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.
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.
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.