The Structure of Diatoms. By Br. J. E. L. Flogel. 509 



delicate objects. As an example, I may mention a bundle of 

 P. Icdticum in my possession in 150 sections, of which 100 were 

 successful ; of these about 70 could be identified as being from one 

 liustule. 



Preservation of Preparations. — This subject is unfortunately 

 for me at the present moment one of the most troublesome. One 

 would anticipate that by taking quite dry gum imbedded in balsam 

 slowly hardened, the preparation would be almost indestructible. 

 I regret to say this is not always the case. My preparations 

 of 1869 remained stable six to seven years. But afterwards 

 a fatal change took place with many. The sharp straight edges 

 of the gum-chips lost their sharpness, the edges rounded ofi", and 

 lastly a kind of oil-drop took their place, in which the former 

 beautiful sections almost disappeared. Whether my present house 

 is too damp, or whether moisture works through the balsam along 

 the glass up to the sections, I do not know ; but I suspect some- 

 thing of the kind. The serials I made last June and July have 

 kept in partibus well up to the present, but a portion commenced 

 in October to change, although as a protection I had covered the 

 edges with asphalt and kept them in a room which was warmed 

 eveiy day. The real cause of the destruction of these preparations 

 is still a mystery, and I would recommend that sections should 

 be studied immediately after being made. 



II. Results of the Investigations. 



My first paper was confined to the varieties of Pleurosigma, and 

 I now give an account of all the other diatoms the structural details 

 of which I have investigated. I may at once say that a general 

 sketch of diatom sculpture cannot be given. We cannot take the 

 structure discovered by me in Pleurosigma (consisting of chamber- 

 like holes in the interior of the cell-membrane) and thus explain the 

 structure of all diatoms, nor can we conclude from Moller's proved 

 structure of Trieeratium (viz. chambers open externally) that this is 

 the same, mutatis mutandis, with all others of this numerous order. 



1. Pinnularia. 



Probably the cellular envelope of a great number of diatoms 

 follows the type of Pinnularia, which may therefore be put first, all 

 the more so since the views regarding their structure (chiefly based 

 on Pfitzer) adopted in most text-books, are totally erroneous. 

 Moreover, the structure of their cell- walls is very remarkable. For 

 my material (Pinnularia major) I have again to thank Herr J. 

 L). Moller. It consisted principally of isolated valves which we)e 



