no Bower . — Is Eusporangiate or Leptosporangiate 
comes more complex, the identity of the single initial is lost, 
and the regular sequence of segmentations gives place to 
a less definite arrangement. On these characters therefore, as 
well as on these of the mature parts to which the meristems 
give rise, the Ferns may be arranged as a series : at the one 
end are the typically more delicate Leptosporangiate Ferns, 
while at the other would be the typically more robust Eu- 
sporangiate forms. It was further remarked in the paper 
above quoted that this parallelism as regards complexity of 
structure does not appear only in the parts of the sporophyte, 
but also that it may be traced in the sexual generation : that 
in the Hymenophyllaceae, which have a peculiarly delicate 
structure of the sporophyte, the prothallus is frequently fila- 
mentous, and the* sexual organs freely exposed, while in the 
more robust Eusporangiate Ferns, such as Marattia or Ophio - 
glossum , the prothallus is massive, and the sexual organs 
deeply sunk in its tissue. Accordingly, whether the general 
character of the sporophyte, or of the gametophyte be con- 
sidered, the divisions of the Filicineae might be arranged as a 
series, extending from the typically Leptosporangiate forms 
on the one hand to the typically Eusporangiate on the other ; 
the Osmundaceae, and in some respects the Schizaeaceae, also 
taking an intermediate position, and serving as connecting 
links between the two extremes. The question whether or 
not this series is to be regarded as a simple linear sequence, 
will be discussed later on. 
The series thus roughly blocked out appears to be a natural 
one, from the facts that the Filicineae themselves are obviously 
a natural group, and that the steps from one extreme to the 
other are gradual and consistent in all the parts. The next 
question will naturally be, which is the lower and which the 
upper end of the series ; which is the more primitive, and 
which the more recent, and derivative type ? It is to the re- 
consideration of this very important question that I propose 
to devote the following pages. The opinion currently held by 
botanists is that the simpler, Leptosporangiate Ferns are the 
more primitive, and that the Eusporangiate Ferns occupy 
