Ill] 



THURSOPHYTON AND PTILOPHYTON 



31 



are known and that their aspect is remarkably Lycopodian. The 

 lateral organs, in view of the evidence of Psilophyton, we should 

 be inclined to regard as scale-like emergences, though they may 

 have begun to function as leaves. At any rate they do not on 

 the present evidence appear to have been vascular. 



Fig. 12. Ptilophyton Thomsoni, Daws. The lower 

 part of a main axis from the Upper Old Red of 

 Scotland. After Salter (1859). 



