PREFACE. 



The papers on which this work is founded were originally com- 

 municated to the Royal Microscopical Society, at the request 

 of one of my friends on the Council ; and it is, therefore, with 

 peculiar pleasure I dedicate it to them, since without the instru- 

 ment which they have done so much to bring to perfection, no 

 satisfactory investigation of the subject would be possible. 



As I have been only able to prosecute it as a relaxation 

 from active professional work, I am aware it must exhibit many 

 deficiencies and shortcomings ; yet the dissections and observa- 

 tions required, have proved to me lessons of the highest value in 

 imparting a knowledge of these interesting plants, which I trust 

 may to some extent be shared in by all who make use of this 

 record of them. 



The drawings of the plants are all of the natural size, and 

 taken from specimens in a moist or expanded state ; the dissec- 

 tions have as far as possible been copied by means of the camera 

 lucida and Messrs. Beck's large instrument with 3 - inch and 

 f-inch objectives, and represent the structural peculiarities which 

 are characteristic of the different species. 



To Professor Lindberg, of Helsingfors, I am deeply indebted 

 for rare specimens and critical observations, and to him and the 

 various correspondents whose names are recorded under each 

 species, I beg to offer my warmest thanks. 



Clapham Rise, London, 

 September, 1878. 



