2 INTRODUCTION. 



kingdom have been traced back to the old formations, and the genetic 

 relations of extinct groups to those now existing and to their progenitors 

 have been discovered. The filiation has actually been already traced a long 

 way backwards in the case of single genera or cycles of affinity, and results 

 have been obtained by Heer l in the case of the Salisburieae, and in that of 

 the Gymnosperms generally by the incomparable works of Grand' Eury 2 

 and Renault 3 on Cordaites, which are invaluable as aids to phylogenetic 

 determinations. 



But though the way has been thus clearly pointed out for palaeophy- 

 tological research in various directions, yet it follows from what has been 

 said that it is at present necessary to keep the different points of view 

 distinctly separate from one another. Hence it is that the present work 

 is strictly confined to the stand-point of the systematist, being intended to 

 show to botanists in a perspicuous form and after application of the neces- 

 sary criticism to what extent the efforts of palaeophytologists have furthered 

 the completion of the Natural System. It will be advisable that the 

 systematic treatment of the material should be preceded by a short exposi- 

 tion of the methods of palaeophytological research as well as by a notice 

 of the mode of preservation of fossil remains, notwithstanding that the 

 greater part of what can be said on these points will be found set forth in a 

 masterly manner in Unger's work 4 . 



Since fossil plants reached the place of their deposit in almost all cases 

 in comparatively small fragments, the first object always is to determine 

 the manner in which these fragments, these branches, leaves, fruits, belonged 

 to one another. It would be a similar task to reconstruct a forest from the 

 mud of a piece of water into which the dead parts of the trees have fallen. 

 In these circumstances we can only certainly conclude that separate parts 

 belong to one another in two cases : first, if they occur once and excep- 

 tionally in union with one another ; secondly, if they exactly resemble one 

 another in characteristic 'features of anatomical structure. Simple as this 

 appears at first sight, yet various circumstances occur in practice to make 

 the very greatest circumspection necessary in applying both these criteria. 

 In the case of a specimen showing parts in connection with one another 

 which are usually separate, since we are dealing in most cases with impres- 

 sions of plants, we have to make quite sure in each several instance that 

 there is no third formless object lying over two distinct but converging 

 remains in such a manner as to bring about an apparent connection between 

 them. Mistakes have as a matter of fact often arisen in this manner. With 

 regard to the establishing the anatomical identity of two separate fragments, 

 it must be remembered that this presupposes an exact knowledge of the 



>Heer(l'. f Grand* Eury (1). ' Renault (11. ' linger (8.1. 



