164 MOSSES AND LIVER.WOETS 



moss is very dry, or if it is one in which the 

 leaves grow thickly on the stem, to boil it for 

 a minute or so in a test-tuhe, over a spirit-lamp, 

 so as to aid in expelling the air, or to soak it for 

 some time in water which has heen allowed to boil 

 for ten minutes or a quarter of an hour, and which 

 consequently contains comparatively little air. The 

 specimen, while still in the water, must he cleansed, 

 as far as may he, from impurities, and freed from 

 air, by means of a camel's-hair brush and the 

 dissecting-needles. Too much time and attention 

 cannot be given to this somewhat tedious process, 

 as the success of the mount very largely depends 

 upon the thoroughness with which it is effected. 



The specimen, when thus sufficiently washed, 

 has still to be subjected to a further preliminary 

 treatment, for if at once immersed in the mounting 

 medium the effect would be to curl up the leaves 

 beyond recognition. A very simple, and in many 

 cases most effective, way of avoiding this is to 

 place it in a teaspoonful of water in which three 

 or four drops of glycerine have been mixed, and 

 then to boil over a spirit-lamp for a few seconds ; 

 by this means the glycerine more or less takes the 

 place of the water in the cells, and the leaves 

 may then be safely mounted. In the larger- 

 celled and consequently more "filmy" plants, 

 however, this process is not sufficient, and the 

 plant must then be soaked for twenty-four hours 

 in a preparatory mixture composed as follows : 



