AROIDEAE (Arum

See also:

• FAMILY

family)  , a large and wide-spread botanical order of Monocotyledons containing about moo 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 . 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 (Acorns 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 it. 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 Acorns Calamus (q.v.), which occurs apparently wild in England in ditches, ponds, &c., is supposed to have been introduced .