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her part in the process, and being known as the "suspensor." Later the embryo becomes indented above and forms two lobes (_Q_), which are the beginnings of the cotyledons. The first root and the stem arise from the cells next the suspensor. CHAPTER XVIII. CLASSIFICATION OF DICOTYLEDONS. DIVISION I.--_Choripetalae_. 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 _Choripetalae_, 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. The second group (_Sympetalae_ or _Gamopetalae_) 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 _Sympetalae_, which includes the highest of all plants. [Illustration: FIG. 96.--Iuliflorae. _A_, male; _B_, female inflorescence of a willow, _Salix_ (_Amentaceae_), x 1/2. _C_, a single male flower, x 2. _D_, a female flower, x 2. _E_, cross-section of the ovary, x 8. _F_, an opening fruit. _G_, single seed with its hairy appendage, x 2.] The _Choripetalae_ may be divided into six groups, including twenty-two orders. The first group is called _Iuliflorae_, 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 gynoecium or andraecium, 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 _Iuliflorae_. _A_, branch of hazel, _Corylus_ (_Cupuliferae_), x 1. [Male], male; [Female], female inflorescence. _B_, a single male flower, x 3. _C_, section of the ovary of a female flower, x 25. _D_, acorn of red oak, _Quercus_ (_Cupuliferae_), x 1/2. _E_, seed of white birch, _Betula_ (_Betulaceae_), x 3. _F_, fruit of horn-bean, _Carpinus_ (_Cupuliferae_), x 1. G, lizard-tail, _Saururus_ (_Saurureae_), x 1/4. _H_, a single flower, x 2. _I_, femal
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