CHAPTER XVIII.
CLASSIFICATION OF DICOTYLEDONS.
Division I.—Choripetalæ.
Nearly all of the dicotyledons may be placed in one of two great divisions distinguished by the character of the petals. In the first group, called Choripetalæ, the petals are separate, or in some degenerate forms entirely absent. As familiar examples of this group, we may select the buttercup, rose, pink, and many others.
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 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.
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.