229 
Arber . — On the Past History of the Ferns . 
fossil must be considered for the present as 4 not proven.’ At any rate, we 
have better grounds for regarding Sagenopteris as possibly a member of 
the Hydropterideae, than in the case of any fossil known to us from 
the Palaeozoic rocks. 
We see, therefore, that the Geological Record does not support the idea 
that the Heterosporous Ferns were, in any sense, an ancient race. On the 
present evidence, I am inclined to think that they branched off from the 
Homosporous Ferns, in all probability from the Leptosporangiate line of 
descent, during the Mesozoic period, with specialization to a hydrophilous 
habitat. As a concession to the necessities of their new environment they 
have evolved heterospory, but not that particular type of heterospory 
which we associate with a seed. In these Ferns we have a new line of 
development, a distinct type of heterospory, and one which, so far as I am 
aware, is a much more modern contrivance, in a geological sense, than the 
seed. 
General Conclusions. 
The main results which have been arrived at here are expressed dia- 
grammatically in Figure i. The form of the life-line of the Leptosporan- 
giatae is interesting in comparison with that of the Cycadophyta, which 
is also shown in the diagram. The absence of any broadening of the life- 
Cycado- Cycado- Primo- Lepto- Hydro- Eusporan- 
phyta Alices Alices sporangiatae pterideae giatae 
Fig. t. A diagrammatic representation of the Life-lines of the Ferns and certain other groups, 
showing the geological periods at which some of them attained to the position of dominant 
factors in the vegetation. 
