PREFACE. 



While embodying in this book the results which 

 I have accumulated during the past twenty years, 

 I should like to take the opportunity of thanking 

 the many friends who have assisted me. The 

 first to do so were Mr. Carruthers and Professor 

 A. G. Nathorst, whose work, in fact, led me to 

 undertake these studies. In the troublesome work 

 of determining the plants I have been greatly aided 

 by the constant courtesy and assistance of the 

 officers of the Botanical Department of the British 

 Museum, especially of my friends Mr. E. G. Baker 

 and Mr. A. B. Rendle. At Kew also I have 

 received every facility for the work, and to Mr. 

 J. G. Baker, the late keeper of the Herbarium, I 

 owe much. Messrs. G. and H. Groves have also 

 assisted me at various times with specimens of 

 recent plants which I was unable to obtain for 

 myself, and others have been received from 

 friends whose names are too numerous to mention. 

 With regard to the geological material that I 

 have obtained from others, specimens have been 



