AR´RIA, the heroic wife of a Roman named Cæc[=i]na Pætus. Pætus was condemned to death in A.D. 42 for his share in a conspiracy against the emperor Claudius, and was encouraged to suicide by his wife, who stabbed herself and then handed the dagger to her husband with the words, 'It does not hurt, Pætus!'
AR´RIAN, or FLAVIUS ARRIANUS, a Greek historian, native of Nicomedia, flourished in the second century, under the emperor Hadrian and the Antonines. He was first a priest of Ceres; but at Rome he became a disciple of Epictetus, was honoured with the citizenship of Rome, and was advanced to the senatorial and even consular dignities. His extant works are: _The Expedition of Alexander_, in seven books; a book _On the Affairs of India_; an _Epistle to Hadrian_; a _Treatise on Tactics_; a _Periplus of the Euxine Sea_; a _Periplus of the Red Sea_; and his _Enchiridion_, a moral treatise, containing the discourses of Epictetus.
AR´RIS, in architecture, the line in which the two straight or curved surfaces of a body, forming an exterior angle, meet each other.
ARRO´BA (Spanish), a weight formerly used in Spain, and still used in the greater part of Central and South America. In the States of Spanish origin its weight is generally equal to 25.35 lb. avoirdupois; in Brazil it equals 32.38 lb.--Also a measure for wine, spirits, and oil, ranging from 2¾ gallons to about 10 gallons.
ARROWHEAD (Sagittaria), a genus of aquatic plants found in all parts of the world within the torrid and temperate zones, nat. ord. Alismaceæ, distinguished by possessing barren and fertile flowers, with a three-leaved calyx and three coloured petals. The common arrowhead (_S. sagittifolia_), the only native species in Britain, is known by its arrow-shaped leaves with lanceolate straight lobes.
ARROWHEADED CHARACTERS. See _Cuneiform Writing_.
ARROW LAKE, an expansion of the Columbia River, in British Columbia, Canada; about 95 miles long from N. to S.; often regarded as forming two lakes--Upper and Lower Arrow Lake.
ARROWROCK DAM. See _Dams_ and _Reservoirs_.
[Illustration: Arrow-root (_Maranta arundin[=a]c[)e]a_)]
ARROW-ROOT, a starch largely used for food and for other purposes. Arrow-root proper is obtained from the rhizomes or rootstocks of several species of plants of the genus Maranta (nat. ord. Marantaceæ), and perhaps owes its name to the scales which cover the rhizome, which have some resemblance to the point of an arrow. Some, however, suppose that the name is due to the fact of the fresh roots being used as an application against wounds inflicted by poisoned arrows, and others say that _arrow_ is a corruption of _ara_, the Indian name of the plant. The species from which arrow-root is most commonly obtained is _M. arundin[=a]c[)e]a_, hence called the _arrow-root plant_. Brazilian arrow-root, or tapioca meal, is got from the large fleshy root of _Manihot utilissima_, after the poisonous juice has been got rid of; East Indian arrow-root, from the large rootstocks of _Curc[)u]ma angustifolia_; Chinese arrow-root, from the creeping rhizomes of _Nelumbium speci[=o]sum_; English arrow-root, from the potato; Portland arrow-root, from the corms of _Arum macul[=a]tum_; and Oswego arrow-root, from Indian corn. Analyses made in 1902 and 1906 show that the idea generally held of the nourishing qualities of arrow-root is a delusion, and that the proteids, which are true muscle-builders, are present in an extremely small extent. Arrow-root, however, mixed with eggs, milk, and flavourings, is largely used in the dietary of invalids.