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(Arum family), a large and wide-spread botanical order of Monocotyledons containing about 1000 species in 105 genera. It is generally distributed in temperate and tropical regions, but especially developed in warm countries. The common British representative of the order, Arum maculatum Fig.2. Arum maculatum, Cuckoo-pint. About 3 scale of nature.

1. Leaves and inflorescence. succession (from below) female 2. Underground root-stock. flowers, male flowers, and sterile 3. Lower part of spathe cut open. flowers forming a ring of hairs 4. Spike of fruits. Showing in borne on the spadix. (cuckoo-pint, lords and ladies, or wake robin), gives a meagre idea of its development. The plants are generally herbaceous, often, however, reaching a gigantic size, but are sometimes shrubby, as in Pothos, a genus of shrubby climbing plants, chiefly Malayan. Monstera is a tropical American genus of climbing shrubs, with large often much-perforated leaves; the fruiting spikes of a Mexican species, M. deliciosa, are eaten. The roots of the climbing species are of interest in their adaptation to the mode of life of the plant. For instance, some species of Philodendron have a growth like that of ivy, with feeding roots penetrating the soil and clasping roots which fix the plant to its support. In other species of the genus the seed germinates on a branch, and the seedling produces clasping roots, and roots which grow downwards hanging like stout cords, and ultimately reaching the ground. The leaves, which show great variety in size and form, are generally broad and net-veined, but in sweet-flag (Acorus Calamus) are long and narrow with parallel veins. In Arum the blade is simple, as also in the so-called arum-lily (Richardia), a South African species common in Britain as a greenhouse plant, and in Caladium, a tropical South American genus, and Alocasia (tropical Asia), species of which are favourite warm-greenhouse plants on account of their variegated leaves. In other genera the leaves are much divided and sometimes very large; those of Dracontium (tropical America) may be 15 ft. high, with a long stem-like stalk and a much-branched spreading blade. The East Indian genus Amorphophallus has a similar habit. A good series of tropical aroids is to be seen in the aroid house at Kew. The so-called water cabbage (Pistia Stratiotes) is a floating plant widely distributed in the tropics, and consisting of rosettes of broadish leaves several inches across and a tuft of roots hanging in the water.

The small flowers are densely crowded on thick fleshy spikes, which are associated with, and often more or less enveloped by, a large leaf (bract), the so-called spathe, which, as in cuckoo-pint, where it is green in colour, Richardia, where it is white, creamy or yellow, Anthurium, where it is a brilliant scarlet, is often the most striking feature of the plant. The details of the structure of the flower show a wide variation; the flowers are often extremely simple, sometimes as in Arum, reduced to a single stamen or pistil. The fruit is a berry - the scarlet berries of the cuckoo-pint are familiar objects in the hedges in late summer. The plants generally contain an acrid poisonous juice. The underground stems (rhizomes or tubers) are rich in starch; from that of Arum maculatum Portland arrowroot was formerly extensively prepared by pounding with water and then straining; the starch was deposited from the strained liquid.

The order is represented in Britain by Arum maculatum, a low herbaceous plant common in woods and hedgerows in England, but probably not wild in Scotland. It grows from a whitish root-stock which sends up in the spring a few long-stalked, arrow-shaped leaves of a polished green, often marked with dark blotches. These are followed by the inflorescence, a fleshy spadix bearing in the lower part numerous closely crowded simple unisexual flowers and continued above into a purplish or yellowish appendage; the spadix is enveloped by a leafy spathe, constricted in the lower part to form a chamber, in which are the flowers. The mouth of this chamber is protected by a ring of hairs pointing downwards, which allow the entrance but prevent the escape of small flies; after fertilization of the pistils the hairs wither. The insects visit the plant in large numbers, attracted by the foetid smell, and act as carriers of the pollen from one spathe to another. As the fruit ripens the spathe withers, and the brilliant red berries are exposed.

The sweet-flag Acorus Calamus, which occurs apparently wild in England in ditches, ponds, &c., is supposed to have been introduced.