10 
Transactions of the Royal Microscopical Society. 
III. — An Essay on the Classification of the Diatomacege. 
By Paul Petit. Translated by F. Kitton, Hon. F.R.M.S.* 
( Taken as read before the Royal Microscopical Society, June 6, 1877.) 
M. P. Petit has favoured me with a copy of his papers (published 
in the ‘ Bulletin de la Societe Botanique de France,’ vols. xxiii. and 
xxiv.) on the classification of the Diatomaceae according to a natural 
system, and has kindly given me permission to introduce the follow- 
ing translation to English microscopists. 
He commences by observing that “ when one wishes to classify 
the Diatomaceae they are met by a great difficulty. Every author 
has his system of classification, but none have constructed a natural 
method. 
“ It would take too long to analyze here the systems of MM. 
Agarah, Ehrenberg, Kiitzing, W. Smith, Meneghini, Grunow, 
Heiberg, Pritchard [the arrangement in Pritchard’s ‘ Infusoria ’ is 
really that of Mr. Ralfs, Rabenhorst, and Pfitzer. To this list 
should be added that of Professor H. L. Smith, of New York, and 
published in the ‘ Lens.’ — F. K.]. 
“ It suffices to say that most of the systems of the authors I 
have cited are constituted on the exterior form of the valves and 
frustules, on the presence or absence of nodules on the surface of 
the valves, or on the mode of growth of the diatoms, i. e. whether 
free or attached to a stipes or imbedded in a gelatinous mass 
having the form of a tube or frond. 
“ We must, however, recognize the fact that M. Grunow f has 
apprehended the affinities of certain genera, and his classification, 
although imperfect, contains many groups that are very natural, 
and which I have adopted. 
“ Long ago the author of the now classic ‘ Synopsis,’ the Rev. 
W. Smith , X had called the attention of observers to the constancy of 
the characters furnished by the endochrome or plasma, colouring the 
frustules : it presents itself under two conditions, sometimes as a 
layer attached to the inner surface of the cell, sometimes consisting 
of granules irregularly disposed or radiating from a central point. 
At the commencement of each of the two volumes of the ‘ Synopsis ’ 
he gives coloured figures of a great many species filled with endo- 
chrome. The figures of W. Smith are much more exact than those 
of Ehrenberg in his great work on the Infusoria. § The remarks 
* This paper was sent by Mr. Kitton to the Royal Microscopical Society, but 
the rules of the Society forbid the reading of translations of foreign memoirs. 
t ‘ Verhandlungen der K. K. zool. bot. Gesellschaft.’ Wien, 1860, 1862, and 
1863. 
J W. Smith, ‘ Synopsis British Diatomaceae,’ vol. ii. p. xxv. 
§ ‘ Die Infusionsthierchen.’ 
