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.