The second group (_Sympetalæ_ or _Gamopetalæ_) comprises those dicotyledons whose flowers have the petals more or less completely united into a tube. The honeysuckles, mints, huckleberry, lilac, etc., are familiar representatives of the _Sympetalæ_, which includes the highest of all plants. [Illustration: FIG. 96.--Iulifloræ. _A_, male; _B_, female inflorescence of a willow, _Salix_ (_Amentaceæ_), × ½. _C_, a single male flower, × 2. _D_, a female flower, × 2. _E_, cross-section of the ovary, × 8. _F_, an opening fruit. _G_, single seed with its hairy appendage, × 2.] The _Choripetalæ_ may be divided into six groups, including twenty-two orders. The first group is called _Iulifloræ_, and contains numerous, familiar plants, mostly trees. In these plants, the flowers are small and inconspicuous, and usually crowded into dense catkins, as in willows (Fig. 96) and poplars, or in spikes or heads, as in the lizard-tail (Fig. 97, _G_), or hop (Fig. 97, _I_). The individual flowers are very small and simple in structure, being often reduced to the gynœcium or andræcium, carpels and stamens being almost always in separate flowers. The outer leaves of the flower (sepals and petals) are either entirely wanting or much reduced, and never differentiated into calyx and corolla. [Illustration: FIG. 97.--Types of _Iulifloræ_. _A_, branch of hazel, _Corylus_ (_Cupuliferæ_), × 1. ♂, male; ♀, female inflorescence. _B_, a single male flower, × 3. _C_, section of the ovary of a female flower, × 25. _D_, acorn of red oak, _Quercus_ (_Cupuliferæ_), × ½. _E_, seed of white birch, _Betula_ (_Betulaceæ_), × 3. _F_, fruit of horn-bean, _Carpinus_ (_Cupuliferæ_), × 1. G, lizard-tail, _Saururus_ (_Saurureæ_), × ¼. _H_, a single flower, × 2. _I_, female inflorescence of the hop, _Humulus_ (_Cannabineæ_), × 1. _J_, a single scale with two flowers, × 1. _K_, a male flower of a nettle, _Urtica_ (_Urticaceæ_), × 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.