum, sessile vel podospermio brevi suffultum. Podospermium, dùm adest, ante evolutionem floris angustum, nec foramen testæ tegens, ad anthesin superiùs dilatatum, et ut cupula parva basin ovuli foramenque amplectens, cellulosospongiosum, vasibus raphes percursum. Testa lævis vel dorso (in Rhamnis) sulco profundo notata, inferiùs prope hilum perforata. Foramen in ovulis sessilibus mammillæ albidæ endocarpii respondens, in pedicellatis cupulâ spongiosâ podospermi tectum, nec ei adhærens. Membrana testæ è stratis tribus formata, exterius cuticulatum tenuissimum, medium transversè fibrosum, testam seminis producturum, interius spongiosum, primùm maximam partem ovuli occupans, dehinc incremento nuclei evanescens, raphes vasa continens. Membrana interior albida, tenuis, primùm libera, deindè testæ plus minusve adhærens (in Pomaderri semi-adnata, in Phylicis, Rhamnis aliisque pluribus omninò adnata), circum chalazam superiùs affixa, inferiùs tubulosa, perforata, tubulo in foramine testæ incluso. Chalaza superiùs notata, è duplici strato (ut in omnibus seminibus) formata; exteriùs vasculosa, vasorum raphes expansione producta, testæ inserta; interiùs spongiosa, in ovulo semi-evoluto fuscescens, nuclei membranâ continua. Nucleus subcylindricus, liber, superiùs chalaze affixus, pendulus, inferiùs in mammillâ brevi, foramine inclusa, productus; interiùs laxè cellulosus, in medio sacculum amnii continens, è mammillâ usque ad chalazam extensum, in cujus