CHAPTER XXXI. 



COMPARATIVE DISCUSSION AND SUMMARY FOR THE 



OPHIOGLOSSALES. 



THE Adder's Tongues cannot yet be considered as located in a definite 

 position in relation to other groups of Pteridophytes. Their traditional 

 place among the Ferns was accorded to them somewhat light-heartedly, and 

 before the details of their anatomy or development were adequately known. 

 They share two external characters with the Ferns, viz. that they are large- 

 leaved, and that the sporangia are distributed over a considerable extent 

 of the foliar organ. But to use these in themselves as a ground for ranking 

 them as Ferns involves the assumption that the origin of a large sporophyll 

 only occurred once in Descent, an assumption that is not warranted. On 

 the other hand, a relationship with the Lycopodiales has been ascribed to 

 them : this has been based in the first instance upon the position of their 

 peculiar spore-bearing member, the spike, as it is called; and it has been 

 urged that the insertion of this part is the same as that of the sporangium 

 of the Lycopodiales or of the sporangiophore of the Psilotaceae, while the 

 function of these parts is also alike. This argument, like the first, draws 

 its cogency from an assumption, that all the appendages holding a ventral 

 position on the leaf were of common origin. But parallel development in 

 distinct phyletic lines may account for this common feature, as it does 

 for so many others in the plant-body. The day is past when single 

 characters such as these can be accepted as defining relationships, and it 

 is in the study of all the characters that an indication of the natural 

 position of any family is to be found. Certain recent writers have indicated 

 a specially primitive position for the Ophioglossaceae, comparing them directly 

 with the Anthocerotales, 1 while V. Wettstein- gives them the first position 

 in his treatment of the Pteridophyta, with the remark that "the Ophio- 

 glossales are the only living Pteridophytes from which the rest of the 

 Pteridophytes can be derived." \Vith such divrrgrnt opinions before us 



1 Campbell, Mosses and /v;y/.r, 1905, p. 600. 

 - Handlntt'h <l. Syst. Bot., p. 52, etc. 



