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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
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