THE EVOLUTION AND PHYLOGENY OF THE GROUP 



In any investigation there is a temptation to indulge 

 in speculation and philosophy. I have tried to keep the 

 preceding chapters largely descriptive, thinking it best 



not to mix actual observations 

 with theoretical considerations. 

 In the following pages I have 

 drawn some conclusions which 

 seem to be warranted by the 

 facts, and have ventured 

 cautiously into the domain of 

 theory. 



Since many organs, Hke the 

 sporophyll, can be traced from 

 the Paleozoic through the 

 Mesozoic, and through the 

 living forms, trends in evolu- 

 tion can be studied with more 

 contidence in the cycads than 

 in groups not favored with 

 such long and well-known 

 Fig. 7 8. — Diagram of geological records. A diagram 



geoloincal horizons. . , i • i i • 



of the geological horizons, 

 together with the position of the cycads and their 

 ancestors, and" also the Bcnnettitales (the "fossil 

 cycads" of Wieland) will help those who arc not 

 familiar with paleobotany (Fig. 78). 



