Vlll PREFACE 



Many of the illustrations are reproduced from drawings 

 by my wife : those made from the actual specimens are dis- 

 tinguished by the addition of the initials M. S. I am grateful 

 to her also for some improvements in the letter-press. For the 

 drawings made from sections and for some of the outline 

 sketches I am responsible. I have availed myself freely of 

 the facilities afforded by Professor McKenny Hughes in the 

 Sedgwick Museum of Geology for the examination of speci- 

 mens under the charge of Mr Newell Arber, the University 

 Demonstrator in Palaeobotany. It is a pleasure to add that, 

 as on former occasions, I am indebted to the vigilance of the 

 Readers of the University Press for the detection of several 

 errors which escaped my notice in the revision of the proofs. 



A. C. SEWARD. 



Botany School, Cambridge. 

 March 12, 1910. 



