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, 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 _Centrospermae_. _A_, plant of spring-beauty, _Claytonia_ (_Portulacaceae_), x 1/2. _B_, a single flower, x 1. _C_, fruit, with the sepals removed, x 2. _D_, section of the seed, showing the curved embryo (_em._), x 5. _E_, single flower of smart-weed, _Polygonum_ (_Polygonaceae_), x 2. _F_, the pistil, x 2. _G_, section of the ovary, showing the single ovule, x 4. _H_, section of the seed, x 2. _I_, base of the leaf, showing the sheath, x 1. _J_, flower of pig-weed, _Chenopodium_ (_Chenopodiaceae_), x 3: i, from without; ii, in section. _K_, flower of the poke-weed, _Phytolacca_ (_Phytolaccaceae_), x 2. _L_, fire-pink, _Silene_ (_Caryophyllaceae_), x 1/2. _M_, a flower with half of the calyx and corolla removed, x 1. _N_, ripe fruit of mouse-ear chick-weed, _Cerastium_ (_Caryophyllaceae_), opening by ten teeth at the summit, x 2. _O_, diagram of the flower of _Silene_.] The first family (_Polygoneae_) is represented by the various species of _Polygonum_ (knotgrass, smart-weed, etc.), and among cultivated plants by the buckwheat (_Fagopyrum_). The goose-foot or pig-weed (_Chenopodium_) among native plants, and the beet and spinach of the gardens are examples of the family _Chenopodiaceae_. Nearly resembling the last is the amaranth family (_Amarantaceae_), of which the showy amaranths and coxcombs of the gardens, and the coarse, green amaranth or pig-weed are representatives. The poke-weed (_Phytolacca_) (Fig. 98, _K_), so conspicuous in autumn on account of its dark-purple clusters of berries and crimson stalks, is our only representative of the family _Phytolaccaceae_. The two highest families are the purslane family (_Portulacaceae_) and pink family (_Caryophylleae_). These are mostly plants with showy flowers in which the petals are large and conspicuous, though some of the pink family, _e.g._ some chick-weeds, have
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