Filicalcs . 
25 
we may note the polyarchy of their roots, rare among Ferns, and 
the fact that the Marattiaceous leaf-trace is a modification of the 
C-shaped type found in Psaronius. On the whole these resemblances 
suggest that the Marattiaceae were derived from the Psaronieae or 
their near allies, though, owing to the doubts that have arisen 
concerning the fructifications of Psaronius, this evidence is not so 
strong as it was thought to be. The ontogeny of the stele of the 
Marattiaceae does not support the view that they are reduced from 
more complex forms, so that, if descended from the Psaronieae, they 
probably arose from the simpler types. 
Ophioglossace.e. 
Only the Ophioglossaceae remain to be considered. Of the 
three genera of this order HehuintJiostacJiys comes nearest to the 
hypothecated protostelic ancestor; its xylem is mesarch while that 
of the other genera is endarch. In them the whole of the centripetal 
xylem has been lost and replaced by pith and centrifugal wood, 
while in Helmintliostachys this process is not complete. A further 
progression may be traced in Helmintliostachys, Botrychium and 
Opliioglossum. In the first genus, xylem and phloem form a ring, 
broken only by leaf-gaps (13); in the second the xylem, though not 
the phloem, has become broken up into approximated strands, while 
in Opliioglossum xylem and phloem are broken up and associated in 
collateral bundles separated by wide medullary rays. But Ophio- 
glossum always passes through an ontogenetic stage in which, as in 
Helmintliostachys, xylem and phloem form a ring, broken only by 
leaf-gaps (24), and this stage may be retained by the mature rhizome 
of 0. Bergianum (4). It would seem natural to regard the secondary 
growth in thickness of Botrychium as a recent acquisition, and its 
absence from the relatively simple Helmintliostachys favours such a 
view, but the presence of a little secondary xylem in so small a form 
as Opliioglossum vulgatum is puzzling on this hypothesis. 
The sporangia of this order are borne on one or more usually 
adaxial spikes, the nature of which has been much discussed. But 
as the spikes are clearly homologous throughout the order, the 
question is whether the forms with fewer and simpler spikes and 
fronds less often divided are more primitive than those with more 
highly compound fronds and more numerous and branched spikes. 
In Opliioglossum vulgatum and 0. pendulum the lamina is normally 
unbranched and bears a single spike adaxially; in 0. palmatum the 
compound lamina bears one to fourteen spikes. In Botrychium the 
adaxial spike is usually pinnately branched and may be three or 
