horsehair worm or hairworm or gordian worm Any of about 250-300 species (class Nematomorpha, or Gordiacea; phylum Aschelm- inthes) of long, thin worms. The young are parasites in arthropods; the adults are free-living in the sea or in freshwater. The hairlike body some¬ times grows to a length of about 39 in. (1 m).
horsemanship Art of training, riding, and handling horses. Good horsemanship requires that a rider control the animal’s direction, gait, and speed with maximum effectiveness and minimum effort. Natural aids are a rider’s balance, hands, voice, and legs; artificial aids include bits, reins, saddles, and spurs. Horsemanship was important to cavalrymen and cow¬ boys, and is the fundamental element of dressage.
horsepower Common unit of power, the rate at which work is done. In the English system, one horsepower equals 33,000 foot-pounds of work per minute—that is, the power necessary to lift a total of 33,000 lbs a distance of one foot in one minute. This value was adopted by James Watt in the late 18th century after experiments with strong dray horses and is actually about 50% more than the rate an average horse can sustain for a working day. The electrical equivalent of one horsepower is 746 watts in the International System of Units; the heat equivalent is 2,545 BTU per hour. The metric horsepower (see metric system) equals 4,500 kg-m per minute (32,549 foot-pounds per minute), or 0.9863 horsepower.
horseradish Hardy perennial plant ( Armoracia lapathifolia ) of the mustard family, native to Mediterranean lands and grown throughout the temperate zones. Its hotly pungent, fleshy root is used as a condiment and is traditionally considered medicinal. In many cool, moist areas it has become a troublesome weed. The plant bears small white flowers, small oblong pods, and large, coarse, glossy-green basal leaves arising on long stems from the crown atop the large white root.
pastern
of hip
croup dock tail flank
•gaskin — hock
forearm
knee
coronet
heel
forehead
cheek
muzzle neck jugular groove shoulder breast —
External features of a horse.
© MERRIAM-WEBSTER INC.
horse-chestnut family Family Hippocastanaceae, composed of the buckeyes and the horse chestnuts (genus Aesculus), native to the northern temperate zone. The best-known species of horse chestnut is the com¬ mon, or European, horse chestnut ( A. hippocastanum), native to south¬ eastern Europe but widely cultivated as a large shade and street tree. The Champs-Elysees in Paris is lined with rows of horse-chestnut trees.
horse racing Sport of running horses at speed. Typically, Thorough¬ breds are raced with a rider astride and Standardbreds with the horse pull¬ ing a conveyance with a driver. Though racing has an ancient lineage, the first regularly organized national races were established in England under Charles II (r. 1660-85), and the first in North America were held on Long Island in 1665. These early races were match events between two or three horses and were run in heats; a horse had to complete at least two heats to be judged the winner. By the mid-18th century, larger fields of runners and single-race “dash” events were the norm. Handicap racing emerged in
horseshoe pitching Game for two or four players in which a horse¬ shoe is thrown so as to encircle or land as close as possible to a stake. A horseshoe encircling the stake is called a ringer and counts for the high¬ est score. The game may have derived from quoits, and it became espe¬ cially popular in the U.S. and Canada. Regulation games are played to a winning score of 50, informal games to 21.
horseshoe crab Any of four extant species of marine arthropods (order Xiphosura, subphylum Cheli- cerata), found on the eastern coasts of Asia (three species) and North America (one species). Despite the name, horseshoe crabs are not crabs; they are more closely related to scor¬ pions. Fossil relatives date back 505 million years. They are most abun¬ dant in estuarine waters. The North American species, Limulus polyphe- mus, can grow to more than 2 ft (60 cm) long. The body consists of three parts hinged together: a broad, horseshoe-shaped cephalothorax; a much smaller, segmented abdomen;
and a long, sharp tail-spine, or telson. They spawn on sandy beaches in spring and summer. Adults feed on marine worms; larvae feed on small organisms.
Horseshoe crab (Limulus polyphemus).
RUNK/SCHOENBERGER FROM GRANT HEILMAN
© 2006 Encyclopaedia Britannica, Inc.
898 I horsetail ► hot spot
horsetail also called scouring rush Any of the 30 species of rush- like (see rush), conspicuously segmented, perennial herbaceous plants that make up the genus Equisetum. They grow in moist, rich soils everywhere except Australasia. Some are evergreen; others send up new shoots every year. The stems contain abundant silicate minerals and other minerals. The leaves are merely sheaths that encircle the shoots. An ancient plant, the horsetail’s relatives date to the Carboniferous Period. The common horse¬ tail ( E . arvense) is widespread along streambanks and in meadows in North America and Eurasia. Though poisonous to livestock, horsetails are used in folk medicines. Because of their abrasive stems, some species have been used in polishing tools.
Horta, Victor, Baron (b. Jan. 6, 1861, Ghent, Belg.—d. Sept. 8,1947, Brussels) Belgian architect. From 1892 he designed numerous buildings in Brussels, becoming a leading exponent of the Art Nouveau style. His Hotel Tassel (1892-93) was a pioneering example of the new style. His chief work was the Maison du Peuple (1896-99), the first structure in Belgium to have a largely iron-and-glass facade. From 1912 he directed the Academie des Beaux-Arts, and he designed the Palais des Beaux-Arts
(1922-28).
Horthy \'hor-te\ Miklos (Nagybanyai) (b. June 18, 1868, Ken- deres, Hung., Austria-Hungary—d. Feb. 9, 1957, Estoril, Port.) Hungarian naval officer and regent (1920-44). He served with distinction as a naval commander in World War I and was promoted to admiral in 1918. In 1919 he led an army against the communist regime of Kun Bela . In 1920 the Hungarian parliament voted to restore the monarchy and elected Horthy regent of Hungary, but he thwarted the efforts of Charles IV to recover his throne. He supported Germany in World War II, though his efforts to extri¬ cate Hungary from the war led to his forced abdication and abduction by the Germans in 1944. Released in 1945, he retired to Portugal.
horticulture Branch of agriculture concerned with the cultivation of garden plants—generally fruits, veg¬ etables, flowers, and ornamentals such as plants used for landscaping (see landscape gardening). Propaga¬ tion, the controlled perpetuation of plants, is the most basic horticultural practice. Its objectives are to increase the numbers of a plant and to preserve its essential characteris¬ tics. Propagation may be achieved sexually by use of seeds or asexually by use of techniques such as cutting, grafting (see graft), and tissue culture.
Successful horticulture depends on extensive control of the environ¬ ment, including light, water, tem¬ perature, soil structure and fertility, and pests. Two important horticul¬ tural techniques are training (chang¬ ing a plant’s orientation in space) and pruning (judicious removal of plant parts), used to improve the appearance or usefulness of plants.
See also floriculture.
Horus Ancient Egyptian god with the head of a falcon, whose eyes were the sun and moon. The kings of Egypt were called living incarna¬ tions of Horus. During the 1st dynasty Horus was known princi¬ pally as an opponent of Seth, but after 2350 bc he became associated with the Osiris cult and was identi¬ fied as the son of Osiris. He destroyed Seth, the killer of Osiris, and became ruler of all Egypt. His left eye (the moon) was damaged by Seth but was healed by Thoth. In the Ptolemaic period, the victory of Horus over Seth became a symbol of Egypt triumphing over its occupiers.