Fill cates. 
241 
The simpler forms of both orders are protostelic; in the Schizaaaceae 
these simpler forms are exarch and the present writer holds that 
the Botryopterideae were also primitively exarch, but this is doubtful 
and denied by many. But though the simpler types of both orders 
are not very different anatomically, it seems unlikely that the 
dichotomous fronds of some of the Schizaeaceae should have been 
derived from the pinnate ones of the Botryopterideae. Potonie has 
laid great stress on the primitiveness of dichotomy in Fern-fronds 
and its prevalence in the fern-like fronds of the Palaeozoic rocks 
(21), and his views have met with very general acceptance (18), (30). 
Moreover, although the Schizaeaceous annulus may be two cells 
broad, it is not easy to derive it from the annulus of any annulate 
Botryopterideae, though of course it might have originated from one 
of the exannulate members of the order. Thus it is unlikely that 
the Schizaeaceae are directly descended from the Botryopterideae, 
but they may have arisen from simpler allies of the latter, from 
some of the Primofilices of Mr. Arber. Like the Hymenophyllaceae, 
the simpler Schizaeaceae are protostelic ; this probably indicates a 
low stage in the evolution of the stele rather than a particularly 
close relationship between the two orders. As it was concluded 
that the Hymenophyllaceae were a series of reduction, we shall not 
be astonished to find that the least reduced Hymenophyllaceae, such 
as Trichonianes scandens, are most like the simpler Schizaeaceae, 
such as Lygodium. A striking point of similarity is the occurrence 
of filamentous prothalli in members of both orders. This probably 
does not indicate close affinity, for the filamentous prothalli would 
appear to be secondary in both orders. The structure and origin 
of their sporangia is, however, essentially similar, though their 
distribution is different. According to Professor Bower’s researches 
the annulus is probably homologous in the two orders (7). These 
characters hardly warrant the assertion of a very close affinity, but 
they suggest that both orders originated from allied groups of the 
Palaeozoic Primofilices. 
GlEICHENIACE/E. 
The Gleicheniaceae are always protostelic, except the soleno- 
stelic Gleichenia pectinata, and Platyzoma, which possesses an 
ectophloic siphonostele. There is of course a strong presumption 
that the protostelic condition is primitive and that the solenostele was 
derived from it. In connection with the insertion of the leaf-trace, 
a “ nodal island ” is found in most of the protostelic Gleichenias. 
