THE BRIAN OB DEVONIAN FORESTS. 



67 



scales are rudimentary. They also bear some resemblance, 

 though on a much larger scale, to the spore-cases of some 

 Erian ferns {Arclimopteris), to be mentioned in the 

 sequel. On the whole, however, they seem most nearly 

 related to the sporocarps of the Rhizocarpea3. 



Arthrostigma, which is found in the same beds with 

 Psilophyton, was a plant of more robust growth, with 

 better-developed, narrow, and pointed leaves, borne in a 

 verticillate or spiral manner, and bearing at the ends of 

 its branches spikes of naked sporocarps, apparently simi- 

 lar to those of Psilophyton but more rounded in form. 

 The two genera must nave been nearly related, and the 

 slender branchlets of Arthrostigma are, unless well pre- 

 served, scarcely distinguishable from the stems of Psilo- 

 phyton.* 



If, now, we compare the vegetation of these and simi- 

 lar ancient plants with that of modern Rhizocarps, we 

 shall find that the latter still present, though in a de- 

 pauperated and diminished fo^-m, some of the character- 

 istics of their predecessors. Some, like Pilularia, have 

 simple linear leaves ; others, like Marsilea, have leaves in 

 verticils and cuneate in form ; while others, like Azolla 

 and Salvinia, have frondose leaves, more or less pinnate 

 in their arrangement. The first type presents little that 

 is characteristic, but there are in the Erian sandstones 

 and shales great quantities of filamentous and linear ob- 

 jects which it has been impossible to refer to any genus, 

 and which might have belonged to plants of the type of 

 Pilularia. It is quite possible, also, that such plants as 

 Psilophyton glabrum and Cordaitcs angustifolia, of which 

 the fructification is quite unknown, may have been allied 

 to Rhizocarps. With regard to the verticillate type, we 

 are at once reminded of Sphenophyllum (Fig. 20), which 



* Reports of the auther on " Devonian Plants," " Geological Survey cf 

 Canada," which see for details as to Erian Flora of northeaatern America. 



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