Bower. — Studies in the Phytogeny of the Filicates. 415 
Comparative Treatment and Phyletic Conclusions. 
In the above pages data are given relating to a very considerable series 
of Ferns which, both on the ground of old and persistent opinion of 
systematists, and on a basis of more recent and exact comparative study, arc 
believed to be naturally allied. The attempt must now be made to draw 
together these results with a view to phyletic conclusions. In a previous 
memoir of this series, numerous criteria have been cited which may be avail- 
able in Ferns for such an end (Ann. of Bot., vol. xxvi, p. 292, &c.). But it 
is not possible in every case to use all of the criteria there mentioned. 
Sometimes the facts themselves may be wanting, and that is so in regard 
to the whole gametophyte generation in many of the Ferns here examined. 
Again, when Ferns have progressed from a more primitive to a relatively 
advanced state, certain of the available criteria lose their validity, owing to 
the fact that all those types compared may have attained to a full state of 
development as regards that particular feature. For instance, advanced 
Ferns generally possess flattened scales ; therefore, in relatively advanced 
families the criterion of form of the dermal appendages loses much of its 
value, or all of it. In the present case such comparisons will take only 
a minor place. Again, in relatively advanced Ferns the usual vascular 
system of the axis is dictyostelic, with a divided leaf-trace. This is the case 
for virtually all of the Ferns here treated, and accordingly the vascular 
comparisons also lose much of their value. Further, in the more advanced 
Leptosporangiate Ferns the sporangium itself becomes very generally 
standardized ; that is, relatively uniform in size, structure, and spore 
number. This is so in most of the Ferns here considered, so that this 
criterion also becomes only of minor importance. The elimination of such 
useful criteria as these, or the diminution of their value, throws the weight 
of argument upon those that remain. In the present case, venation, the 
form and construction of the sorus, and of certain parts accessory to it, will 
have to bear the brunt of the comparative arguments, while external form, 
dermal appendages, and anatomy will also have to take their proper, though 
a minor, share in the comparisons. 
External Form. 
Throughout the Ferns of Blechnoid affinity there is some degree of 
inconstancy in the position of the axis, and in its proportion to the other 
parts of the shoot. In the case of the Onocleineae the genus Onoclea has 
an elongated creeping rhizome, whil e Matteuccia (Struthiogteris) has a com- 
pact and upright stock. But even in the latter case the upright stock is 
commonly preceded by an elongated, runner-like tract, in those cases where 
branching occurs in relation to the leaf-bases. This is well illustrated in 
M. germanica . A somewhat similar arrangement is seen also in Plagiogyria , 
