Diatom a

( Bot.) A genus of plants, order DIATO MACER, q. v. Diatom a'cesæ, n. pl. ( Bot.) The Brittle-worts, an order of plants, alliance Algales. - DIAG. Crystalline, angular, fragmentary bodies, brittle, and multiplying by spontaneous separation. This group of Algæ, of low organization, and including the Bacillar i a, is remarkable for the large quantity of silex which they contain. Vast beds occur, many feet in thickne , consisting entirely of effete frustules, as the separate joints of the fronds are called. These beds are known by the name of Tripoli, and afford an admirable article for polishing. They occur again in the form of white powder, known as Mountain Meal, which is mixed with flour in some parts of Sweden. The D. form a large portion of the food of some of the lower molluscs. They occur in all parts of the world, enduring extreme degrees of cold without annihilation, and are found also in springs of high temperature.