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PLANTAGENET

1501

•PLATJBA

saving those seed-grown plants possessing said traits. The effect of failure to follow the first alternative is seen in the decreasing yield from year to year from selling all the large potatoes of a crop and planting only small ones. Potato-tubers are underground stems, and not "seeds," botanically speaking. Most true seeds tend to reproduce the traits possessed by their parents, i. e., they tend to "breed true.'' By selection we get early maturing corn that ripens in the Dakotas to the Canadian boundary^ and wheat that needs but 15 inches of rainfall. Crossing means that the pollen-dust of one flower has been applied to the pistil or seed-bearing organ of another of a different variety. The result is a hybrid, which may or may not have desirable characteristics, and may or may not be able to transmit any of the desirable characteristics, as can be told only by observing later generations. Cross-breeding always implies selection, but not the reverse. Crossing induces a variation, selection fixes the type. But variations occur without any crossing that we are aware of. Desirable varieties of most fruit-trees, which must be propagated by other means than the seed, appeared >e know not how. Thus the seedless grange was "discovered" in Brazil, the Delaware grape in central Ohio. See Holden's Corn-Culture; Bailey's Plant-Breeding; and U. S. Dept. of Agriculture reports.

Plantag'enet, a family that in 1154, In the person of Henry II, succeeded to the throne of England on the extinction of the Norman dynasty in the male line, and reigned till 1485, when the battle of Bos-worth gave the crown to the house of Tudor. The name comes from planta genista, the broom-plant, which the Angevin ancestor of the family wore in his cap. The Plan-tagenet kings were Henry II, Richard I, John, Henry III, Edward I, Edward II, Edward III, Richard II, Henry IV, Henry V, Henry VI, Edward IV, Edward V and Richard III. See articles under these names. For the great struggle between rival branches of the Plantagenets see ROSES, WARS OF THE.

Plan'tain, species of Plantago, a genus containing more than 200 species, which are distributed everywhere, at least twenty plantains being known in North America. All have a common habit, a rosette-like cluster of basal leaves from the center of which rises a stalk bearing the more or less elongated dense spike of inconspicuous flowers. In the common plantain this spike is often said to resemble a rat's tail. Far the most common species is P. major, the dooryard plantain, which has received numerous other common names. Perhaps the next commonest form is P. lanceolata, known as ribwort, ribgrass and scores of old names.

Plasmo'dium, the naked, protoplasmic body of the slime-molds. It consists of

numerous, fused, naked cells and, like a huge amoeba, has the power of motion. See MYXOMYCETES.

Piaster of Par'is is gypsum (q. v.) prepared for use in the arts, the name arising from the fact that the most famous beds of gypsum in the world are those of Mont-martre near Paris and that the product is shipped from that city. The plaster itself is merely gypsum, the natural bihydrated calcium sulphate, heated and ground fine. In this condition it constitutes a powder devoid of moisture, which has been driven off by heat. But upon the reapplication of water to the mass it rapidly assumes solid form again. This property renders the material invaluable to the designer, who can fill his molds with the moist, soft mass, and presently take it out, set in the form given by the matrix. Dentists use this material in taking casts of the jaws; decorators use it in ornamenting ceilings and cornices; sculptors use it in making the final model from which the marble statue is copied by skilled workmen who make that a profession.

Plastering, the process of covering walls, masonry or woodwork with material which is soft and plastic when applied, but becomes hard when dry. For interior walls a first coat of mortar, made of sand and lime mixed with hair, is generally used. The lime is slaked and, with the other material, is placed in a box. Water is added, and the whole is stirred and kneaded with a hoe until thoroughly mixed and a smooth mortar secured. A thick coat of this mortar is spread with a trowel on the surface of lath or screen, and is pressed in spreading in order that the mortar will be forced through the screen and clinch and hold as the material hardens. This first coat is roughened, to hold the second coat, which is applied when the first is thoroughly dry. The second coat is lighter, containing little or no sand or hair. It is planed smooth ^with a wooden board called a float. The third or setting coat is pure lime, or may be of plasterer's putty and plaster of pans. Cement, staff or stucco is used for exterior walls. See CEMENT.

Plata, Rio de la (re'5 day Id pld'ta), a great estuary in South America between Uruguay and the Argentine Republic. It is about 150 miles long and at Buenos Aires 28 miles wide, but 140 miles broad at its mouth. The northern shore is steep and high, the southern low and flat. The branches of the Plata drain about 1,600,000 square miles, and the outflow, seen for 60 miles out at sea, is about 52,000,000 cubic feet per minute, a volume second only to that of the Kongo. See Sir Horace Humbold's The Great Silver River. See PARANA and PARAGUAY.

Platsea (pld-te'd), a city in Boeotia, on the Borders of Attica and at the foot of Mount Cithaeron, six miles from Thebes. In