476 Sinnott. — Some Jurassic Osmundaceae from New Zealand. 
Gleichenia there are some species with, and others without, a pith. Glei- 
chenia pectinata, for example, has a pith continuous with the cortex through 
the wide leaf-gaps and morphologically identical with it, according to the 
ordinary interpretation. If the gaps should become much narrower, 
affecting only the xylem of the stele, and if the internal phloem and 
endodermis should disappear, the pith in this genus would undoubtedly be 
explained by many as merely a large aggregation of the parenchymatous 
tissue, which is abundantly present throughout the xylem of the protostelic 
species. Such an explanation would of course not be tenable if the 
members of the reduction series from G. pectinata to the hypothetical form 
in question were known. 
The theory proposed by Jeffrey supposes that the ancient Osmundaceae 
were in somewhat the same state as the genus Gleichenia is in to-day, and 
possessed some forms with a solid stele, which gave rise to the Tharnno- 
pteris type, and others with a true pith and wide leaf-gaps, from which the 
Jurassic and modern siphonostelic forms have been developed by reduction. 
Thamnopteris and other protostelic Osmundaceae are considered on this 
view as divergent lines which led nowhere, and finally disappeared. 
Strong evidence in favour of this theory is presented by such fossils 
as Osmundites Skidegatensis , which is characterized by internal phloem 
and the continuity of pith and cortex through the wide leaf-gaps. The 
more recently described O. Carneri (5) from Paraguay shows a similarly 
large stele and wide gaps. Such forms provide just the intermediate 
condition which Jeffrey’s theory postulates between a normal siphonostele 
and the reduced state of the modern Osmundaceae. The importance of 
these fossils has been minimized because of their supposedly recent geo- 
logical horizon, but in the case of O. Skidegatensis there is now doubt as to 
whether it should not be referred to the Jurassic instead of to the Cretaceous ; 
and O. Carneri is very possibly Jurassic. 
A shortening of the internode, and a narrowing of the leaf-gaps in 
such forms, would produce a stele much like that of O. Dunlopi , O. Kolbei , 
and others, where gaps are very narrow and often apparently absent. We 
have already considered the probability that the invariable presence of 
leaf-gaps could be determined if preservation were sufficiently perfect. On 
the intrastelar theory of the pith these narrow but persistent gaps fail of an 
explanation, for no sign of a deep and narrow indentation opposite the leaf- 
trace is evident in the cylinder of Zalesskya or Thamnopteris. On the 
reduction theory, however, the gaps are of significance as a notable 
retention of the character of phyllosiphony, which is so distinctive of all 
siphonostelic members of the Pteropsida. 
The controversy over the morphology of the stele in the Osmundaceae 
will doubtless long continue, and can be settled conclusively only by a dis- 
covery of the fossil ancestors of the family, and by an actual reconstruction 
