386 Bower . — The comparative examination of the 
eusporangiate Ferns ; and to strengthen the bond between 
them and the Marattiaceae. A reference to the table of 
meristems given above (p. 376) shows further that in these 
characters Todea stands nearer to the latter than Osmunda , 
and this conclusion is further borne out by the presence of 
the commissure at the base of the leaf. On the other hand, 
as regards the meristems, Marattia appears to be nearer to 
the Osmundaceae than is Angiopteris ; thus on the basis of the 
meristems the series of genera would be Osmunda , Todea , 
Marattia , Angiopteris. It is, however, to be noted that the 
coalescence of the sporangia is less complete in Angiopteris 
than in Marattia. 
It remains to remark on the probable relation of this Filici- 
neous series to other forms. There is, I think, every reason to 
believe that the Hymenophyllaceae are of Algal-Bryophytic 
origin, and they probably arose from some forms intermediate 
between our present green Algae and the Bryophyta, but not 
directly from either as we now see them ; the position of the 
Hydropterideae (the only heterosporous Ferns) is probably in 
relation rather to the lower terms of thehomosporous series than 
to the higher ones. Then, as regards the vegetative organs of 
the sporophyte, whether we take external form, internal struc- 
ture, or development into account, the relation of the highest 
Pteridophyta (Marattiaceae and Ophioglossaceae) to the Cyca- 
daceae is undeniable ; but between these, as regards reproduc- 
tion, there is the vital difference between the homosporous 
zooidogam and the heterosporous siphonogam. Though there 
is no reason to assume that progress in vegetative structure and 
in sexual differentiation has necessarily taken place simul- 
taneously, still, this is a very serious gap, and from the point 
of view of phylogeny it is very desirable to find some hetero- 
sporous form allied to the Marattiaceae, which should serve as 
a connecting link. Approaching the matter from the point of 
view of the characters of the leaf, I appended the following 
note to a paper written in 1884 1 : — ‘ The leaf of Isoetes 
shows intermediate characters between those of Angiopteris 
1 Phil. Tran. 1884, Part II, p. 610. 
