-_Eucyclae_ (_Terebinthinae_, _AEsculinae_). _A_,
leaves and flowers of sugar-maple, _Acer_ (_Aceraceae_), x 1/2. _B_, a
male flower, x 2. _C_, diagram of a perfect flower. _D_, fruit of the
silver-maple, x 1/2. _E_, section across the seed, x 2. _F_, embryo
removed from the seed, x 1. _G_, leaves and flowers of bladder-nut,
_Staphylea_, (_Sapindaceae_), x 1/2. _H_, section of a flower, x 2. _I_,
diagram of the flower. _J_, flower of buckeye (_AEsculus_), x 11/2. _K_,
flower of smoke-tree, _Rhus_ (_Anacardiaceae_), x 3. _L_, the same, in
section.]

The second order (_Terebinthinae_) contains but few common plants.
There are six families, mostly inhabitants of the warmer parts of
the world. The best-known members of the order are the orange, lemon,
citron, and their allies. Of our native plants the prickly ash
(_Zanthoxylum_), and the various species of sumach (_Rhus_), are
the best known. In the latter genus belong the poison ivy
(_R. toxicodendron_) and the poison dogwood (_R. venenata_). The
Venetian sumach or smoke-tree (_R. Cotinus_) is commonly planted for
ornament.

The third order of the _Eucyclae_, the _AEsculinae_, embraces six
families, of which three, the horsechestnuts, etc. (_Sapindaceae_), the
maples (_Aceraceae_), and the milkworts (_Polygalaceae_), have several
representatives in the northern United States. Of the first the
buckeye (_AEsculus_) (Fig. 108, _J_) and the bladder-nut (_Staphylea_)
(Fig. 108, _G_) are the commonest native genera, while the
horsechestnut (_AEsculus hippocastanum_) is everywhere planted.

The various species of maple (_Acer_) are familiar examples of the
_Aceraceae_ (see Fig. 106, _A_, _F_).

The fourth and last order of the _Eucyclae_, the _Frangulinae_, is
composed mainly of plants with inconspicuous flowers, the stamens as
many as the petals. Not infrequently they are dioecious, or in some,
like the grape, some of the flowers may be unisexual while others are
hermaphrodite (_i.e._ have both stamens and pistil). Among the
commoner plants of the order may be mentioned the spindle-tree, or
burning-bush, as it is sometimes called (_Euonymus_) (Fig. 109, _A_),
and the climbing bitter-sweet (_Celastrus_) (Fig. 109, _D_), belonging
to the family _Celastraceae_; the holly and black alder, species of
_Ilex_, are examples of the family _Aquifoliaceae_; the various species
of grape (_Vitis_), the Virginia creeper (_Ampelopsis quinquefolia_),
and one or two other cultivated species