WHAT IS A DIATOM?

Otago Daily Times, Issue 1120, 24 July 1865, Page 5

WHAT IS A DIATOM?

The following letter has been addressed to the Hdbart Town Mercury by Mr Francis Abbott:—

At the Microscopical Soiree, held at the Museum on the 13th inst, this question was constantly put by persons anxious for information. The crowded state of the room, and every one wishing to see the varied ohjects exhibited under the microscopes, rendered it impossible to give such information as the question required. About fifteen years ago the Professor of Natural History in the Queen's College, Cork, contemplated commencing a work on the Diatomaceaj; the illustrations lie had to commence upon were four slips of glass labelled "Aberdeen," "Premnny Peat," " Cantire," and "Loch Mourne;" names now to the initiated " familiar as household words." On the centre of each of these slips was to appearance a little fine dust, which, when held up to the light, flashed with a coruscation of f liry gems, and these were Diatomacea;—a family of confervoid or silicioua algm. The members of this family are singly very minute, and of very peculiarcharactcr found in almost all fresh, brackish, or salt water; sometimes forming an uniform yc-llowish-browu layer at the bottom of the water, or adhering to water plants, decayed stems, stones, &c. They aW> occur among mosses, O3cillatoria;, and on damp ground. The individual cells of the Diatomacea; are called frustules, or testuks, and are furnished with an external coat of silica. The separate valves are of various forma, circular, oblong, elliptical, linear, ssddleshaped, boat-shaped, (navicular), undulate, siimoid, &c, and their broad surfaces exhibit various more or less dtlicate sculpturings and markings in the form of bands, lines either parallel, radiate, or crossing each other, aud doto, or cellular, appearance. These valves, when properly prepared, are of special interest, not only on account of their extreme beauty and symmetry, but because they are used as objects for testing the quality of microscopes. The true position of the Diatomaceaj has for many years been a subject of controversy. By Ehrenbenr, their most distinguished observer, they are considered to be animals, and he ascribes to them stomachs", and a series of complicated internal organs. But nearly all good observers of the present day are of opinion ihat their true place is with the simpler tribes of the vegetable kingdom, in which each individual is a plant by itself, a simple cell; the strongest objection to this view lis that of their independent motion. The nature of their markings is also a disputed point; it has never yet been properly decided whether they are depressions or projections. These beautiful and interesting objects are truly cosmopolitan. The deep sea species may be obtained by dredging, or by treating the alimentary canal of fnhea, mollusca, &c, with strong nitric acid. They are found in the fossil state (forming the fossil infusoria of geologists), occurring in va«t numbers in aq'iatic and marine geological deposits, forming bills, rocks, and various strata; also in peat beds, fossil polishing powders, as tripoli, &c, all of which contain many beautiful species. Almost every mail brings tidings of new and interesting varieties whose beauty and infinitesimal size truly bespeak the wisdom of the Creator.

Onr London Correspondent saya:— " The Bank rate of discount, after ruling for five weeks at 4 per cent, was raised to 4J on the 4th instant; a proceeding inexplicable to those who have not the entree of the Bank parlor. The rate, however, was lowered again yesterday, and it now stands at 4 per cent. Consols have oscillated during the month between 90£ and 91&; the latest quotation is 90|. Commercial failures are frequent and heavy, the most notable being that of Byramjee, Cama and Son, parsee merchants, of Bombay, London, and Liverpool; the failure was announced 17th inst., and the liabilities are reported at four millions sterling." BY ftFLAJSDRESS,