ith part of the calyx and corolla removed, x 2. _C_,
fruit of white ash, _Fraxinus_ (_Oleaceae_), x 1. _D_, flower of
pink-root, _Spigelia_ (_Loganiaceae_), x 1/2. _E_, cross-section of the
ovary, x 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceae_),
x 1/2. _G_, diagram of the flower. _H_, flowering branch of dog-bane,
_Apocynum_ (_Apocynaceae_), x 1/2. _I_, vertical section of a flower,
x 2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadaceae_),
x 1. _L_, vertical section through the upper part of the flower, x 2.
_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen
masses, x 6. _N_, a nearly ripe seed, x 1.]

The last family is the milk-weeds (_Asclepiadaceae_), which have
extremely complicated flowers. Our numerous milk-weeds (Fig. 122, _K_)
are familiar representatives, and exhibit perfectly the peculiarities
of the family. Like the dog-banes, the plants contain a milky juice
which is often poisonous. Besides the true milk-weeds (_Asclepias_),
there are several other genera within the United States, but mostly
southern in their distribution. Many of them are twining plants and
occasionally cultivated for their showy flowers. Of the cultivated
forms, the wax-plant (_Hoya_), and _Physianthus_ are the commonest.

[Illustration: FIG. 123.--_Anisocarpous sympetalae_ (_Campanulinae_).
_A_, vertical section of the bud of American bell-flower, _Campanula_
(_Campanulaceae_), x 2. _B_, an expanded flower, x 1. The stamens have
discharged their pollen, and the stigma has opened. _C_, cross-section
of the ovary, x 3. _D_, flower of the Carpathian bell-flower
(_Campanula Carpatica_), x 1. _E_, flower of cardinal-flower,
_Lobelia_ (_Lobeliaceae_), x 1. _F_, the same, with the corolla and
sepals removed. _an._ the united anthers. _gy._ the tip of the pistil.
_G_, the tip of the pistil, x 2, showing the circle of hairs
surrounding the stigma. _H_, cross-section of the ovary, x 3. _I_, tip
of a branch of cucumber, _Cucurbita_ (_Cucurbitaceae_), with an
expanded female flower ([Female]). _J_, androecium of a male flower,
showing the peculiar convoluted anthers (_an._), x 2. _K_,
cross-section of the ovary, x 2.]

The fourth order (_Campanulinae_) also embraces five families, but of
these only three are represented among our wild plants. The
bell-flowers (_Campanula_) (Fig. 123, _A_, _D_) are examples of the
family _Campanulaceae_, and numerous species are common, both wild and
cultivated.