588 FILICALES 



Hymenophyllum yield 128 as the typical number. These are figures which 

 find no correlative in ordinary Leptosporangiate Ferns, but only among 

 the Simplices, a fact which strongly supports the view above expressed. 

 On the other hand, certain species of Trichomanes show only low spore- 

 output, but they are on other grounds regarded as specialised, and their 

 small sporangia and low output are further indications of their derivative 

 character. 



It would be impossible to close any comparative account of the Hymeno- 

 phyllaceae without some reference to the gametophyte, for it has figured 

 largely in previous discussions. Trichomanes is the simpler type of the 

 family in its prothallus : while that of Hymenophyllum consists of a broad 

 ribbon-like expansion, that of Trichomanes is usually filamentous, with more 

 massive archegoniophores. The archegonia of these Ferns do not show 

 distinctive features, but Heim, 1 who has drawn attention to the value 

 of antheridia for comparative purposes, specially notes the similarity of 

 those of the Hymenophyllaceae to those of the Gleicheniaceae. This is 

 a fact of importance when taken with the data of spore-output, for 

 it is thus seen that features of the reproductive organs of both generations 

 indicate a similar affinity. 



The result of a general comparison of the Hymenophyllaceae with other 

 Ferns is then to recognise that they approach most nearly to certain of 

 the Simplices, with which they agree in many points, both of the sporophyte 

 and the gametophyte. The structural peculiarities of the gametophyte 

 apart from the sexual organs are probably in large measure the result of 

 secondary adaptation : a comparison of the antheridia, however, points to 

 certain of the Simplices. The characters of the sporophyte are more 

 distinctive : they point, in one feature or another, to all the known protostelic 

 families of the Simplices, but to no one family in particular : so that it is 

 impossible at present to locate the origin of the family with any degree 

 of exactitude. The Hymenophyllaceae are to be looked upon as of early 

 origin, but ending as a blind line of descent, characterised by specialisation 

 of both generations to a hygrophilous habitat, which has taken the form 

 of simplification ; in both generations Trichomanes shows the greater 

 simplicity, and is on that account to be held as more removed from the 

 original source. 



1 Flora, 1896. p. 363. 



