42 INTRODUCTION. 



inconvenience seems to be completely obviated by the plan 

 I have recommended above. 



" I would remark that the gold-size employed should be 

 of the consistence of treacle ; when purchased it is usually 

 too fluid, and should be exposed for some time in an open 

 vessel, a process which renders it fit for use." 



Mr. Sidebotham also has favoured me with directions for 

 mounting the Desmidiece. His method is nearly similar to 

 that employed by Mr. Thwaites, but when the last coat of 

 varnish is nearly dry, he applies a fine bronze with a camel- 

 hair pencil. This not only has a neat effect, but prevents 

 the risk of adhesion consequent on the softening of the var- 

 nish in warm weather. Mr. Sidebotham uses distilled water 

 as the mounting fluid, but although his specimens retain the 

 green colour of the endochrome better than any other I have 

 seen, yet, for the reason assigned by Mr. Thwaites, I doubt 

 whether such a mode is suitable for their permanent preser- 

 vation. 



Mr. Thwaites' fluid is superior to camphorated- water and 

 various other liquids which I have tried ; but as it requires 

 more time for its preparation than may be at all times con- 

 venient, I find the following the best substitute : — 



Bay -salt and alum, one grain each, dissolved in an ounce 

 of distilled water. 



Goadby's solution acts too powerfully on freshwater Algae, 

 and corrosive sublimate injures the specimens. 



In mounting the Desmidieee great attention is necessary to 

 exclude air-bubbles, which cannot be avoided unless the fluid 

 completely fills the cell ; and also not to use too much fluid, 

 as in this case the smaller species will often be washed away 

 on the escape of the superfluous portion. 



As the cells cannot be sealed whilst any moisture remains 

 on their edge, it should be removed by blotting-paper, which 

 is preferable to any other mode. 



The thin glass manufactured for the purpose is preferable 

 to talc for covering the specimen, and should always be used 



