OF THE DIATOME.E. 109 



method above described, are those from Tampa Bay, Florida, and the infu- 

 sorial maris from Barbadoes. In the masses from Tampa the lapidifieation is 

 so complete that the alkali destroys the shells before the lumps break up ; 

 and in the case of the Barbadoes marls the cementing material is calcareous, 

 and requires a dilute acid for its removal. In applpng the above process, 

 one caution is necessary, which is to thoroughly Tvash the shells with luater, 

 and not with acids, as the latter ^\ill cause the deposit of a portion of the 

 dissolved silica, and materially injure the beauty of the specimens. A\Tien 

 the washings are no longer alkaline, the specimens may be thoroughly 

 cleansed by acids, or by the chlorate process described above." 



A very ingenious plan of getting transverse and oblique sections of Dia- 

 tomaceous shells is mentioned by Schleiden {Princij)les of Botany, translated 

 by Lanhester, p. 594), which is precisely similar to that for obtaining trans- 

 verse sections of hair, as fii'st given in Pritchard^s Microscojnc Objects. It 

 consists in mixing any veiy pure deposit ^vith mucilage, and, before the 

 mixtiu-e is completely hardened, cutting off delicate slices mth a razor or 

 sharp knife. The preservation of Diatomeae for examination is, on account of 

 their silicious composition, easy ; and it is only in the case of the stalked, fila- 

 mentous, and frondose species that any special arrangements are necessaiy — 

 except, indeed, those demanded in order to mount them as permanent micro- 

 scopic preparations. 



Before the structure of the silicious epiderm can be made out, the endo- 

 chrome of living specimens must be destroyed, which can be effected by heat- 

 ing the frustules on a piece of talc or platinum-foil. But where it is wished 

 to preserve them in a fresh state, so that theii' natural living appearance may 

 as far as possible be retained, immersion in creosote and water is recom- 

 mended by Mr. Shadbolt. Prof Smith, however, finds distilled water supe- 

 rior to any mixture, which is not merely unnecessary, but injurious. " If," 

 .says the author last mentioned, " the filamentous and stipitate forms are not 

 mounted in a fresh state, the fnistules separate from each other, part from 

 their stipes, and lose theii' characteristic appearance. To remedy these in- 

 conveniences, I immerse such specimens as camiot be placed in cells when 

 freshly gathered, in spirits of wine and water, one part of the former to six 

 of the latter ; and their attachment to theii- stipes remains afterwards undis- 

 turbed, unless violence be employed to separate them." 



Fossil, and chemically-prepared and dried specimens are usually preserved 

 in Canada balsam, which is heated and rendered fluid, so that it enters within 

 the cavity of the frastules. The fluidity of the balsam is increased by the 

 addition of a little turpentine or rectified spiiit. The presence of balsam, 

 however, obscures the markings of the silicious epiderm ; and it has been 

 found better, where the resolution or determination of the superficial sculp- 

 turing is very dificult, to moimt the frustules, in a dry state, on a thin 

 object-glass, and under cover of a very thin piece. " To prevent the admis- 

 sion of moisture, which would ultimately make its way to the object and de- 

 stroy its value, it is indispensable that the cover should be cemented to the 

 thin glass below." (Syno2)s. i. p. xxxii.) 



In a collection of Diatomeae, we may, by a magnifier, such as a Coddington 

 lens, select certain specimens from the rest to be moimted. This can be 

 effected, when the size permits, by the projecting terminal hairs of a fine 

 camel-hair pencil, or by the moistened tip of a needle ; but if the sheU be 

 too minute for this, a single stout hair or bristle wiU frequently suffice, and 

 more satisfactorily and readily if the hair be split at the end. Prof. Eedfem, 

 of Aberdeen, pointed out the advantage of split hairs for the purpose, in a brief 

 communication to the J. M. S. 1853, p. 235. He recommends a hair, split 



