§ 3 System
547. Two systems of classification used to be recognized in botany,—the artificial and the natural; but only the latter is now thought to deserve the name of a system.
548. Artificial classifications have for object merely the ascertaining of the name and place of a plant. They do not attempt to express relationships, but serve as a kind of dictionary. They distribute the genera and species according to some one peculiarity or set of peculiarities (just as a dictionary distributes words according to their first letters), disregarding all other considerations. At present an artificial classification in botany is needed only as a key to the natural orders,—as an aid in referring an unknown plant to its proper family; and such keys are still very needful, at least for the beginner. Formerly, when the orders themselves were not clearly made out, an artificial classification was required to lead the student down to the genus. Two such classifications were long in vogue: First, that of Tournefort, founded mainly on the leaves of the flower, the calyx and corolla: this was the prevalent system throughout the first half of the eighteenth century; but it has long since gone by. It was succeeded by the well-known
549. Artificial System of Linnæus, which was founded on the stamens and pistils. It consists of twenty-four classes, and of a variable number of orders; the classes founded mainly on the number and disposition of the stamens; the orders partly upon the number of styles or stigmas, partly upon other considerations. Useful and popular as this system was down to a time within the memory of still surviving botanists, it is now completely obsolete. But the tradition of it survives in the names of its classes, Monandria, Diandria, Triandria, etc., which are familiar in terminology in the adjective terms monandrous, diandrous, triandrous, etc. (284); also of the orders, Monogynia, Digynia, Trigynia, etc., preserved in the form of monogynous, digynous, trigynous, etc. (301); and in the name Cryptogamia, that of the 24th class, which is continued for the lower series in the natural classification.
550. Natural System. A genuine system of botany consists of the orders or families, duly arranged under their classes, and having the tribes, the genera, and the species arranged in them according to their relationships. This, when properly carried out, is the Natural System; because it is intended to express, as well as possible, the various degrees of relationship among plants, as presented in nature; that is, to rank those species and those genera, etc., next to each other in the classification which are really most alike in all respects, or, in other words, which are constructed most nearly on the same particular plan.
551. There can be only one natural system of botany, if by this term is meant the plan according to which the vegetable creation was called into being, with all its grades and diversities among the species, as well of past as of the present time. But there may be many natural systems, if we mean the attempts of men to interpret and express that plan,—systems which will vary with advancing knowledge, and with the judgment and skill of different botanists. These must all be very imperfect, bear the impress of individual minds, and be shaped by the current philosophy of the age. But the endeavor always is to make the classification answer to Nature, as far as any system can which has to be expressed in a definite and serial arrangement.
552. So, although the classes, orders, genera, etc., are natural, or as natural as the systematist can make them, their grouping or order of arrangement in a book, must necessarily be in great measure artificial. Indeed, it is quite impossible to arrange the orders, or even the few classes, in a single series, and yet have each group stand next to its nearest relatives on both sides.
553. Especially it should be understood that, although phanerogamous plants are of higher grade than cryptogamous, and angiospermous or ordinary phanerogamous higher than the gymnospermous, yet there is no culmination in the vegetable kingdom, nor any highest or lowest order of phanerogamous plants.
554. The particular system most largely used at present in the classification of the orders is essentially the following:—
Series I. PHANEROGAMIA: Phanerogamous or Flowering Plants. Class I. DICOTYLEDONES ANGIOSPERMEÆ, called for shortness in English, Dicotyledons or Dicotyls. Ovules in a closed ovary. Embryo dicotyledonous. Stem with exogenous plan of growth. Leaves reticulate-veined,
Artificial Division I. Polypetalæ, with petals mostly present and distinct. Orders about 80 in number, Ranunculaceæ to Cornaceæ.
Artificial Division II. Gamopetalæ, with gamopetalous corolla. Orders about 45, Caprifoliaceæ to Plantaginaceæ.
Artificial Division III. Apetalæ or Incompletæ, with perianth, when present, of calyx only. Orders about 35 in number, from Nyctaginaceæ to Salicaceæ. Class II. DICOTYLEDONES GYMNOSPERMEÆ, in English Gymnosperms. No ovary or pericarp, but ovules and seeds naked, and no proper calyx nor corolla. Embryo dicotyledonous or polycotyledonous. Stem with exogenous plan of growth. Leaves mostly parallel-veined. Consists of order Gnetaceæ, which strictly connects with Angiospermous Dicotyls, of Coniferæ, and of Cycadaceæ. Class III. MONOCOTYLEDONES, in English Monocotyledons or Monocotyls. Angiospermous. Embryo monocotyledonous. Stem with endogenous plan of growth. Leaves mostly parallel-veined.
Division I. Petaloideæ. Perianth complete, having the equivalent of both calyx and corolla, and all the inner series corolline. About 18 orders.
Division II. Calycinæ. Perianth complete (in two series) but not corolline, mostly thickish or glumaceous. Chiefly two orders, Juncaceæ, the true Rushes, and Palmæ, Palms.
Division III. Spadicifloræ or Nudifloræ. Perianth none, or rudimentary and incomplete: inflorescence spadiceous. Of five orders, Typhaceæ and Aroideæ the principal.
Division IV. Glumaceæ. Perianth none, or very rudimentary: glumaceous bracts to the flowers. Orders mainly Cyperaceæ and Gramineæ.
Series II. CRYPTOGAMIA: Cryptogamous or Flowerless Plants.
CLASS I. PTERIDOPHYTA, Pteridophytes (484).
CLASS II. BRYOPHYTA, Bryophytes (498).
CLASS III. THALLOPHYTA, Thallophytes (503).