54 



THE THEORY OF EVOLUTION 



To all appearance there also already existed in the 

 Silurian era the predecessors of the Sigillaria (which 

 developed later so richly in the Carboniferous) (Figs. 12 

 and 13) in the form of Bothrodendrse, if the age of the 



localities of the finds (Harz) be 

 correctly estimated. 



Even Grymnosperms are found 

 already in the group of Cordaitae l 

 which also play a very prominent 

 role in the Carboniferous system. 



(2) The further development of 

 the flora. 



In the Devonian formation the 



FIG. 12. RECONSTRUCTED 

 SIGILLARIA. 



a. Flower. 6. Leaves. 



st. Rootstock (stigmaria) . 



FIG. 13. PORTION OP TRUNK OF 

 SIGILLARIA SHOWING VARIOUS 

 STATES OF PRESERVATION. 



a. Bark entire. 



b and c. Bark removed. 



discoveries of land or rather marsh plants become 

 already more frequent. With the ferns there appears 

 a further group of the highest Cryptogams, the Proto- 

 calamariacese ; these are the Equisetum trees as yet 

 but few in number and fairly alike among themselves. 



1 Zittel's Handbuch V, p. 251. 



