MARATTIACEAE 523 
see, the comparison is confirmed by reference to the petrified stems known 
as Psaronius. This consideration will justify our drawing together the 
modern and the fossil forms into a comparison with a view to tracing 
~ probable phyletic changes in the structure of the sorus, and a recognition 
of an original type.' The definitely circumscribed sorus appears to be 
a characteristic of the Marattiaceae, both ancient and modern. The form 
of the sorus varied from circular to elongated, both in the fossils and in 
_ living forms: there is no distinctive stratigraphical evidence to show which 
type was the prior, but in the majority of the early fossils the sorus is 
circular, with a small number of 
sporangia. Further, the Pecop- x 
terid is a relatively narrow-leaved BA 
type, while the leaves of Danaea =2 
and Kaulfussia are broad: if a =e 
Vi 
widening of the leaf took place, 
followed by extension of the A e 8 
E Fic. . 
sorus, the result would be as in ae 
F : . Danaeites saraepontanus, Stur. From the upper car- 
Danaea or Danaeites: if abstric-  boniferous of the Saar district. A =a fertile segment of 
: . the last order. =transverse section through two adjoin- 
tion of the elongated sori followed ing sori, or the hollow impression of them. C=below a 
. sorus of sixteen sporangia; above the impression of it. 
also, the result would be as in (After Stur. From Engler and Prantl, Vaz. Pflanzenfam.) 
Kaulfussia. The evidence of the 
partial septa in Danaea, and the irregularity of size and segmentation of 
the sporangia throughout the family, accords with the suggested extension 
of an originally circular sorus with few loculi to produce the more or 
less elongated sori of the living forms with more numerous loculi. 
A further point for discussion is the original relation of the sporangia 
to one another in the sorus. Among both ancient and modern Marattiaceae 
various gradations may be seen between such as have their sporangia 
quite separate, and those in which they are synangially united. On this 
point the palaeontological evidence would be consistent with either view, 
for neither the synangial nor the polysporangiate state is distinctly the 
prior in stratigraphical sequence. It becomes thus a question of comparison, 
rather than of demonstration. As a matter of fact, all Marattiaceous sori 
are synangia in the first phases of their ontogeny: many of them remain 
so to maturity. It is only as the individual development proceeds that 
the sporangia project as individual outgrowths in such a case as that of 
Angiopteris. So far then as individual development bears on the question, 
it would indicate the synangial state as the more primitive. Reasons have 
already been shown for holding that a progressive septation accompanies 
the extension of the sorus in the type of Danaea: a similar septation of 
an enlarging initial spore-sac would produce the type of sorus seen, for 
instance, in Ptychocarpus. Such an origin would consistently carry back to 
an initial point that process of septation which is seen to be effective in 
Danaea. From the synangial state thus produced the polysporangiate state 
1A more full statement of the arguments is given in Studzes, iii., p. 67-77. 
