524 G. T. HARRIS ON MICROSCOPICAL METHODS 



districts. Boiling the specimen may help matters if it is thought 

 the moss is robust enough to stand the treatment, and some 

 species certainly will. But the application of a stiff camel-hair 

 pencil is always necessary to dislodge the particles that adhere 

 in spite of all soaking and boiling. And when all has been done 

 there is always the victorious residuum to jibe at one's efforts. 

 Many species are so fragile that any attempt at cleaning beyond 

 the most superficial seriously injures the specimen ; such is the 

 case with those species having highly papillose leaves in fact 

 such leaves are rarely found perfect, so easily do the papillose 

 cells break away from each other. It is obvious that the 

 question of cleaning the material is a serious tax on the time of 

 the bryologist, and that there really is a valid excuse for his 

 mounts not being the immaculate objects usually achieved by 

 the microscopist. 



Another cause contributing to indifference in bryologists' 

 slides is the necessity that exists for accomplishing a considerable 

 amount of work in a short time. The busy systematist spends so 

 much time in the examination and naming of his specimens that 

 the margin of time available for the preparation and mounting 

 of slides to illustrate his species is too meagre to allow of 

 deliberate and painstaking care, hence a slide which* would be 

 better for remounting is allowed to pass if it shows clearly the 

 desirable features. It is without doubt the need for the minimum 

 of trouble in mounting that has caused the majority of bryo- 

 logists to rely on glycerine jelly for obtaining their mounts. At 

 least I have ascertained that many quite eminent workers do 

 rely on this medium, and from what I have heard I fear to their 

 undoing. Some years ago, by great industry, I amassed a 

 considerable collection of slides illustrating the Hypnaceae, 

 spending the leisure hours of an entire winter in doing so, and 

 in twelve months' time I had the pleasant experience of washing 

 them off, as slides so illustrative of lacunae and every phase of 

 cavity were of no use to me. As I had slides mounted in 

 glycerine jelly perfectly good after a lapse of six years, it was 

 obvious that it was not necessarily an unreliable medium, and as 

 I believe it to be the most convenient medium for general work 

 in bryology I give the following hints to novices for what they 

 may be worth. In the first place, the jelly itself must not be 

 made with a hard gelatine. I used Drescher's emulsion gelatine, 



