diatomaceæ

Century Dictionary and Cyclopedia

1. An order of microscopic unicellular algæ, much resembling the Desmidiaceæ, from which they are distinguished by a silicification of the cell-wall and by the presence of a brownish pigment which conceals the green of the chlorophyl. The cells are either isolated or united into threads, etc., and often secrete a thin jelly in which they live socially. Each frustule is composed of two separate and similar parts (valves), the edges of which usually lit one over the other like the lid of a box. Reproduction takes place, as in two ways, by division and by sexual conjugation. Diatoms exist in all parts of the world inimmense numbers at the bottom of the sea and of fresh water, and are also found attached to the submerged parts of aquatic plants. etc., and among mosses and in other damp localities! There are many genera, and the number of known species exceeds 1,500. They vary greatly in the form and markings of the valves, which are often exquisitely sculptured, forming beautiful objects under the microscope and testing its highest powers. In some species the lines are found to equal 125,000 to the inch. Extensive fossil deposits of the silicious remains of Diatomaceœ; occur in various localities, as at Bilin in Bohemia, and in Virginia, Nevada, and California. They are sometimes used as polishing powder. They are abundant in guano. Also called Bacillariaceæ.