446 Bower. — Studies in the Phytogeny of the Filicales. 
leading to a relatively thick stalk; (io) the tetrahedral form of the spores. 
All these characters indicate for the genus a relatively primitive position, 
and the strength of that conclusion lies in the number of the facts upon 
which it is based. 
From the comparisons detailed in the above pages it will be apparent 
that Plagiogyria does not naturally fall into any of the families of Ferns 
which have an oblique annulus ; it is a type of which the cross characters 
indicate some intermediate position, with affinities in various directions ; 
in fact it is a ‘ synthetic ’ type. But though the bulk of the indications are 
clearly towards the Simplices, they do not relate the genus specially with 
any family of them ; thus the habit suggests the Osmundaceae, the anatomy 
the Schizaeaceae, and the sorus the Gleicheniaceae or Matonineae, while 
the venation would compare reasonably with any of these. But it is plainly 
a primitive type which has broken away from its original characters, as is 
seen in the dictyostelic structure of the mature stem following on solenostely 
and even protostely, and in the mixed character of the sorus. It would 
seem probable that the mixed character of the sorus was acquired directly 
from the simple state ; from the entire absence of any indication of basipetal 
sequence of the sporangia it is probable that this took place without the 
intervention of any gradate condition, as in the case of the Dennstaedtia - 
Davallici series ; 1 it has here been achieved by the simple interpolation of 
new sporangia between those formed in the first instance. There is a 
precedent for this already recognized within the genus Dipteris ; for while 
in Dipteris Lobbiana the sori show simultaneous origin of the sporangia, 
D. conjugata , which on other grounds may be held to be a more advanced 
type, has a mixed character of the sorus. It was concluded in that case 
that a direct progression had been effected from the simple to the mixed 
condition of the sorus within the limits of a very natural genus; and the 
conclusion appears probable that a like direct progression has produced 
what is seen in the sorus of Plagiogyria ; this conclusion eliminates any 
near relationship with the Gradatae. 
In the dictyostelic structure of the axis, as well as in the mixed sorus, 
Plagiogyria compares with the Mixtae, and especially, as indicated by the 
characters of position and protection of the sorus, with that relatively 
primitive group of them, the Pterideae; but it differs from them in its 
oblique annulus; the question will therefore be whether in any of the 
Pterideae there is indication of a like feature. Without entering here into 
details, which must be reserved for a future paper of this series, it may be 
stated that there is evidence among the Pterideae of the existence of an 
oblique annulus, and that it is found in the genus Cryptogramme , which has 
already been placed by Diels in near systematic relation to Plagiogyria. 2 
1 See Studies in the Morphology of Spore-producing Members. IV. Leptosporangiate Ferns. 
Phil. Trans., B., vol. 192, p. 91. 2 Engler and Prantl, i, 4, pp. 279-81. 
