28 



THE PSILOPHYTON FLORA 



[CH. 



Fig. 10. Thursophyton Milleri, (Salt.) 

 from the Middle Devonian of Western 

 Norway. Sterile axes with seale-like 

 emergences. After Nathorst (1915). 



1 Kidston (1893), p. 108. 



thick, short (rudimentary or 

 broken) distant leaves." The 

 leaves here are pyramidal and 

 thorn-like. 



With regard to the mor- 

 phology of these spine-like 

 processes, Kidston 1 has con- 

 cluded that these are not " the 

 bases of leaves, as has been 

 suggested, but are the leaves 

 themselves, though developed 

 in a very rudimentary form, 

 as in Psilophyton" 



Halle 2 says "the append- 

 ages of- these stems can hardly 

 be anything but leaves." To 

 this we may reply that, on 

 the present evidence, they 

 are quite as likely to be emer- 

 gences, especially in view of 

 the similar structures occur- 

 ring in certain species of 

 Psilophyton, to which we have 

 just drawn attention. On our 

 view the emergences of Ar- 

 throstigma and Psilophyton 

 differ chiefly in size and the 

 variation in this respect in 

 the former genus (which Halle 

 has pointed out), as we have 

 just said, is exactly what we 

 should expect to find in view 

 of the corresponding varia- 

 tion met with in Psilophyton 

 (see pp. 21 and 22). 



Halle also confirms Daw- 

 son's conclusion that the 

 stem was vascular, the vas- 



2 Halle (1916), p. 13. 



