CONCLUSION 221 



common with the Pteridosperms that they must 

 ultimately have had the same origin, though 

 their connection with the Fern line of descent 

 was more remote. 



The Horsetails and Sphenophylls show un- 

 mistakable signs of having sprung from a com- 

 mon source. 



Beyond this we cannot go with any safety; 

 we are left with three great races of Vascular 

 Plants: the Ferns, the Lycopods and the joint 

 race of the Horsetails and Sphenophylls. 



It will be noticed that the Lycopods run an 

 isolated course all through; their slight con- 

 vergence with the Sphenophylls in the stem- 

 structure, is scarcely enough to establish any 

 connection. 



As we saw hi the last chapter, the Spheno- 

 phylls may perhaps represent the last remains 

 of an ancient stock, common not only to the 

 Horsetail line but also to other races of the 

 higher Cryptogams. There are so many points 

 of agreement between all these classes that we 

 are led to believe that they must have originally 

 sprung from one ancestral group. This, however, 

 is pure hypothesis. When we get back to the 

 Devonian period, a veil falls, and all the earlier 

 course of evolution (immensely the greater part 

 of the whole history) remains hidden. Scientific 

 men, however, are not always deterred from 



