CYCADALES 



159 



already progressed so far that it suggests the Cycas revoluta type. 

 In Lygmopteris, the tips of leaflets are regularly sterile, while the 

 seeds are borne farther back. In Neuropteris, while many of the 

 seeds are terminal, some are lateral. From such a type, both the 



173 



174 175 



Figs. 173-175. — Theoretical form (fig. 173) which might have given rise to the 

 Bennettitales by the abortion of lateral ovules (fig. 174), and to the Cycadales, by the 

 abortion of terminal ovules (fig. 175). 



Cycadales and Bennettitales condition could be derived; the Cyca- 

 dales by the abortion of the terminal sporangium, and the Bennet- 

 titales by the loss of the lateral sporangia (figs. 171, 172). 



We can imagine that the ancestor of both the Bennettitales and 

 the Cycadales looked something like fig. 173. Inside the crown of 



