156 EVOLUTION OF PLANTS 



etophyte and embryo of Selaginella and the Conifers, 

 are very noticeable, and in connection with Conifer-like 

 Lepidodendrons and other arborescent ancient types, 

 suggest a direct origin for the Conifers from such 

 ancestral forms. 



We see, then, that, starting from a common form, or 

 at least from similar ancestral forms, probably allied to 

 existing liverworts, the three existing classes of Pterido- 

 phytes have developed along parallel lines. In all cases 

 there has been a reduction of the gametophyte among the 

 higher members of each series, with a corresponding 

 perfecting of the sporophyte. This has resulted finally 

 in heterospory, which in at least two cases — i.e. eu- 

 sporangiate ferns and Lycopods — has resulted in the 

 production of seed-bearing plants. In the one case the 

 result was the Angiosperms and perhaps the Cycads ; 

 in the other the Conifers. From the Eusporangiatee 

 were also developed, as a second branch, the modern 

 group of leptosporangiate ferns. 



The accompanying diagram will show the relations of 

 these groups. 



