DENNSTAEDTIINAE 601 
This simple vascular structure holds for most species, with minor modifica- 
tions of form of the leaf-gap, and of insertion of the supply for lateral axes. 
There is, however, a further com- 
plication in Dennstaedtia adiantoides 
and rudiginosa: in the former a 
local thickening appears internally 
at the margins of the leaf-gaps in 
the ordinary stelar cylinder: this 
becomes extended to form an in- 
wardly projecting ridge, continuous 
from one leaf-gap to another (Fig. 
333 B). In D. rubiginosa this ridge 
is represented by a separate strand, Fics 333 C. 
which still maintains its connection 
with each leaf-gap-margin, but may {, sseylar system of the chizome including 2 node, 
divide into several distinct rods 333 2: @=lacunae in the solenostele not related to 
the departure of a leaf-trace. The upper surface of 
(Fig. 333 C). This peculiarity is oo would face the observer. (After Gwynne- 
Dennstaedtia (Dicksonia) rubiginosa. Diagram of 
of importance for comparison with 
what is seen in the stems of the Pterideae on the one hand, and of the 
Cyatheae on the other, while it also has its bearings in the elucidation of 
the complex structure already seen in the Matonineae. 
These facts of vascular anatomy, coupled with those relating to the 
sorus appear to indicate for the Dennstaedtiinae a very interesting inter- 
mediate position. On the one hand their confirmed solenostely is evidence 
of a relatively primitive state, derived probably from a protostelic source ; 
but it shows only slight indications of passing onwards to the more 
advanced state of dictyostely. Moreover, the constant condition of the 
leaf-trace as an undivided, ribbon-like strand is a clear index of their 
primitive position. Similarly, the uniform occurrence of hairs and the 
absence of ramenta points to the simpler rather than to the more advanced 
Filicales. 
On the other hand, the soral conditions are characteristically those 
of the Gradatae: the basipetal sequence of sporangia is quite as marked 
as in Daucksonia or Loxsoma, with which they share the basal indusium, 
here, as in JDycksonia, two-lipped. But in certain species occasional 
departures from the strict basipetal sequence occur: these are most 
prominent in Dennstaedtia rubiginosa, a species which shows also the 
vascular strands within the solenostele. With the loss of basipetal succession 
and the advent of the elongated stalk the sporangium loses its regularity 
of orientation and its markedly oblique annulus. But this is what might be 
expected, since there is no longer any mechanical reason for the regularity. 
In both of these characters, of anatomical structure and of sorus, the 
Dennstaedtiinae approach the Pterideae. On the other hand their relation 
to Dicksonia and to Loxsoma is clear: it is based primarily upon habit 
