iiij THURSOPHYTON 29 



cular tissue forming a solid column without any pith. This 

 much can be made out by macerating impressions. 



Petrifactions of this genus are as yet unknown, nor do we 

 know anything of its fructifications. 



We think it probable however that Arthrostigma and Psilo- 

 phyton are nearly related genera. 



Thursophyton. 

 (Figs. 10, 11.) 



Thursophyton, Nathorst^, 1915. Axes possibly herbaceous, 

 dichotomously branched, of uniform thickness. Axes covered 

 with crowded, imbricated, small (about 7 mm. long) scale-like 

 emergences, spirally arranged and lanceolate in form, swollen 

 at base, curving upwards. No leaf scars occur on thti stem. 

 Fertile shoots similar to the sterile axes bearing large (?) sporangia 

 in the axils of some of the scale-like emergences. 



Distribution. Upper Old Red, Scotland; Middle Devonian, 

 Bohemia, Western Norway. 



This fossil was originally described under the name Lycopodites 

 Milleri, Salter, but, as Nathorst has pointed out, it has little or 

 nothing in common with the Carboniferous plants referred to 

 that genus and it is therefore best transferred to a new genus, 

 Thursophyton. The first fertile shoots were described by Pen- 

 hallow- and later by Rcid and Macnair^ as a distinct species 

 T. Reidi, Penh. (Fig. 11, 1, p. 30). Here what appear to be 

 globular sporangia, 1 mm. in diameter, frequently occur in the 

 axils of some of the scale-like emergences. Nathorst^, who has not 

 seen actual specimens of these fertile shoots, regards Penhallow's 

 interpretation of these fossils as fertile as being extremely 

 doubtful. He suggests that it is not yet proved that the organs 

 in question are sporangia and that they might be foreign bodies. 

 While admitting the Justice of some doubt on these points and 

 the need of further evidence, we are inclined to think that 

 Penhallow's interpretation will eventually prove to be in the 

 main correct. For in the case of another species of the same genus, 



1 Nathorst (1915), p. 17. ^ Penhallow (1892). 



3 Reid and Macnair (1896). * Nathorst (1915), p. 19 footnote. 



