IX PTERIDOPHYTES 217 



assume a cylindrical symmetry. On this hypothesis the dorsiventral was 

 the prior state for both the sporophyte and the gametophyte, and the 

 radial the derivative. The author himself states that this " prohepatic " 

 type, from which the two generations were evolved, is still wholly hypo- 

 thetical. As regards the sporophyte, since the embryology gives no 

 countenance to an originally dorsiventral " prohepatic " state, while 

 instances are common of the impress of dorsiventrality upon parts of it 

 originally radial, the theory of Lignier cannot be upheld. It may apply 

 for the gametophyte, but that has nothing to do with our present dis- 

 cussion. It seems the unavoidable conclusion from the facts that the 

 primitive symmetry of the sporophyte was radial. 



