The Principles of Morphology. 169 
group 1 . It would almost seem preferable, therefore, to place them 
in a distinct phylum of their own ; yet in view of their evident close 
resemblance to certain of the Schizaeaceae, e.g. Aueiinia, I am rather 
disposed myself to regard them as Ferns of a very primitive and 
elementary type. It must always be remembered that this latter is 
a very vague term indeed ; that there are Ferns and Ferns ; and that 
it does not necessarily follow that, for instance, the Polypodiaceae are 
anything but very remotely allied to such a group as the Schizaeaceas, 
this latter standing nearer to the ancient generalised type as shewn 
both by its sporangial tissues and stem-anatomy, yet at present it 
appears to be following a -very “ Filicinean ” course of evolution ! 
So do the Ophioglossaceae, at any rate as regards the evolution of 
their foliar organs. 
The “primary sporangium,” a lateral repetition of the primitive 
sporogonium, constitutes then the matrix out of which all subsequent 
sporophylls, sporangiophores and sporangia have evolved. The 
terminal sporangium became divided into superior and inferior 
(adaxial and abaxial) portions. Sterilisation and sub-division of the 
former gave rise to the type found in the Sphenophyllales, 
Equisetales, Lycopods, Ophioglossaceae and Schizasaceae (at any rate 
Ancimia). The same process taking place in the inferior or abaxial 
sporangium probably gave rise to the complex assimilating and 
sporangiferous sporophylls of the typical Ferns. The sporangia at 
first were marginal structures, i.e. terminal to lateral segments of 
the leaf, e.g. Osmundaceae, Hymenophyllaceae, Schizaeaceae, 
Lyginodendron ; there subsequently arose a tendency for them to 
become displaced on to the lower surface of the sporophyll, as 
in Schizaeaceae, Polypodiaceae, male sporophylls of Coniferae, 
Cycadaceae. 
A curious equivalence, probably due to reduction of the 
sporophyll, is found between the “ primary sporangia ” or secondary 
sporogonia and the ovules of Gnetaceae and Coniferae; in these 
latter the entire leaf is the sporangium just as it was in the far-back 
primitive condition. 
1 The idea must not be entertained that the Ophioglossaceae have 
sprung from the Lycopodiales, or even from the Spheno- 
phyllalles. They have probably been derived more or less 
directly from that remote generalised group which combined 
the characters of Filicineae and Sphenophyllales. This very 
simple view would amply suffice to explain the peculiar mixed 
characters of this group. 
lsoctes is evidently closely allied to the Lycopodiales ; but, probably 
owing to its aquatic habit, it has retained certain characters 
of the same generalised ancestor which its modern allies 
have lost, probably owing to the specialisations induced by 
their land-habitat. 
