CHAPTER XIII. 



PSILOTALES. 



The two recent genera Psilotum and Tmesipteris are usually 

 spoken of as members of the family Psilotaceae which is 

 included as one of the subdivisions of the Lycopodiales. It is 

 probable, as Scott' first suggested, that these two plants are 

 more nearly allied than are any other existing types to the 

 Palaeozoic genus Sphenophyllum. 



We may give expression to the undoubted resemblances 

 between Tmesipteris and Psilotum and the Sphenophyllales by 

 including the recent genera as members of that group, originally 

 founded on the extinct genus Sphenophyllum; this is the 

 course adopted by Thomas'' and by Bower*: or we may 

 emphasise the fact that these two recent genera differ in 

 certain important respects from Lycopodium and Selaginella by 

 removing them to a separate group, the Psilotales. The latter 

 course is preferred on the ground that the inclusion of Psilotum. 

 and Tmesipteris in a group founded on an extinct and necessarily 

 imperfectly known type, is based on insufficient evidence and 

 carries with it an assumption of closer relationship than has 

 been satisfactorily established. 



The genus Tmesipteris (fig. 120, A) is represented by a 

 single species T. tannensis Bertr.* which usually occurs as an 

 epiphyte on the stems of tree-ferns in Australia, New Zealand, 

 and Polynesia. Psilotum, with two species P. triquetrum, 



1 Scott (00). 2 Thomas (02). ^ Bower (08) p. 398. 



* Dangeard (91) and Bertrand, C. B. (81) recognise other species of Tmesipteris, 

 but it is doubtful how far such differences as exist are worthy of specific 

 recognition. 



