Sinnott—Some Jurassic Osmundaceae from New Zealand. 475 
very likely that the Zygopterideae and Osmundaceae, and all other modern 
families of Ferns as well, may have descended from an ancestor of this 
general type. The upshot of the whole matter seems to be that, so far as 
their anatomy is concerned, the evidence for a close relation of the two 
families in question is not very convincing. 
Much stronger evidence in favour of the intrastelar origin of the pith 
is furnished by the structure of the Jurassic genera Zalessky a and 
Thamnopteris (1), which from the character of their leaf-trace and petiolar 
bundle seem clearly to belong to the Osmundaceae, though both are 
protostelic, with no parenchymatous pith. In the centre of the stele, 
however, is a sharply differentiated region of short, wide vascular elements, 
which is held to be the forerunner of a true pith. 
The idea that these fossil Ferns are the direct ancestors of the typical 
medullated Osmundaceae is very plausible, but, unfortunately for the theory, 
Zalesskya and Thamnopteris are definitely protostelic, and have no traces 
even of wood parenchyma. Moreover, no indisputably intermediate forms 
between them and a medullated condition have yet been found. 
The nearest approach to such a transitional type is Osmundites Kolbei , 
described from the Jurassic of South Africa by Kidston and Gwynne- 
Vaughan (1). The stem of this species is in a poor state of preservation, 
with the central cylinder much flattened, but the authors find in the pith 
one or two definite strands of vascular tissue, which they interpret as 
remnants of the originally solid vascular core which have failed to be 
converted into parenchyma, and which form part of a true ‘ mixed pith \ 
It is in this connexion that our Waikawa fossil is of interest, for it is in 
a much better state of preservation than O. Kolbei , but like that species 
shows definite strands of vascular tissue in the pith. As we have pointed 
out, however, these are very obviously roots, for the vascular bundle is 
diarch, like all Osmundaceous roots, and is surrounded by a definite cortex 
of its own which is sharply marked off from the disintegrating tissue of the 
pith. It is thus very doubtful if the vascular elements in the pith of 
O. Kolbei are to be regarded as remnants of an originally solid protostele. 
The evidence from more perfectly preserved material, and from living 
species as well, indicates that they are much more probably roots. 
It must therefore be admitted that no indubitably transitional forms 
between the protostelic Osmundaceae, and those with a true pith, have yet 
been discovered. Nor is the evidence at hand sufficient to prove that the 
latter must have come from the former through such a type as Thamnopteris. 
It is very possible that protostelic and siphonostelic Osmundaceae existed 
side by side since the origin of the family, for other groups of Ferns exhibit 
similarly fundamental differences in the topography of the stele between 
closely related forms. The protostelic Lygodium and the siphonostelic 
Aneimia are both members of the Schizaeaceae, and in the single genus 
K k 
