IN BRYOLOGICAL WORK. 525 



which is an extremely clear but hard gelatine, and this was the 

 principle cause of my disaster. The jelly must contain a good 

 proportion of glycerine. Kaiser's formula appears to be a very 

 good one if home preparation is in view, as it does not set hard. 

 I have slides six years old mounted with it which have suffered 

 no deterioration. The object to be mounted should be soaked for 

 a considerable time in equal parts of glycerine and water (in my 

 own work they always have twenty-four hours) ; unless the 

 structure of the object is thoroughly permeated with the dilute 

 glycerine, lacunae are sure to develop by subsequent absorption. 

 My own experience leads me to the conclusion that a point of 

 great importance in using glycerine jelly so as to ensure reliable 

 mounts, is to avoid mounting the object with the jelly at a high 

 temperature; it should be used at just about the melting-point. 

 If the temperature is high, subsequent contraction is considerable 

 and cavities around the object are not unlikely to make an 

 appearance later on. 



Another point where many mounters err, especially bryolo- 

 gists, is in applying considerable pressure to the cover-glass 

 until the jelly has set, thus pressing out the bulk of the jelly and 

 leaving only a thin film between the slip and cover-glass. It is 

 very nice to have a leaf mounted perfectly flat so that the cells 

 can be studied from apex to base without focusing down through 

 the convexity of the leaf ; but such slides are seldom permanent. 

 The amount of jelly should be sufficient to cover the object ; and 

 it is easy, when constantly using jelly, to guess just about the 

 amount that will cover the object and spread to the edge of the 

 cover-glass when it is placed in position. When the jelly has 

 thoroughly set, if any has escaped beyond the edge of the cover- 

 glass it should be washed away. Personally, I lay the slide 

 aside for about twenty-four hours after mounting, then give it a 

 good scrubbing with a moderately stiff tooth brush under a jet of 

 water. This frees it from all glycerine outside the cover. The 

 slide is then ringed with a plain solution of good hard gelatine, 

 the strength of the solution being immaterial so long as it is not 

 a weak one. When this has set, which it will do quite quickly, 

 it is brushed over with a 10 per cent, solution of chrome alum. 

 At firs-t I used formalin, but found that its indurating action was 

 so great that the ring of gelatine split and peeled off. Chrome 

 alum toughens rather than hardens the gelatine. In its present 



