VI PREFACE. 



owing to difficulties arising as to its publication and the doctor's 

 failing health. 



After his lamented death I began to arrange my notes and 

 drawings, and with the kindly encouragement of the late 

 Dr. Spruce and the help of many good friends, I have been able to 

 bring to a conclusion a work which has occupied the scanty leisure 

 of a busy commercial life. 



My thanks are due to Messrs. James Cash, Richard Crawshaw, 

 George Ely, Symers M. Macvicar, and other friends for help 

 during the progress of the work. 



No one can be more conscious than I am of its many imper- 

 fections, yet I venture to hope that students will find it of value 

 in the study of these interesting plants. 



Wm. Hy. Pearson. 



Park Crescent, Victoria Park, 

 Manchester. 



