[ 46 



CHAPTER IV 



A DISCUSSION OF THE NATURE AND 

 AFFINITIES OF THE PSILOPHYTON FLORA 



The earlier conclusions as to the affinities of Psilophyton and 

 other members of that flora, advocated enthusiastically and 

 primarily by Dawson, and followed by some other workers, 

 need not detain us here. Dawson's ^ frequently repeated assertion 

 that Psiloijhyton and Parka in particular were related to the 

 Hydropterideae, or so-called Rhizocarps, was regarded by many 

 with grave suspicion, even at the time when no rival theory of 

 affinity was in the field. It is only necessary to add that all the 

 more recent work, especially the most recent studies of all 

 relating to these genera, has not produced, at any rate in our 

 opinion, one particle of evidence in favour of Dawson's con- 

 clusions as to affinity. In fact it may now be said that, whatever 

 views one may hold on this question, it is at any rate certain 

 that these plants were not related to the Water Ferns. 



In any discussion of the affinities of these plants, the evidence 

 of Psilophyton must stand first. We know now the entire plant, 

 both in the form of impressions and petrifactions, and we are 

 thus in a singularly fortunate position , where questions of 

 affinity are involved. We may first, however, state the views 

 of those who have quite recently contributed so greatly to our 

 knowledge in regard to this genus. 



Halle 2 has no hesitation in regarding Arthrostigma gracile as 

 a microphyllous Pteridophytc, and he extends this conclusion 

 to Psilophyton princeps. He appears to base his conclusions 

 largely on the presence of a true vascular strand in these 

 plants. 



Kidston and Lang have no doubt that " Rhynia and Psilophyton 

 belong to the Vascular Cryptogams or Pteridophyta^" and they 



1 Dawson (1888) and in many other places. 



2 Halle (1916). ' Kidston and Lang (1917), p. 779. 



