A paper on Diatoms was read by Mr. J.M. Kirk.

Diatoms have long been considered to be the remains of animalcules and most of the older microscopists treated them as such. Although the question is far from being settled, they are now generally considered as belonging to the vegetable kingdom. Diatoms, like Desmids, are simple cells having a firm outer coating within which is enclosed an endochrome. The diatomacia are divided into two chief groups – those which are single frustules and those which colure in masses.

The name seems to have been given to them from the readiness with which the latter may be cut or broken through, hence they are some times called “brittle worts”. During the healthy life of a Diatom the process of self-division is continually being repeated and a very rapid multiplication of frustules then takes place, all of which are repetitions of the same individual form. These original forms are of great variety.

A large part of the infusorial earths deposited at the bottom of lakes is composed of diatoms, one such remarkable deposit being the tripoi or rottenstone used for polishing metals. The well known “Turkey Stone”, and the material called “Silicon” now sold for cleaning jewelry, are similarly composed. Such is the abundance of Diatoms in some rivers and estuaries that their rapid increase is affirmed by Chrenberg to have exercised an important influence in blocking up harbors and diminishing the depth of channels.

It is affirmed by Hookes that the universal presence of this invisible vegetation throughout the South Polar Ocean is a most important feature since there is a marked deficiency in this region of higher forms of plants, and were it not for them, there would be neither food for aquatic animals, nor (if it were possible for these to maintain themselves by preying on one another) could the ocean waters be purified of the Carbonic Acid which animal respiration would be continually imparting to them. A diatomaceous deposit is met within Norway & Sweden under the name of Bergmeld or mountain flour, and in times of scarcity the inhabitants mix this with their dough in making bread.

Mr. Kirk explained the method for collecting, preserving & mounting the various diatoms, and illustrated his paper by a large number of beautifully executed drawings of typical forms, among the more elaborate of which may be mentioned the representations of Arachnoidiscus, Heliopelta, and Isthmia.