IRRITABILITY 943 IRVING

IRRITABILITY

943

IRVING

In the arid regions there are yet millions of acres that lack only water to make them productive, already possessing, as they do, the other elements of fruittulness. In the United States prior to 1870 probably less than 20,000 acres were irrigated; by 1880 the area was probably 50 times greater; and the 12th census showed that in 1899 there were 7,539,545 acres irrigated, representing 108,218 farms, producing crops valued at nearly $87,000,000, of which more than $84,000,000 was credited to the irrigated fields of the 11 arid states and territories of Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming.

The various governmental projects for storing the flood-waters instituted since then, together with the numerous private enterprises, including the improvement, enlargement and extension of canals and better administration of the water supply, promise to make productive wide areas heretofore barren.                 F. D. Coburn.

Ir'ritabil'ity (inplants). A state or condition of protoplasm in which it undergoes a change in consequence of a change in the neighboring protoplasm or in its surroundings. The change in the surroundings is called a stimulus; the change produced in the protoplasm is called a response or reaction. In plants the reaction follows the stimulus after a perceptible time, seconds (rarely less), minutes or even hours; whereas in most animals the interval (reaction time) is much less. So slow are some plant reactions that the stimulus may cease to act long before any reaction appears. Such late reactions are known as after-effects The energy of the reaction is often many times that of the stimulus; so, although the sequence is that of cause and effect, the stimulus merely starts the action of protoplasm, which itself is the source of the energy expended in whatever work is done. Since the protoplasm ceases to react after more or less prolonged stimulation, it is supposed that it forms some material which, decomposing under stimulation, becomes exhausted when the stimulus is frequently applied and is only formed again during a period of rest. There are many kinds of stimuli : contact, friction, stress, gravity, light, heat, electricity and chemical substances, including water and air. Only certain parts are sensitive to particular stimuli. The action of the more important stimuli is described under Chemotaxis, Chemotropism, Geotropism, Heliotro-pism, Hydropism, Phototaxis, Rheotro-pism and Thermotropism. Through the chemical stimuli, probably, one part of the protoplasm influences another. Thus the change in one region, caused by some external stimulus, may act as a stimulus on neighboring protoplasm. These reactions, however, may be unseen, and a visible

change may occur only at a distance from the point where the external stimulus acted. Thus, if a leaflet of the sensitive plant be scorched, all the leaflets of that leaf or even all the leaves on the plant may change their position. In such an event the stimulus is said to be transmitted from the region where it is first applied to the region where a visible response occurs. Nothing is satisfactorily known as to the processes in such transmission. Each kind of sensitiveness exists only under conditions favorable to it; prolonged unfavorable conditions produce disease, more or less severe; if conditions unfavorable to general irritability continue too long, death ensues. Indeed Sachs says: "Life is inconceivable without irritability; the dead organism is dead simply because it has lost its irritability." Irtish (ïr'tïsh), a river of Siberia, the chief branch of the Obi. It rises at the east end of the Altai Mountains, flows toward the northwest for a total distance of 1,620 miles and joins the Obi at Samarow. From April to November it is navigable to Lake Saison.

Irving (er'vïng), Sir Henry, a noted Eng-glish actor, was born at Keinton, England,

in 1838. H i s family name was Brodribb, but by royal license he was permitted to assume the name of Irving. He was educated at London. From an early age he displayed a strong love for the stage, and made his first appearance a t Sunderland theater in 1856. In spite of tricks of voice, gait and gesture, he was at the head of English actors of the time, and did much to elevate the drama. He visited the" United States several times, and was always received with great enthusiasm. His chief rôles were well known to theatre-goers, especially his Charles I, Hamlet, Macbeth, Richard III and Matthias in The Bells. He was knighted in 1895. He died on Oct. 13, 1905.

Irving, Washington, one of the best-known of American writers, was born at New York, April 3, 1783. He entered a law office at 16, his health preventing his taking a college course. His father's large library had supplied him with reading, Chaucer and Spenser being his favorite authors. In 1804 he traveled in Europe, meeting Allston, Kemble and Mrs. Siddons. He began writing in 1807, by essays contributed to a periodical called Salmagundi. His first large

SIR HENRY IRVING