574 FILICALES 
These features indicate that Zoxsoma is more nearly related anatomically 
to the Dicksonieae and Dennstaedtiinae than to any other family of 
Ferns; but a reasonable analogy is also to be found with the more 
advanced species of Gleichenia: the solenostelic structure seen in G. 
, pectinata as well as the origin of its foliar trace are points for comparison, 
while structural affinities of a more remote nature are also indicated with 
the Schizaeaceae and Hymenophyllaceae. 
It thus appears that Zoxsoma is a generalised type, while its rare 
and local occurrence countenances this view. In habit it shows similarity 
to such genera as Dennstaedtia, Muicrolepia, and Davallia, a comparison 
which finds support in the anatomy of the vascular system: not only do 
the habit and anatomy support this, but also the form of indusium and 
receptacle, and the basipetal succession and orientation of the sporangia. 
An affinity with the Hymenophyllaceae is also unmistakable, but probably 
not so close as has often been assumed: against it are the texture of the 
leaf, the mode of dehiscence and the structure of the sporangium, 
and the low output of the very large spores: in any case the affinity 
is with the less specialised types (e.g. Hymenophyllum dilatatum) rather 
than the more specialised (eg. Zichomanes). The sporangium, and its 
annulus and dehiscence point clearly towards the Gleicheniaceae and 
Schizaeaceae; and though the habit of the leaf is different from these 
Ferns, the structure of the creeping rhizome shows a certain resemblance. 
The similarity of position of the annulus, and constancy of orientation 
are important, especially when taken with the very peculiar facts of induration. 
For, as we have seen, the distal side of the annulus is indurated, while 
the proximal can still be followed, though it is commonly thin-walled ; 
but occasionally single cells, or groups of cells, of the proximal side are- 
also indurated: these c&nnot be functionally active, since they do not 
form a connected series. In them I think we can only see a decadent 
vestige of a completely indurated annulus, and conclude that Zoxsoma was. 
derived from ancestors with a complete oblique annulus, probably with 
a median dehiscence. Such ancestry might be found in the neighbourhood 
of Glechenta. In Gil. dichotoma we have a type in which the sporangium 
and the sorus are similar in their main character. If we imagine these 
sori to be marginal (as they are in Lygodéum), surrounded by a cup-like 
annulus which is already suggested in some Gleichenias, with the annulus. 
modified as explained above to suit the more crowded sorus, and with a 
smaller number of spores, balanced by a larger number of sporangia 
produced in basipetal order, the sorus of Zoxsoma would be before us. It 
is not suggested that any living Gleichenia was a progenitor of Loxsoma, 
but Loxsoma appears to be a link connecting the Glecchenta Schizaea 
affinity with the type of Dennstaedtia and Microlepia. It should be 
regarded as the sole representative of a distinct tribe: the attempt should 
not be made to force it into any other tribe of living Ferns. 
