30 Bonier. — Studies in the Phytogeny of the Filicales . VI. 
in a manner to give general satisfaction. Indeed the passages from one to 
another group or genus are too apparent to escape notice, and I have 
thought it better, with the single exception of Platycerium , to consider the 
groups of sectional than of generic value.’ Nevertheless his subdivision of 
the genus into numerous sub-genera shows his clear realization of the hetero- 
geneity of the Ferns included. Naturally his method was pre-evolutionary. 
His object in adopting an extended limit of the genus was perfectly logical 
according to the views of the time and the limited facts which he possessed. 
To him species were definite units. His object was to group these units 
according to characters readily grasped. In vol. i, p. 3 of the ‘ Species 
Filicum ’ he explains that the main object of the work is £ to assist the tyro in 
the verification of genera and species From this point of view the exten- 
sion of the generic conception was justifiable. Nor ought we to denounce 
as unscientific a method so direct and consequent as this because the premise 
of immutability of species, generally held at the time, underlies it. None 
the less, the method and the conclusions fall away so soon as the premise 
itself breaks down. Our duty is then to substitute some phyletic grouping 
in accord with the current belief in mutability and progression. This may 
be done by comparison along lines of as many characters as possible. 
These will, however, be very largely those of the sporophyte. For not only 
are the gametophyte characters in many cases insufficiently known, but also 
such characters are apt to be less conclusive than those of the sporophyte. 
Proceeding on such lines it has already been shown by various writers 
that Ferns of Acrostichoid character are referable to types with distinct sori. 
Indeed the exaggerated genus of Hooker has been so whittled away that in 
Christensen’s Index only three names remain. All the rest are now referred 
to other genera. The attempt may now be made to summarize those 
references with a view to realizing how widespread has been the origin 
of the Acrostichoid character. 
The sub-genera included under Acrostichum in the ‘ Synopsis Filicum ’ 
are as follows, while noted after each is its designation according to 
Christensen’s Index: 
Elaphoglossum — a substantive genus retaining its name. 
Stenochloena — a substantive genus retaining its name. 
Polybotrya — a substantive genus retaining its name. 
Egenolfia — included in Polybotrya. 
Rhipidopteris — included in Elaphoglossum. 
Aconiopteris — included in Elaphoglossum. 
Stenosemia — a substantive genus retaining its name. 
Soromanes - — referred to Polybotrya. 
Gymnopteris — included in Leptochilus . 
Chry sodium — the species all referred to other genera, and the genus 
is thus sunk. Part of it constitutes the surviving genus Acrostichum. 
