618 STUDIES IN FOSSIL BOTANY 



Lycopods. The record does not go far enough back 

 to show whether this convergence really indicates 

 a common origin for all Pteridophyta from a single 

 stock, though such an hypothesis is quite tenable. 



The question of the ancestry of the Vasculares or of 

 the origin of their characteristic alternation of genera- 

 tions is not as yet directly touched by the palseonto- 

 logical evidence. The general character of the earliest 

 known land-floras, however, and especially the prevalence 

 of megaphyllous types, lends no support to the idea 

 that the spore-bearing plant of the Pteridophytes was 

 ever derived from a sporogonium, whether Bryophytic 

 or otherwise. On the other hand, the evidence, so far 

 as it goes, is perfectly consistent with the hypothesis 

 of the origin of the sporophyte from a branched 

 thallus, a view which has gained ground of late 

 years. 1 



As regards the difficult question of the relation 

 of the Pteridophyta to the Bryophyta, we have no 

 positive evidence from fossil botany, for scarcely 

 anything is known of the history of Bryophytes. One 

 or two supposed Liverworts and Mosses have been 

 recorded from Palaeozoic rocks, but in the absence oi 

 any knowledge of their structure or reproduction the 

 nature of the specimens must remain doubtful. It is 

 remarkable that no remains of Bryophyta have been 

 detected in the petrified material, in which the most 



1 See A. G. Tansley, " Evolution of the Filicinean Vascular System/' 

 New Phytologist Reprint, 1908, Lecture I.; W. H. Lang, "A Theory of 

 Alternation of Generations, based upon Ontogeny," New Phytologist, 

 January 1909. The antithetic view, on the other hand, forms the basis of 

 Professor F. 0. Bower's work, The Origin of a Land Flora, 1908. The 

 present position of the question is illustrated by a discussion at the Linnean 

 Society, reported in the New Phytologist for 1909. 



