66 



THE THEORY OF EVOLUTION 



have done so frequently. 1 It would, then, be vain to 

 look for representatives of such types. The presence 

 of a single group of this kind, especially when it is 

 numerically strong, naturally gives to a formation 

 quite a different appearance in comparison with all 

 others in which the group is lacking. 



Fit;. 19. a, CALAMITES Luckowic. &, ASTERO- 

 CALAMTTES scrobiculcttus. Kulm. Astero-cala- 

 mitcs belongs to the Protocalamariacese and 

 shows the course of the furrows as described. 

 (After Gotlmn.) 



If this be borne in mind, then the transformation 

 of the plant world loses much of its ' magnificence/ 



With this preliminary remark we will, by several 

 examples, show of what kind are the transformations 

 observed and to what causes they may be imputed. 



1 As such extinct plant forms there are regarded for instance the 

 Cordaites of the Coal Age, and mostly also the Lepidodendron and Sigillaria 

 and other smaller sections. Steinmann (Die. Gcolog, Grmidlagen der Abstam- 

 mungslelire, 1908, p. 20) will not hear of ' dying out ' in the sense of 

 actual disappearance. Therein he goes too far, since the extinction of 

 extremely specialized forms involves no improbability. 



