394 Bower.— Studies in the Phytogeny of the Filicales . 
may be anticipated. The more perfect ‘ Acrostichoid ’ condition has been seen 
in B. alpinum , and a commissure was there present, at least in most cases. 
Moreover, a flange is clearly seen there. But in B. filiforme, which is nearer 
to Stenochlaena in habit, the marginal flange was variable, and apt to be 
reduced to vestigial proportions. This suggested an examination of Steno- 
chlaena in this respect. It was found that frequently there is virtually no 
sign of a flange (Fig. 17, c), or only a very slight waviness of the outline of 
the section (Fig. 17, a, b). In other cases the irregularity of outline was 
more marked (Fig. 17, e), while occasionally a slight flange, even with 
characteristic segmentations, maybe seen (Fig. 17, /). Such conditions, 
inconstant though they are, when taken together with the facts of anatomy 
and of external form, support the hypothesis that Stenochlaena is really 
a Blechnoid type, of origin from some forms like alpinum and filiforme ; 
that it has assumed a climbing habit as prefigured by B. filiforme , with 
peculiar differentiation of the sterile leaves. The structure of its fertile pinnae 
appears simple ; possibly it was primitively so, but more probably it came 
about by obliteration of the flange ; there was also a spread of its soral 
area, so as not only to merge the sori into a continuous band, but also 
to spread it into a wide ‘ Acrostichoid ’ surface. But the commissure was 
either non-existent from the first, or it became obliterated. 
We thus arrive at an ‘Acrostichoid’ type as derived from a Blechnoid, 
and ultimately from a probable Matteuccoid source. It may be a question 
whether similar lines of progression may not account for other ‘Acrostichoid’ 
types, which have gone under the names of Lomariopsis and Polybotrya. 
But such questions must be left open for further study. 
As the sporangia of Stenochlae?ia appear to be fair examples of those 
of the Blechnoid affinity, they have been examined carefully, and illustrated 
by drawings (Text-fig. 12, a-d ). Their structure seems to be rather 
variable, and in size and number of the cells of the annulus they fall short 
of Matteuccia (compare Text-fig. 2). But at least in the great majority of 
cases the annulus appears to be interrupted at the stalk. A close examina- 
tion shows an intermediate state between the oblique continuous annulus 
and the vertical and interrupted ; this has been observed elsewhere in forms 
which on other grounds have been held as transitional (cf. Dennstaedtia 
apiifolia , Phil. Trans., vol. 192, p. 73, and Fig. 131). In the present case the 
point of interest lies in the detail of the insertion of the stalk in its relation 
to the annulus. Text-fig: 12, a, , shows a sporangium seen from the side. 
Immediately below the capsule the stalk consists of three rows of cells, though 
lower down it may be more complex. Of these, two rows are continuous 
up to that face of the sporangium which corresponds to the ‘ central ’ face of 
the Gleicheniaceous or Cyatheaceous type (see Land Flora, p. 556). The 
third row, marked x , runs up to the face corresponding to that described 
as ‘peripheral’ in the sporangia of those Ferns. Text-fig. 12, d, shows 
