CH. IV] PROCORMOPHYTES 47 



propose to place them in a new class "the Psilophytalesi," 

 "characterised by the sporangia being borne at the ends of 

 certain branches of the stem without any relation to leaves or 

 leaf-like organs^." Among existing Pteridophyta the authors 

 find in the living genera of the Psilotales the closest parallel to 

 Psilophyton. 



These conclusions, however, should not be accepted without 

 some reservation. For our part we find ourselves unable to 

 adopt them, for it ajDpears to us that Psilophyton has been 

 misinterpreted and that this and all the other genera belonging 

 to what has here been called the Psilophyton flora were much 

 more probably Thallophyta than Pteridophyta. This however is 

 likely to be a matter of prolonged controversy, involving a dis- 

 cussion of what we mean exactly by the former term. 



In using this term here we recognise that the real problem is— - 

 was Psilophyton simply a Thallophyte or was it a very reduced 

 Pteridophyte ? In supporting the former view, as opposed to 

 recent workers on these fossils, we do not urge that, because this 

 or other genera were Thallophytes, they were necessarily Algae 

 in the sense in which that group is usually defined from a know- 

 ledge of its living members. On the contrary we think that 

 Psilophyton and some though perhaps not all the other genera, 

 belonged to a now obsolete race of Thallophyta, higher in the 

 scale of complexity than any living Algae. These plants we 

 propose to term the Procormophytes, and they will be further 

 discussed in a later chapter (p. 70). 



Several members of the Psilophyton flora appear to have been 

 Algae pure and simple. This is the case with Taeniocrada 

 according to White ^ and Parka according to Don and Hickling*. 

 On the other hand in Psilophyton, Arthrostigma and Pseudo- 

 sporochnus, we meet with other genera which appear to occupy 

 a somewhat higher position in the scale of morphological com- 



1 This term is open to considerable objections on the grounds that it is 

 too similar in form to another already in general use, i.e. the Psilotales. 

 If it is maintained, confusion is certain to arise from the similarity between 

 these names. 



2 Kidston and Lang (1917), p. 779. 



3 White (1905). 



" Don and Hickling (1917). 



