Bower.—Studies in the Phytogeny of the Filicates. 447 
But the position of the annulus in Cryptogramme is more nearly vertical, 
and its induration is interrupted opposite the insertion of the stalk; these 
are steps which lead towards the condition of the annulus common in Ferns 
with a mixed sorus, and seen in other Pterideae. Such facts indicate the 
correctness of the conclusion that Plagiogyria , though independent of near 
relation to any of the families of the Simplices, is a form which has broken 
away from the primitive state in certain features, and that, as a synthetic 
type, it serves as an indication of the probable origin of those features 
which characterize a certain group of the Mixtae, viz. the Pterideae, to 
which it has already been held by systematists to be akin. 
The attempt must now be made to locate this synthetic type, Plagio¬ 
gyria , in the system of the Filicales. In the first place the generic 
separation of it from Lomaria cannot be for a moment in doubt; Plagio¬ 
gyria must certainly be held to be a substantive genus ; the question will 
be whether a higher degree of systematic separation is not required for 
a form which combines such distinct features. It might at first sight seem 
desirable to found a new order of Ferns to accommodate it; and my first 
impulse was to establish it as the only genus of a new order, the Plagio- 
gyriaceae. But reflection upon the facts which point to its natural alliance 
with the simpler Pterideae, and especially the fact that traces of an oblique 
annulus exist in Cryptogramme , indicates that a separation is not desirable. 
A natural order should be as nearly as possible a phyletic unity. Our 
conclusion from the comparison of the facts must be that Plagiogyria gives 
the key to certain changes which have accrued in the descent of the 
Pterideae, such as the progression anatomically towards the dictyostelic 
state though maintaining the united leaf-trace, and the progression from 
the simple to the mixed sorus with the swinging of the oblique annulus 
to the vertical position, together with its interruption at the insertion of the 
stalk. If, within the Pterideae, there were no forms which shared in any 
degree the peculiar characters of Plagiogyria , then a separate systematic 
position might be desirable for the genus. But as it now appears that 
anatomically, as well as in the characters of the annulus, it does not stand 
entirely apart, the conclusion seems justified that its natural place is 
within the Pterideae. But of these it must be ranked as the most primitive 
form, while its affinity in character with the various groups of the 
Simplices, but not especially with any one of them, indicates a probability 
that the Pterideae sprang directly from such a source, though not from any 
one of the families of them at present known. Accordingly no change 
from the definition of the sub-families or of genera of the Pterideae as 
arranged by Diels 1 is proposed as a consequence of the new facts ; but as 
regards phyletic grouping, which will be worked into further detail in 
subsequent papers of this series, Plagiogyria will be placed in the lowest 
1 1. c., p. 255. 
