Bower. — Studies in the Phytogeny of the Filicales. 445 
succession of sporangia in the sorus; also that the obliquity of the annulus 
is equally shared with Gleichenia , while in § Mertensia the form and size 
of the sporangium is not unlike that of Plagiogyria ; it differs, however, 
in the important features of the much larger spore-output, and the median 
dehiscence shown by Gleichenia. The comparison has also been instituted 
above with the sporangium of Anemia , to which the sporangium of Plagio¬ 
gyria shows similarity in the essentials of construction, and in the in¬ 
definiteness of the stomium ; but it differs in the important point of number 
of the spores produced ; in these respects there is perhaps a closer 
comparison with the condition seen in the Matonineae, where also there is an 
oblique annulus and lateral dehiscence, together with a small spore-output. 
These comparisons, all of which place Plagiogyria in relation with 
relatively primitive Ferns as regards the characters of the mature sporangium, 
raise also the comparison on the basis of segmentation of the young 
sporangium, as well as of the apices of the various parts (compare ‘ Land 
Flora, 5 p. 650). It has been seen above that the details of segmentation 
of the young sporangium conform to that type which appears in the more 
primitive Leptosporangiatae, such as the Cyatheaceae and Dicksonieae: 
also that the segmentation of the apices is according to that common to 
Leptosporangiatae at large, while in the segmentation of the wings of the 
leaf there is nothing to strengthen the comparison with the Osmundaceae, 
which therefore rests rather on external features than upon internal 
structure or details of development. This is in fact the position which 
might have been anticipated. 
In this place it is only right to express the regret that the prothalli 
available for study have been open to some doubt as to identity. Pending 
the clearing up of this uncertainty it may be remarked that the antheridia 
observed showed dehiscence of the type characteristic of the more advanced 
Leptosporangiate Ferns ; but in view of the uncertainty that exists it is 
unavoidable that our comparisons shall at present be confined to the 
sporophyte generation, and any conclusions must in so far be held to be 
provisional, pending the facts relating to the sexual generation. 
But, subject to this proviso, the facts relating to the sporophyte are 
distinctive, and they indicate clearly that the affinities of the genus are 
relatively primitive ; this follows from (1) the entire absence of flattened 
scales, the young parts being protected by filamentous hairs only ; (2) the 
occasional dichotomy of the shoot; (3) the simple venation of the leaves, 
with absence of connecting commissures ; (4) the stelar structure, not far 
removed from solenostely ; (5) the undivided leaf-trace ; (6) the absence of 
a 'true 5 indusium, the sori being covered by the recurved leaf-margin; 
(7) the type of sorus with initially simultaneous sporangia, among which others 
are intercalated later; (8) the structure of the sporangium with oblique 
annulus and indeterminate stomium ; (9) its mode of initial segmentation 
