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 Eusporangiate 
were also developed, as a second branch, the modern 
group of leptosporangiate ferns. 
The accompanying diagram will show the relations of 
these groups. 
