IN BRYOLOGICAL WORK. 527 



When my loss of the twelve dozen type slides of the Hypnaceae 

 shook my faith in glycerine jelly I made experiments in search of 

 a substitute, and found an extremely good one in copper acetate 

 combined with glycerine. The formula is given in Squire's 

 Methods and Formulae, but is not referred to any author. It 

 has the advantage of being also a fixing agent : 



Copper acetate 

 Mercury chloride 

 Acetic acid . 

 Glycerine 

 Distilled water 



02 gramme. 



0-4 



0-2 c.c. 

 25-0 

 25-0 



This gives a certain amount of transparency to the cellular 

 structure of the leaves, but it naturally imposes much more 

 labour on the mounter, and is better suited to the microscopist 

 who merely wants mosses for general interest. 



A large number of mosses are so minute that they are quite 

 useless as herbarium specimens, and the only satisfactory way is 

 to possess them mounted as microscopical slides ; such species are 

 Fissidens exilis, F. pusillus, F. viridulus, the majority of the 

 species of the genera Pottia, Ephemerum, Pleuridium, etc. 

 The leaves of these small species are usually very transparent 

 and do not require to be made additionally so by glycerine, even 

 when dilute. Acetate of potash is an admirable mountant for 

 such forms, especially when containing a trace of copper acetate. 

 The following formula has given me satisfaction, it is based on 

 the one Prof. G. S. West recommended for algae : 



Copper acetate O05 gramme. 



Potassium acetate 10 ,, 



Water 25-0 c.c. 



Formalin, 2| per cent, solution, may also be used for these 

 minute, transparent species, but in slides that have been mounted 

 a number of years I have noticed that the formol sometimes 

 precipitates, so that I have been reluctant to use it to any con- 

 siderable extent. On the other hand, many slides in formol 

 appear to have kept perfectly, so that much may depend on the 

 sample of formol used. 



With leaves of such species as Andrea Bothii, which are 

 extremely dark in colour and of leathery consistency, it is im- 



