mily (_Cabombeae_) is also represented at the north by but
one species, the water shield (_Brasenia_), not uncommon in marshes.
Its flowers are quite small, of a dull-purple color, and the leaves
oval in outline and centrally peltate, _i.e._ the leaf stalk inserted
in the centre. The whole plant is covered with a transparent
gelatinous coat.

The third family (_Nymphaeaceae_) includes the common white water-lilies
(_Castalia_) and the yellow water-lilies (_Nymphaea_) (Fig. 102, _A_).
In the latter the petals are small and inconspicuous (Fig. 102, _C_,
_p_), but the sepals are large and showy. In this family the carpels,
instead of being separate, are united into a large compound pistil.
The water-lilies reach their greatest perfection in the tropics, where
they attain an enormous size, the white, blue, or red flowers of some
species being thirty centimetres or more in diameter, and the leaves
of the great _Victoria regia_ of the Amazon reaching two metres or
more in width.

The third order of the _Aphanocyclae_ (_Rhoeadinae_ or _Cruciflorae_)
comprises a number of common plants, principally characterized by
having the parts of the flowers in twos or fours, so that they are
more or less distinctly cross-shaped, whence the name _Cruciflorae_.

There are four families, of which the first is the poppy family
(_Papaveraceae_), including the poppies, eschscholtzias, Mexican or
prickly poppy (_Argemone_), etc., of the gardens, and the blood-root
(_Sanguinaria_), celandine poppy (_Stylophorum_), and a few other wild
plants (see Fig. 103, _A-I_). Most of the family have a colored juice
(latex), which is white in the poppy, yellow in celandine and
_Argemone_, and orange-red in the blood-root. From the latex of the
opium poppy the opium of commerce is extracted.

[Illustration: FIG. 103.--Types of _Aphanocyclae_ (_Rhoedinae_). _A_,
plant of blood-root, _Sanguinaria_ (_Papaveraceae_), x 1/3. _B_, a single
flower, x 1. _C_, fruit, x 1/2. _D_, section of the seed. _em._ embryo,
x 2. _E_, diagram of the flower. _F_, flower of Dutchman's breeches,
_Dicentra_ (_Fumariaceae_), x 1. _G_, group of three stamens of the
same, x 2. _H_, one of the inner petals, x 2. _I_, fruit of celandine
poppy, _Stylophorum_ (_Papaveraceae_), x 1/2. _J_, flower of mustard,
_Brassica_ (_Cruciferae_), x 1. _K_, the same, with the petals removed,
x 2. _L_, fruit of the same, x 1.]

The second family, the fumitories (_Fumariaceae_) are delicate, smooth
pl