HOOKER LECTURE, 1917. 121 
the Oak and Beech Ferns, or Polybotrya osmundacea. A side branch 
from Matteuccia led to Blechnum, with Scolopendrium and Asplenium as 
further derivatives : also to Acrostichoid types, such as Stenochlaena and 
Brainea. A second related sequence starting from Matonia, led through 
Dipterid types to the Acrostichoid state of Cheiropleuria, Gymnopteris, 
and Platycerium. A third line is indicated by Metaxya and Syngramme, 
leading to the Acrostichoid genus Elaphoglossum. 
On the other hand, from the Schizæaceæ, which are the most important 
central stock of the living Marginales, we may trace the Dicksonioid- 
Davallioid Series, culminating in Polypodioid forms, such as P. punctatum. 
A side branch indicated by Lindsaya, Pæsia, and Pteris, culminates in 
Acrostichum aureum ; while a collateral line , probably leads from Mohria 
and Cheilanthes to such types as Hemionitis, and to the fully Acrostichoid 
state of Z'rismeria. 
From such seriations the fact of parallel development, or Homoplasy, 
as it has been well designated in one of the earliest papers of Lankester, 
emerges clearly. It is seen not in one case, nor yet in a single feature, 
but in many. A few examples may be quoted. The dendroid habit is 
characteristic of the Cyatheacez and the Dicksonies, two families which 
were merged by earlier writers, chiefly on the ground of habit. Both have 
sprung from a creeping ancestry. But the Cyatheacem have superficial 
sori and chaffy scales; the Dicksonieæ have marginal sori and dermal hairs. 
They represent distinct phyletie lines, the former being of Gleichenioid 
origin, the latter of Schizewoid descent. Yet they appear so similar in 
habit that detailed examination is necessary to distinguish them. They 
exemplify a parallel or homoplastie origin of the dendroid state. Again, 
dermal appendages illustrate in many distinct sequences the progression 
from simple hairs which are primitive, to scales which are advanced. The 
anatomical progression from protostely, to solenostely and dietyostely, as 
also to polycycly, is illustrated in a plurality of lines phyletically distinct. 
Soral characters show parallel progressions in many ways. The origin of 
the gradate and mixed conditions of the sori: the progressive reduction 
of the spore-output: the swinging of the oblique annulus to the vertical 
position: the change from median to lateral dehiscence: the protection 
of the sorus by those heterogeneous growths called indusia, of which there 
are some half-dozen distinct types: the loss of such indusia, giving the 
“ Polypodioid ” state: the spread of the sori to give the “ Acrostichoid ” 
condition :—these and many other progressive changes can be shown to 
have originated along a plurality of phyletic lines ; and they have resulted 
in some cases in so high a degree of similarity that the segregation of the 
forms showing them according to descent is difficult, however certain it may 
actually be. 
Thus the faet becomes clear as we proceed along the lines of phyletic 
progress demonstrated by the comparative study of the Filicales, that 
d. 
