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 Z7richomanes 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. Z7yichomanes is the simpler type of the 
family in its prothallus: while that of Hymenophyllum consists of a broad 
ribbon-like expansion, that of Zrichomanes is usually filamentous, with more 
massive archegoniophores. The archegonia of these Ferns do not show 
distinctive features, but Heim,! 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 TZ?7ichomanes shows the greater 
simplicity, and is on that account to be held as more removed from the 
original source. 
1 Flora, 1896, p. 363. 
