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