DESMIDS, DIATOMS, AND FRESH-WATER AhGM. 85 



the Algae, the following solution will be found to be 

 an excellent medium. In it the plants retain their 

 green color for a long time, and the cell-contents have 

 less tendency to shrink from the cell- 

 wall than with any other of the many 

 media often recommended. Any 



^'^BrebUs6nii''"" ^ruggist Can make the solution. It is 

 composed as follows: Camphorated 

 water and distilled water, of each, 50 grammes; glacial 

 acetic acid, 0.5 gramme; crystallized chloride of 

 copper, and crystallized nitrate of copper, of each, 2 

 grammes; dissolve and filter.- The solution was origi- 

 nally devised by M. Petit, a French microscopist. 



The plants should be placed in a cell made of shel- 

 lac, a few drops of this preservative copper-solution 

 added, and the coyer fastened down with shellac. If 

 any other cement, except perhaps Brown's rubber-ce- 

 ment, is used with this solution it will inevitably run 

 under and ruin the preparation. 



If the reader should find the desmids so pleasing 

 that he desires to study them rather than to learn the 

 names and appearance of a few of the commonest as 

 here given, he should refer to the Rev. PVancis 

 Woile's monograph, entitled "The Desmids of the 

 United States," and to Stokes's "Fresh-water Algs 

 and the Desmidieae of the United States," the latter 

 being an extended, mostly artiScial, key to the genera 

 and the species of these attractive plants, founded on 

 Woile's classification. 



II. DIATOMS. 



For a long time there was much discussion as to the 

 animal or vegetable nature of the diatoms, but that 

 they are plants is now the general belief. Their 



