230 Arber . — On the Past History of the Ferns . 
figure in the case of the Eusporangiatae or of the Hydropterideae, such as 
would indicate a period or periods when these plants were in the position 
of dominant groups, is remarkable. The broken lines, in these and other 
cases, imply that the present evidence for the existence of such groups in 
certain geological periods is not entirely satisfactory. 
As is already generally agreed, the Leptosporangiatae were, in the 
Mesozoic period, in the position of a dominant group, and most of the 
families still existing had then become differentiated. 
But in the Palaeozoic period it seems doubtful if we can distinguish 
clearly between two groups, the Eusporangiate and the Leptosporangiate. 
It is more probable that the members of the Fern alliance, which then 
existed, although not in the later Palaeozoic forming a dominant group, 
were really an ancient stock, from which the Mesozoic Leptosporangiatae 
were derived. For this ancient group, the name Primofilices is suggested, 
and the Botryopterideae are regarded as being the, at present, best-known 
family within that group. 
As the result of recent research on the nature of the male and female 
organs of the Cycadofilices, which has tended to show that many of the 
Fern-like fructifications occurring in the Palaeozoic rocks, formerly regarded 
as belonging to Eusporangiate Ferns, are more probably the male organs 
of Pteridosperms, it can no longer be held that the Eusporangiatae were 
a dominant group in Palaeozoic times. Thus the Geological Record no 
longer supports the conclusion arrived at by some botanists from a study 
of the recent Ferns, that the Eusporangiate is the more primitive type as 
compared with the Leptosporangiate. 
The life-line of the Eusporangiatae can only be regarded at present as 
obscure, so far as the Palaeozoic and Mesozoic rocks are concerned. Even 
in the latter, little evidence of this race is to be found. Certain fronds of 
Taeniopteris are perhaps the best examples which have been put forward 
in this connexion, but even this genus is not entirely above suspicion. As 
regards the Palaeozoic fructifications, formerly regarded as belonging to 
Eusporangiate Ferns, it is impossible to say at present, which were really 
of this nature, and which were the male organs of Pteridosperms. Until 
this can be decided, at least in some degree, it will be impossible to trace 
back the life-line of the Eusporangiatae with any confidence. 
It is pointed out that the male organs of Pteridosperms and the 
Bennettiteae present a remarkable case of homoeomorphy when compared 
with the isosporous fructifications of the modern Eusporangiatae. The 
precise significance of this phenomenon is no doubt a matter of opinion, 
but it is pointed out here that it may be simply due to parallelism of 
development. 
As regards the Hydropterideae, there are no real grounds for believing, 
so far as the present evidence is concerned, that they existed at all in the 
