142 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



to tail off, some groups becoming less diverse and more restricted in 

 geographical range, though as a whole they remained fairly numerous 

 as well as various and ecologically important. It is widely supposed 

 that the Coniferales derived originally from cordaitalean stock. 



\ 

 \ \ 



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\ 



I , il'J ^ 





Fig. 35. — Cordaitales (reconstructed). A, various Cordaitales (about 20 metres 



in height); B, end of a branch of Cordaites with strobiH and a young branch 



(middle, right) ( about J). (Both after Grand'Eury.) 



though we cannot yet be certain of this. And in spite of the aggres- 

 sive nature of some familiar types — such as the Pines and Spruces 

 which still dominate huge tracts, especially of the colder lands — it 

 seems that many others are eking out a rather precarious existence. 



