LAUEENTIAN AND EARLY PALAEOZOIC. 25 



ever, to realise the idea of arboreal plants haying struct- 

 ures akin to those of thallophytes, but with seeds so 

 large and complex that they can scarcely be regarded as 

 mere spores. They should perhaps constitute a separate 

 class or order to which the name NematodendrecB may 

 be given, and of which Nematophyton will constitute one 

 genus and Aporoxylon of linger another.* 



Another question arises as to the possible relation of 

 these plants to other trees known by their external forms. 

 The Protostigma of Lesquereux has already been referred 

 to, and Claypole has described a tree from the Clinton 

 group of the United States, with large ovate leaf -bases, to 

 which he has given the name Olyptodendron.\ If the 

 markings on these plants are really leaf-bases, they can 

 scarcely have been connected with Nematophyton, because 

 that tree shows no such surface-markings, though, as we 

 have seen, it had bundles of tubes passing diagonally to 

 the surface. These plants were more probably trees vrith 

 an axis of barred vessels and thick, cellular bark, like the 

 Lepidodendron of later periods, to be noticed in the sequel. 

 Dr. Hicks has also described from the same series of beds 

 which afforded the fragments of Ifematophyton certain 

 carbonised dichotomous stems, which he has named Ber- 

 wynia. It is just possible that these plants may have 

 belonged to the IfematodendresB. The thick and dense 

 coaly matter which they show resembles the bark of these 

 trees, the longitudinal striation in some of them may 

 represent the fibrous structure, and the lateral projections 

 which have been compared to leaves or leaf-bases may 

 correspond with the superficial eminences of Nematophy- 

 ton, and the spirally arranged punctures which it shows 

 on its surface. In this case I should be disposed to re- 



*See report by the author on "Brian Flora of Canada," IS'Tl and 

 1882, for full description of these fossils. 

 f " American Journal of Science," 1878. 



