e inflorescence of the hop, _Humulus_ (_Cannabineae_), x 1.
_J_, a single scale with two flowers, x 1. _K_, a male flower of a
nettle, _Urtica_ (_Urticaceae_), x 5.]

In the willows (Fig. 96) the stamens are bright-colored, so that the
flowers are quite showy, and attract numerous insects which visit them
for pollen and nectar, and serve to carry the pollen to the pistillate
flowers, thus insuring their fertilization. In the majority of the
group, however, the flowers are wind-fertilized. An excellent example
of this is seen in the common hazel (Fig. 97, _A_). The male flowers
are produced in great numbers in drooping catkins at the ends of the
branches, shedding the pollen in early spring before the leaves
unfold. The female flowers are produced on the same branches, but
lower down, and in much smaller numbers. The stigmas are long, and
covered with minute hairs that catch the pollen which is shaken out
in clouds every time the plant is shaken by the wind, and falls in a
shower over the stigmas. A similar arrangement is seen in the oaks,
hickories, and walnuts.

There are three orders of the _Iuliflorae_: _Amentaceae_, _Piperineae_,
and _Urticinae_. The first contains the birches (_Betulaceae_); oaks,
beeches, hazels, etc. (_Cupuliferae_); walnuts and hickories
(_Juglandeae_); willows and poplars (_Salicaceae_). They are all trees
or shrubs; the fruit is often a nut, and the embryo is very large,
completely filling it.

The _Piperineae_ are mostly tropical plants, and include the pepper
plant (_Piper_), as well as other plants with similar properties. Of
our native forms, the only common one is the lizard-tail (_Saururus_),
not uncommon in swampy ground. In these plants, the calyx and corolla
are entirely absent, but the flowers have both carpels and stamens
(Fig. 97, _H_).

The _Urticinae_ include, among our common plants, the nettle family
(_Urticaceae_); plane family (_Plataneae_), represented by the sycamore
or buttonwood (_Platanus_); the hemp family (_Cannabineae_); and the
elm family (_Ulmaceae_). The flowers usually have a calyx, and may
have only stamens or carpels, or both. Sometimes the part of the stem
bearing the flowers may become enlarged and juicy, forming a
fruit-like structure. Well-known examples of this are the fig and
mulberry.

The second group of the _Choripetalae_ is called _Centrospermae_, and
includes but a single order comprising seven families, all of which,
except one (_Nyctagineae_)