PRESIDENTIAL ADDRESS. 569 
becomes possible upon the sum of them to lay out tle species and genera of Ferns 
themselves in series, from the primitive to the advanced. In proportion as the 
progressions on the basis of the several criteria run parallel, we derive increased 
assurance of the rectitude of the phyletic sequences thus traced, which may finally 
be clinched, as opportunity offers, by reference to the stratigraphical occurrence 
of the corresponding fossils. This is in brief the phyletic method, as it may be 
applied to Ferns. It may with suitable variation be applied to any large group of 
organisms, though it is seldom that the opportunities for such observation and 
argument are in any sense commensurate with the requirements. Perhaps there 
is no group of plants in which the opportunities are at the moment so great as in 
the Filicales, and they are yielding highly probable results from its application, 
The greatest obstacle to success is found in the prevalence of parallel develop- 
ment in phyla which are believed to have been of distinct origin. This is 
exemplified very freely in the Ferns, and the systematist has frequently been 
taken in by the resemblances which result from it. He has grouped the plants 
which show certain common characters together as members of a single genus. 
Sir William Hooker in doing this merged many genera of earlier writers. His 
avowed object was not so much to secure natural affinitv in his system as readiness 
of identification : and consequently in the ‘Synopsis bilicum ’ there are nominal 
genera which are not genera in the phyletic sense at all. For instance, Poly- 
podium and Acrostichum, as there defined, may be held from a phyletic point of 
view to be collective groupings of all such Ferns as have attained a certain state 
of development of their sorus; and that they are not true genera in the sense of 
being associated by any kinship of descent: this is shown by the collective 
characters of the plants as a whole. Already at least four different phyletic 
sources of the Acrostichoid condition have been recognised, and probably the 
sources of the Polypodioid condition are no fewer. Such ‘genera’ represent the 
results of a phyletic drift, which may have affected similarly a plurality of lines 
of descent. It will be the province of the systematist who aims at a true group- 
ing according to descent to comb out these aggregations of species into their 
true relationships. This is to be done by the use of wider, and it may be quite 
new, criteria of comparison. Advances are being made in this direction, but we 
are only as yet at the beginning of the construction of a true phyletic grouping of 
the Filicales. The more primitive lines are becoming clearer: but the difficulty 
will be greatest with the distal branches of the tree. For these represent 
essentially the modern forms, they comprise the largest number of apparently 
similar species, and in them parallel development has been most prevalent. 
If this difficulty be found in such a group as the Filicales, in which the earlier 
steps are so clearly indicated by the related fossils, what are we to say for the 
Angiosperms? Our knowledge of their fossil progenitors is very fragmentary. 
But they are represented now by a multitude of forms, showing in most of their 
features an irritating sameness. For instance, vascular anatomy, that great 
resource of phyletic study in the more primitive types, has sunk in the Angio- 
sperms to something like a dead level of uniformity. There is little variety 
found in the contents of embryo-sacs, in the details of fertilisation, or in 
embryology. Even the ontogeny as shown in the seedling stages affords little 
consolation to the seeker after recapitulation. On the other hand, within what 
are clearly natural circles of affinity there is evidence of an extraordinary readi- 
ness of adaptability in form and structure. Such conditions suggest that we see 
on the one hand the far-reaching results of parallel development, and on the other 
the effects of great plasticity at the present day, or in relatively recent times. 
Both of these are points which prevent the ready tracing of phyletic lines. In 
the absence of reliable suggestions from paleontology, the natural consequence is 
the current state of uncertainty as to the phyletic relations of the Angiosperms. 
Various attempts have been or are being made to meet the difficulty. Some, 
on the basis of the recent observations of Wieland and others, are attempting 
along more or less definite monophyletic lines to construct, rather by forcible 
deduction than by any scientific method of induction, an evolutionary story of the 
Angiosperms. I do not anticipate that any great measure of success, beyond 
what is shown in a very polysyllabic terminology, and an appearance of knowing 
more than the facts can quite justify, will attend such efforts. It would seem 
to me to be more in accord with the dictates of true science to proceed in a 
different way, as indeed many workers have already been doing. To start not 
