CONCLUSION 299 



The latter, as at present existing, form three quite 

 distinct stocks, Horsetails, Ferns, and Club Mosses, 

 but in none of the three is there the least evidence for 

 any near relationship to the Bryophytes. The sexual 

 generation presents little difficulty ; for instance, the 

 thallus of a Pellia may well be compared with the 

 prothallus of a Fern. It is the sporophyte which is 

 so different in the two classes. Speaking broadly, the 

 asexual generation in the Bryophyta is always a fruit, 

 while in Vascular Cryptogams it is always a plant. 

 Nothing really approaching an intermediate form 

 between the two kinds of sporophyte has ever been 

 discovered, either among recent or fossil plants. 



Evidently these two great series the Bryophyta 

 and the Pteridophyta diverged very far back indeed. 

 There is no reason to suppose that the sporogonium of 

 a Moss or a Liverwort ever became modified into the 

 asexual plant of a Fern, Horsetail, or Lycopod. The 

 two forms of sporophytes have probably always been 

 different from the first origin of Archegoniatse onwards. 

 There is direct geological proof of the enormous an- 

 tiquity of the Vascular Cryptogams, which, together 

 with certain Gymnosperms, were well developed even 

 in the Devonian period ; their origin is completely 

 lost in the mists of palaeozoic antiquity, and at present 

 we are entirely without any facts which can throw light 

 on the mystery. 



The Pteridophyta are much more highly organised 

 than any of the previous groups ; their advance is 

 entirely confined to the asexual generation, for the 

 oophyte remains throughout at a very low level (below 

 that of the simplest Bryophyta), and indeed degenerates 

 as we reach the higher forms. No doubt the aquatic 



