The Fossil Plants of the Coal Measures. 53 



General, Morphological, and Histological Index to the 

 Author's Collective Memoirs on the Fossil Plants of 

 the Coal Measures. Part i. By William Crawford 

 Williamson, LL.D., F.R.S., &c., Foreign Member 

 of the Royal Swedish Acad. Sc, and of the Royal 

 Society of Gbttingen. 



(Received December 2nd^ i8go.) 



INTRODUCTION. 



My systematic study of the organisation, external and 

 internal, of the Fossil Plants of the Coal Measures, may be 

 regarded as dating from 185 1, in which year I published in 

 the Memoirs of the Manchester Literary and Philosophical 

 Society my paper " On the structure and affinities of the 

 plants hitherto known as Sternbergice." Since the appear- 

 ance of that memoir, a long series of similar publications 

 have embodied the results of my continued researches. 

 The magnitude of the subject, and the scantiness of our 

 information respecting it, led me to adopt a definite line of 

 procedure in publishing my results. Had it been possible, 

 the best method would have been to have worked out 

 whatever appeared to be discoverable about each form of 

 plant, and then to have published the results in a series of 

 special monographs. 



But two difficulties attended the adoption of this method. 

 Firstly, it was impossible to know, at any given point, 

 whether or not I had obtained all discoverable information ; 

 and secondly, what were the chances of life being sufficiently 

 prolonged, after such researches had been completed, to 

 secure the publication of all the results. On the latter 

 point I may express my conviction that even the year 1890 

 would not have seen the commencement of such a publica- 



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