PrRE PACE. 
—039{00=——— 
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 
2-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. 
