THE 
MONTHLY MICROSCOPICAL JOURNAL, 
OCTOBER 1, 1870. 
I.—The Patterns of Artificial Diatoms. 
By Henry J. Stack, F.G.S., Sec. RMS. 
(Read before the RoyaL MrcroscopicaL SocrEry.) 
I Hopep by this time to have laid before the Society the results of a 
series of examinations of a number of species of Pinnulariz, show- 
ing that these diatoms have been much misunderstood by micro- 
scopists, who have accepted their separation from the Navicule on 
the ground of their so-called costa not being resolvable into dots, 
or beads. I was led some time since, by carefully viewing the row 
of Pinnularie in Moller’s “type slide” with Beck’s sth, to doubt 
the correctness of the usually-received views, and on repeating the 
investigation with Powell and Lealand’s new immersion {th it be- 
came evident that the costee of most, if not all, were less simple in 
structure than had been imagined, and could be resolved into more 
or less complex beaded forms. An application to Moller, through Mr. 
Baker, for a set of the Pinnularize mounted dry has not yet proved 
successful, probably owing to the disturbance of rational pursuits 
consequent upon the war, and though Mr. Norman supplied some 
excellent slides, he had not in his collection all the species required. 
A general survey of the diatoms in Moller’s “type slide” enables 
a gradation to be traced between beads of large size, widely separated 
under moderate powers, and similar beads closer and closer together, 
until real or closely-approximate contact is obtained. Another grada- 
tion may likewise be traced in size, from beads which are conspicuous 
like little marbles with a magnification of a few hundred diameters, 
to others that appear extremely minute when high powers with 
deep eye-pieces are used for their examination. The question na- 
turally arises, Where does the beading stop? Does it stop at all ? 
A living object immersed in, or supplied with, water having 
silica, or a silicate in solution, and causing, during its life processes, 
a deposition of silica to strengthen its own tissue, must evidently 
obtain it by the method of chemical precipitation, and probably, in 
the case of the diatom, by decomposing a soluble silicate of soda or 
potash. If all diatoms were constructed upon the same principle, 
and by the same process of chemical precipitation, a uniform plan 
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