XLIV] GYMNOSPERMOUS WOOD 167 



plants which in the Permo-Carboniferous era had already advanced 

 far beyond the simple ancestral forms which the botanist seeks 

 but rarely finds. 



The various examples of fossil genera founded on the anatomical 

 features of vegetative organs are dealt with in a separate section 

 and not included with impressions in the descriptions of the several 

 families, partly on the ground that it is rarely possible to demon- 

 strate a connexion between the two sets of records and in part with a 

 view to give a more connected account of the results so far derived 

 from a study of petrified wood. Cioss-references to anatomical 

 structure are given in the descriptions of vegetative and repro- 

 ductive organs when there appear to be sound reasons for assuming 

 a generic or family connexion. The classification of woods is at 

 best provisional and the generic characters are far from constant. 

 The main point is that the student cannot afford to neglect this 

 line of enquiry if he desires to obtain a comprehensive view of 

 the changing combinations of structural features preceding their 

 distribution among existing genera. 



A comparison of recent Conifers and Cycads with their Mesozoic 

 representatives brings out very clearly the fact that while on the 

 one hand the modern Cycads differ widely from the Cycadean 

 pe which played a prominent part in Mesozoic floras, recent 

 Conifers on the other hand agree closely in their main features 

 with their Mesozoic ancestors. The Cycads as we know them now 

 re a more recent product of evolution than the Conifers though 

 it by no means follows that the Conifers in the wide sense are 

 the more ancient group. 



FOSSIL GYMNOSPERMOUS WOOD (Coniferales). 



The earliest attempts to identify petrified wood are summarised 

 >y Goeppert 1 , Knowlton 2 , and other authors. Luidius (Lhwyd) 3 

 it the end of the seventeenth century employed the general desig- 

 lation Lithoxylon, and the termination -xylon is still used in generic 

 names applied to fossil wood in conjunction with some prefix im- 

 plying agreement in the more important anatomical features 

 with some recent genus or family. For woods exhibiting a 

 combination of characters unknown in existing genera a distinctive 



1 Goeppert (50). 2 Knowlton (89 2 ) ; Gothan (05). 3 Luidius (1699) A. 



:; 



