Dicotyledon (dī-kot-i-le´don), a plant whose seeds are readily recognized by the embryo containing a pair of cotyledons or seed-leaves, which are always opposite to each other. Dicotyledons are further characterized by their netted-veined leaves and their 'open' vascular bundles containing a cambium; the parts of the flower are commonly in fours or fives. In Bentham and Hooker's system the class is divided into four subclasses—Thalamifloræ, Calycifloræ, Corollifloræ, and Monochlamydeæ. Engler's system recognizes only two subclasses, viz. Archichlamydeæ and Sympetalæ.
Dictaphone, an adaptation of the gramophone, in which the principle of that invention is applied to the requirements of modern business. Letters or memoranda are spoken into the machine, which 'records' them on waxen cylinders. The machine is then passed on to a shorthand writer or typist (or the cylinder may be transferred to a duplicate machine), and the recorded matter is dictated. The
motive power is electricity; the speed of dictation is capable of adjustment to that of the writer; and by means of an accessory machine the records can be scraped and re-used.
Dicta´tor, an extraordinary magistrate of the Roman Republic, first instituted B.C. 501. The power of naming a dictator, when an emergency arose requiring a concentration of the powers of the State in a single superior officer, was vested by a resolution of the Senate in one of the Consuls. The dictatorship was limited to six months, and the person who held it could not go out of Italy. This rule was laid aside during the first Punic War. The dictator was also forbidden to appear in Rome on horseback without the permission of the people, and he had no control over the public funds without the permission of the Senate. He had the power of life and death, and could punish without appeal to the Senate or people. All the other magistrates were under his orders. Originally the dictator was a patrician, but in 356 B.C. the plebeian Marcius Rutilus was called upon to fill the office of dictator. The term is now often applied to rulers enjoying or exercising extra-constitutional power.—Cf. A. H. J. Greenidge, Roman Public Life.
Dictionary (from the Lat., dictio, a saying, expression, word), a book containing the words, or subjects, which it treats, arranged in alphabetical order. It may be either a vocabulary, or collection of the words in a language, with their definitions; or a special work on one or more branches of science or art prepared on the principle of alphabetical arrangement, such as dictionaries of biography, law, music, medicine, history, or philosophy. Amongst dictionaries of the English language, the earliest seem to have been those of Bullokar (1616) and Cockeram (1623). That of Dr. Johnson, published in 1755, made an epoch in this department of literature. Previous to this the chief English dictionary was that of Bailey, a useful work in its way. An enlarged edition of Johnson's dictionary, by the Rev. H. J. Todd, appeared in 1818; and this, again enlarged and modified, was issued under the editorship of Dr. R. G. Latham (1864-72). The best-known American dictionary of the English language is that by Noah Webster, published in 1828, and since entirely recast. Richardson's dictionary, published during 1836 and 1837, was valuable chiefly for its quotations. Ogilvie's Imperial English Dictionary, based on Webster, and first published between 1847 and 1850, has been issued in a remodelled and greatly enlarged form (4 vols. 1881-2 and subsequently, Charles Annandale, LL.D., editor). It is one of the encyclopædic dictionaries. Cassell's Encyclopædic Dictionary is another extensive work (1879-88). The largest completed English dictionary is the Century Dictionary (New York, 1889-91, 6 vols. quarto). The Standard Dictionary is another American work. A new English dictionary 'on historical principles', first edited by Sir J. A. H. Murray, LL.D., with the assistance of many scholars, and now edited by Dr. Henry Bradley, is being published at the Clarendon Press since 1884. Among foreign dictionaries are the polyglot dictionary of Calepino (1502), the Latin and Greek Thesaurus of Robert and Henry Stephanus, the Italian Vocabulario della Crusca (1612), &c. The chief etymological dictionary of English words is that by Professor Skeat (1882). Among French dictionaries (for French people) the chief is that of Littré; among German, the dictionary begun by the brothers Grimm.
Dictyotaceæ, a family of Brown Algæ, section Cyclosporeæ. Dictyota dichotoma, with a delicate, flattened, repeatedly forked thallus, is not uncommon in sandy pools on our coasts. The plants are of three kinds, viz. ♂, bearing antheridia; ♀, bearing oogonia; and neuter, producing tetraspores. The oospores give rise to neuter plants, the tetraspores to ♂ or ♀ plants. This is one of the best instances of 'homologous' alternation of generations, i.e. that type in which the different generations are identical in form, differing only in their reproductive organs and in the number of chromosomes in their nuclei. Another genus is Padina.
Didactic Poetry, that kind of poetry which professes to give a kind of systematized instruction on a definite subject or range of subjects. Thus the Georgics of Virgil and the De Rerum Natura of Lucretius profess to give, the one a complete account of agriculture and kindred arts, the other a philosophical explanation of the world. Other examples of purely didactic poetry are Horace's Ars Poetica, and Pope's Essay on Criticism. In a larger sense of the word most great poems might be called didactic, since they contain a didactic element in the shape of history or moral teaching, Dante's Divina Commedia, Milton's Paradise Lost, or Goethe's Faust, for example. The difference may be said to be this, that in the one case the materials are limited and controlled by nothing but the creative fancy of the poet, while in the other they are much more determined by the actual nature of the subject treated of.
Didel´phia, one of the three subclasses of the Mammalia (the others being Monodelphia and Ornithodelphia), comprising only one order, that of Marsupials or pouched mammals.
Diderot (dēd-rō), Denis, a French writer and philosopher, born in 1713, at Langres, in Champagne, died in 1784. He was educated in the
school of the Jesuits, and afterwards at Paris, at the College of Harcourt, but declined to study law, preferring to earn his living by teaching mathematics. His first works were the Essai sur le Mérite et la Vertu (1745); and the Pensées Philosophiques (1746), a pamphlet against the Christian religion. His Lettre sur les Aveugles à l'Usage de Ceux qui Voyent is in the same strain. These heterodox publications cost him an imprisonment for some time at Vincennes. Diderot now tried writing for the stage, but his pieces were failures. In 1749 he had begun, along with D'Alembert and some others, the Encyclopædia. At first it was intended to be mainly a translation of one already published in English by Chambers. Diderot and D'Alembert, however, enlarged upon this project, and made the new Encyclopædia a magnificently comprehensive and bold account of all the thought and science of the time. Diderot, besides revising the whole, undertook at first the mechanical arts, and subsequently made contributions in history, philosophy, and art criticism. But the profits of all his labour were small, and it was only the liberality of the Empress Catherine, who purchased his library for 50,000 livres and made him a yearly allowance of 1000 livres, that saved Diderot from indigence. In 1773 he visited St. Petersburg to thank his benefactress and was received with great honour. On his return to France he lived in retirement, passing the last ten years of his life in writing and conversations, wherein, as Marmontel said, he was at his best. Besides his articles in the Encyclopædia he wrote numerous works, some of which were published after his death. Among the best known are Le Neveu de Rameau, a kind of philosophical dialogue which Goethe thought worthy of translation; Essai sur la Peinture, and Paradoxe sur le Comédien, suggestive essays on the principles of painting and acting; two lively tales, La Religieuse and Jacques le Fataliste. On account of his great interest in almost every branch of human knowledge, Voltaire nicknamed him 'Pantophile Diderot'.—Bibliography: T. Carlyle, Essay on Diderot; F. Brunetière, Études Critiques; R. L. Cru, Diderot as a Disciple of English Thought.