Sinnott. — Some Jurassic Osmundaceae from New Zealand . 473 
apparently absent. Its state of preservation is very much poorer than that 
of our Kawhia specimen, however, which shows the universal presence 
of very narrow gaps, and it is logical to infer that, were the structure of 
O. Dunlopi less crushed and disorganized, gaps would be evident there also. 
The agreement in petiolar structure, which is an important diagnostic 
feature in the Osmundaceae, is even more precise, for both O. Diinlopi and 
the fossils under consideration show two large patches of sclerenchyma at 
the base of the stipular wings, and two others inside the lateral bays 
of the leaf-trace, thus differing from all other members of the family. The 
occurrence of roots in the pith of the Waikawa specimen is not considered 
a diagnostic character. 
The resemblance of the fossils here described to O. Dunlopi is 
therefore close enough to warrant our regarding them as members of that 
species, which seems to have been widely distributed in New Zealand in 
Jurassic time. 
Discussion. 
It remains to discuss what bearing the structure of these fossils has on 
the morphology of the Osmundaceae. The view that the living members 
of the family primitively possessed an amphiphloic siphonostele with wide 
leaf-gaps, similar to that of most modern Ferns, and that the present 
structure has been derived by reduction from such a condition, with the 
loss, in most cases, of internal phloem and endodermis, has been put forward 
by Faull (2), and by Jeffrey (3). This hypothesis has met with vigorous 
opposition from the majority of anatomists, most of whom contend that in 
the Osmundaceae, and also in the Ophioglossaceae, the pith has had an 
entirely different origin from that in all other Pteridophyta, and that it has 
been derived by the direct conversion into parenchyma of the vascular 
elements in the centre of the primitive protostele, without having any 
original morphological connexion with the cortex. 
Which of these views is the correct one cannot be settled a priori 
by an appeal to any general law of evolution. It may well be that the 
pith of vascular plants has been derived in two entirely different ways, for 
it often happens that two very similar structures are morphologically 
different, and have had an entirely independent evolutionary origin. But 
the fact that in the vast majority of all medullated vascular cryptogams, 
and apparently in the higher plants as well, the pith is at least primitively 
in direct connexion with the cortex, and morphologically equivalent to it, 
and the presence in fossil and living Osmundaceae themselves of many 
structures which are hard to account for, unless we assume that reduction 
from the ordinary condition has taken place in this series, furnish a very 
strong presupposition in favour of the theory of a uniform method of 
medullation among all vascular plants. The burden of proof is clearly 
