ants. The smallest members of
the group are little aquatics, scarcely visible to the naked eye, and
of extremely simple structure, but nevertheless these little plants
produce true flowers. In marked contrast to these are the palms, some
of which reach a height of thirty metres or more.

The flowers in most of the order are small and inconspicuous, but
aggregated on a spike (spadix) which may be of very large size. Good
types of the order are the various aroids (_Aroideae_), of which the
calla (_Richardia_) is a very familiar cultivated example. Of wild
forms the sweet-flag (_Acorus_), Jack-in-the-pulpit (_Arisaema_)
(Fig. 86, _A_, _D_), skunk-cabbage (_Symplocarpus_), and wild calla
may be noted. In _Arisaema_ (Fig. 86, _A_) the flowers are borne only
on the base of the spadix, and the plant is dioecious. The flowers are
of the simplest structure, the female consisting of a single carpel,
and the male of four stamens (_C_, _D_). While the individual flowers
are destitute of a perigone, the whole inflorescence (cluster of
flowers) is surrounded by a large leaf (spathe), which sometimes is
brilliantly colored, this serving to attract insects. The leaves of
the aroids are generally large and sometimes compound, the only
instance of true compound leaves among the monocotyledons (Fig. 86,
_B_).

[Illustration: FIG. 86.--Types of _Spadiciflorae_. _A_, inflorescence
of Jack-in-the-pulpit (_Arisaema_, _Aroideae_). The flowers (_fl._) are
at the base of a spike (spadix), surrounded by a sheath (spathe),
which has been cut away on one side in order to show the flowers, x 1/2.
_B_, leaf of the same plant, x 1/4. _C_, vertical section of a female
flower, x 2. _D_, three male flowers, each consisting of four stamens,
x 2. _E_, two plants of a duck-weed (_Lemna_), the one at the left is
in flower, x 4. _F_, another common species. _L_, _Trisulea_, x 1.
_G_, male flower of _E_, x 25. _H_, optical section of the female
flower, showing the single ovule (_ov._), x 25. _I_, part of the
inflorescence of the bur-reed (_Sparganium_), with female flowers, x 1/2
(_Typhaceae_). _J_, a single, female flower, x 2. _K_, a ripe fruit,
x 1. _L_, longitudinal section of the same. _M_, two male flowers,
x 1. _N_, a pond-weed (_Potomogeton_), x 1 (_Naiadaceae_). _O_, a
single flower, x 2. _P_, the same, with the perianth removed, x 2.
_Q_, fruit of the same, x 2.]

Probably to be regarded as reduced aroids are the duck-weeds
(_Lemnaceae_) (Fig. 86