532 G. T. HARRIS ON MICROSCOPICAL METHODS 



separation of which was no great strain on one's mental powers. 

 At the present time it is useless to touch the group unless you 

 are prepared to distinguish between at least forty species, with 

 an average of four varieties each. Of Sphagnum acutifolium 

 alone Warnstorf describes sixty varieties, and I believe that very 

 few even critical bryologists would care to rely on their own 

 diagnosis of them. It will be seen from this how valuable an 

 authenticated collection of slides would be to the bewildered 

 student. 



It will perhaps be desirable to state that the nomenclature 

 adopted in naming the slides is that of the second edition of 

 Dixon's Student's Handbook of British Mosses. 1 believe that 

 Dr. Braithwaite's magnificent monograph is in the library of the 

 Quekett Microscopical Club, and my first intention was to take 

 that as my guide j but Dixon's Handbook is now so generally 

 used, and is so compact, that it would probably be the book 

 selected by any one who decided to take up the study of the 

 mosses ; and I may say that the critical comparisons in it 

 between closely allied species are extremely useful to the student 

 working alone. 



