Page:EB1911 - Volume 22.djvu/16

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POLLARD—POLLINATION

POLLARD, EDWARD ALBERT (1828–1872), American journalist, was born in Nelson county, Virginia, on the 27th of February 1828. He graduated at the university of Virginia in 1849, studied law at the College of William and Mary, and in Baltimore (where he was admitted to the bar), and was engaged in newspaper work in California until 1855. In 1857–1861 he was clerk of the judiciary committee of the National House of Representatives. By 1859 he had become an outspoken Secessionist, and during the Civil War he was one of the principal editors-of the Richmond Examiner, which supported the Confederacy but was hostile to President Jefferson Davis. In 1864 Pollard sailed for England, but the vessel on which he sailed was captured as a blockade runner, and he was confined in Fort Warren in Boston Harbour from the 29th of May until the 12th of August, when he was paroled. In December he was placed in close confinement at Fort Monroe by order of Secretary Stanton, but was soon again paroled by General B. F. Butler, and in January proceeded to Richmond to be exchanged there for Albert D. Richardson (1833–1869), a well-known correspondent of the New York Tribune, who, however, had escaped before Pollard arrived. In 1867–1869 Pollard edited a weekly paper at Richmond, and he conducted the Political Pamphlet there during the presidential campaign of 1868.

His publications include Black Diamonds Gathered in the Darkey Homes of the South (1859), in which he advocated a reopening of the slave trade; The Southern History of the War (3 vols.: First Year of the War, with B. M. DeWitt, 1862; Second Year of the War, 1864; Third Year of the War, 1864); Observations in the North: Eight Months in Prison and on Parole (1865); The Lost Cause (1866); Lee and His Lieutenants (1867); The Lost Cause Regained (1868), a southern view of reconstruction urging the necessity of white supremacy; The Life of Jefferson Davis (1869), an arraignment of the Confederate president; and The Virginia Tourist (1870).

POLLENTIA (mod. Pollenzo), an ancient town of Liguria, Italy, 10 m. to the north of Augusta Bagiennorum, on the left bank of the Tanarus (mod. Tanaro). Its position on the road from Augusta Taurinorum to the coast at Vada Sabatia, at the point of divergence of a road to Hasta (Asti) gave it military importance. Decimus Brutus managed to occupy it an hour before Mark Antony in 43 B.C.; and it was here that Stilicho on the 29th of March 403 fought the battle with Alaric which though undecided led the Goths to evacuate Italy. The place was famous for its brown wool, and for its pottery. Considerable remains of ancient buildings, an amphitheatre, a theatre and a temple still exist. The so-called temple of Diana is more probably a tomb.

See G. Franchi-Pont in Atti dell' academia di Tornio (1805–1808), p. 321 sqq.

POLLINATION, in botany, the transference of the pollen from the stamen to the receptive surface, or stigma, of the pistil of a flower. The great variety in the form, colour and scent of flowers (see Flower) is intimately associated with pollination which is effected by aid of wind, insects and other agencies. Pollen may be transferred to the stigma of the same flower—self-pollination (or autogamy), or to the stigma of another flower on the same plant or another plant of the same species—cross-pollination (or allogamy). Effective pollination may also occur between flowers of different species, or occasionally, as in the case of several orchids, of different genera—this is known as hybridization.

The method of pollination is to some extent governed by the distribution of the stamens and pistil. In the case of unisexual flowers, whether monoecious, that is, with staminate and pistillate flowers on one and the same plant, such as many of our native trees—oak, beech, birch, alder, &c., or dioecious with staminate and pistillate flowers on different plants, as in willows and poplars, cross pollination only is possible. In bisexual or hermaphrodite flowers, that is, those in which both stamens and pistil are present, though self-pollination might seem the obvious course, this is often prevented or hindered by various arrangements which favour cross-pollination. Thus the anthers and stigmas in any given flower are often mature at different times; this condition, which is known as dichogamy and was first pointed out by Sprengel, may be so well marked that the stigma has ceased to be receptive before the anthers open, or the anthers have withered before the stigma becomes receptive, when cross pollination only is possible, or the stages of maturity in the two organs are not so distinct, when self-pollination becomes possible later on. The flower is termed proterandrous or proterogynous according as anthers or stigmas mature first. The term homogamy is applied to the simultaneous maturity of stigma and anthers. Spontaneous self-pollination is rendered impossible in some homogamous flowers in consequence of the relative position of the anthers and stigma—this condition has been termed herkogamy. Flowers in which the relative position of the organs allows of spontaneous self-pollination may be all alike as regards length of style and stamens (homomorphy or homostyly), or differ in this respect (heteromorphy) the styles and stamens being of different lengths in different flowers (heterostyly) or the stamens only are of different lengths (heteranthery). Flowers which are closed at the time of maturity of anthers and stigmas are termed cleistogamous.

EB1911 Pollination - long and short-styled flowers of Primula sinensis.jpg
(From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.)

Fig. 1.—Long-styled, L, and short-styled, K, flowers of Primula sinensis.

G, Level of stigma; S, level of anthers; P, N, pollen grains and stigmatic papillae of long-styled form; p, n, ditto of short-styled form.

Self-pollination is effected in very various ways. In the simplest case the anthers are close to the stigmas, covering these with pollen when they open; this occurs in a number of small annual plants, also in Narcissus, Crocus, &c. In snowdrop and other pendulous flowers the anthers form a cone around the style and the pollen falls on to the underlying stigmas, or in erect flowers the pollen may fall on to the stigmas which lie directly beneath the opening anthers (e.g. Narthecium). In very many cases the pollen is carried to the stigma by elongation, curvature or some other movement of the filament, the style or stigma, or corolla or some other part of the flower, or by correlated movements of two or more parts. For instance, in many flowers the filaments are at first directed outwards so that self-pollination is not possible, but later incline towards the stigmas and pollinate them (e.g. numerous Saxifragaceae, Cruciferae and others), or the style, which first projects beyond the anthers, shortens later on so that the anthers come into contact with the stigmas (e.g. species of Cactaceae), or the style bends so that the stigma is brought within the range of the pollen (e.g. species of Oenothera, Epilobium, most Malvaceae, &c.). In Mirabilis Jalapa and others the filaments and style finally become intertwined, so that pollen is brought in contact with the stigma. Self-pollination frequently becomes possible towards the end of the life of a flower which during its earlier stages has been capable only of cross-pollination. This is associated with the fact, so ably demonstrated by Darwin, that, at any rate in a large number of cases, cross-pollination yields, better results, as measured by the number of seeds produced and the strength of the offspring, than self-pollination; the latter is, however, preferable to absence of pollination. In many cases pollen has no effect on the stigma of the same flower, the plants are self sterile, in other cases external pollen is more effective (pre-potent) than pollen from the same flower; but in a very large number of cases experiment has shown that there is little or no difference