CONCLUSION 219 



thoroughly investigated. It might help us a 

 good deal if we knew the internal structure of 

 Pseudobornia, which may quite possibly connect 

 the Sphenophylls with the Calamites. However, 

 it seems to be established that species of the 

 genus Sphenophyllum already existed in the Upper 

 Devonian, so we shall have to go further back 

 than that if we are ever to find their ancestors. 

 The problem is extremely interesting, for 

 while the Sphenophylls approach the Ferns in 

 their foliage, in their anatomy they have some- 

 thing in common with the simpler Lycopods. 

 It may be that we are here on the track of a very 

 early race, in which the characters of the differ- 

 ent classes of vascular plants were still to some 

 extent combined, or rather had not yet separated 

 out. If that is so, the Sphenophylls must repre- 

 sent the last survivors of a great group of primi- 

 tive (but not necessarily simple) Spore-plants, 

 which possibly reached its maximum in pre- 

 Devonian times. 



CHAPTER VIII 



CONCLUSION 



THE student of the evolution of plants is 

 placed under a great disadvantage by the short- 

 ness of the fossil record; in this respect he is 



