There are three orders of the _Iulifloræ_: _Amentaceæ_, _Piperineæ_, and _Urticinæ_. The first contains the birches (_Betulaceæ_); oaks, beeches, hazels, etc. (_Cupuliferæ_); walnuts and hickories (_Juglandeæ_); willows and poplars (_Salicaceæ_). They are all trees or shrubs; the fruit is often a nut, and the embryo is very large, completely filling it. The _Piperineæ_ 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 _Urticinæ_ include, among our common plants, the nettle family (_Urticaceæ_); plane family (_Plataneæ_), represented by the sycamore or buttonwood (_Platanus_); the hemp family (_Cannabineæ_); and the elm family (_Ulmaceæ_). 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 _Choripetalæ_ is called _Centrospermæ_, and includes but a single order comprising seven families, all of which, except one (_Nyctagineæ_), are represented by numerous native species. The latter comprises mostly tropical plants, and is represented in our gardens by the showy "four-o'clock" (_Mirabilis_). In this plant, as in most of the order, the corolla is absent, but here the calyx is large and brightly colored, resembling closely the corolla of a morning-glory or petunia. The stamens are usually more numerous than the sepals, and the pistil, though composed of several carpels, has, as a rule, but a single cavity with the ovules arising from the base, though sometimes the ovary is several celled. [Illustration: FIG. 98.--Types of _Centrospermæ_. _A_, plant of spring-beauty, _Claytonia_ (_Portulacaceæ_), × ½. _B_, a single flower, × 1. _C_, fruit, with the sepals removed, × 2. _D_, section of the seed, showing the curved embryo (_em._), × 5. _E_, single flower of smart-weed, _Polygonum_ (_Polygonaceæ_), × 2. _F_, the pistil, × 2. _G_, section of the ovary, showing the single ovule, × 4. _H_, section of the seed, × 2. _I_, base of the leaf, showing the sheath, × 1. _J_, flower of pig-weed, _Chenopodium_ (_Chenopodiaceæ_), × 3: i, from without; ii, in section. _K_, flower of the poke-weed, _Phytolacca_ (_Phytolaccaceæ_), × 2. _L_, fire-pink, _Silene_ (_Caryophyllaceæ_), × ½. _M_, a flower with half of the calyx and corolla removed, × 1. _N_, ripe fruit of mouse-ear chick-weed, _Cerastium_ (_Caryophyllaceæ_), opening by ten teeth at the summit, × 2. _O_, diagram of the flower of _Silene_.]