lantarum
secundum Ordines Naturales disposita_ (1789) is the first which can
claim to be a natural system. The orders are carefully characterized,
and those of Angiosperms are grouped in fourteen classes under the two
main divisions Monocotyledons and Dicotyledons. The former comprise
three classes, which are distinguished by the relative position of the
stamens and ovary; the eleven classes of the latter are based on the
same set of characters and fall into the larger subdivisions Apetalae,
Monopetalae and Polypetalae, characterized respectively by absence,
union or freedom of the petals, and a subdivision, _Diclines
Irregulares_, a very unnatural group, including one class only. A.P.
de Candolle introduced several improvements into the system. In his
arrangement the last subdivision disappears, and the Dicotyledons fall
into two groups, a larger containing those in which both calyx and
corolla are present in the flower, and a smaller, Monochlamydeae,
representing the Apetalae and _Diclines Irregulares_ of Jussieu.
The dichlamydeous group is subdivided into three, Thalamiflorae,
Calyciflorae and Corolliflorae, depending on the position and union of
the petals. This, which we may distinguish as the French system,
finds its most perfect expression in the classic _Genera Plantarum_
(1862-1883) of Bentham and Hooker, a work containing a description,
based on careful examination of specimens, of all known genera of
flowering plants. The subdivision is as follows:--

DICOTYLEDONS.

Polypetalae:
Thalamiflorae.
Disciflorae.
Calyciflorae.

Gamopetalae:
Inferae.
Heteromerae.
Bicarpellatae.

Monochlamydeae in eight series.
Monocotyledons in seven series.

Of the Polypetalae, series 1, Thalamiflorae, is characterized by
hypogynous petals and stamens, and contains 34 orders distributed in 6
larger groups or cohorts. Series 2, Disciflorae, takes its name from
a development of the floral axis which forms a ring or cushion at the
base of the ovary or is broken up into glands; the ovary is superior.
It contains 23 orders in 4 cohorts. Series 3, Calyciflorae, has petals
and stamens perigynous, or sometimes superior. It contains 27 orders
in 5 cohorts.

Of the Gamopetalae, series 1, Inferae, has an interior ovary and
stamens usually as many as the corolla-lobes. It contains 9 orders
in 3 cohorts. Series 2, Heteromerae, has generally a superior ovary,
stamens as many as the corolla-lobes or more, and mo