Obituary . — David Thomas Gwynne- Vaughan. xix 
perished. The rest of the structure, especially that of the petioles, appears 
to leave no doubt of the relationship to Osmundaceae. 
In the third memoir (K. and G.-V., 1909) other species from the Russian 
Permian are described, of which Thamnopteris Schlechtendalii (Eichwald) is 
much the most important. In this fine fossil conclusive evidence was found 
for protostelic structure, the inner region of the solid xylem consisting here 
also of large, thin-walled, reticulate tracheae. 
A full account was also given of the structure of the leaf-trace, which 
passes from mesarchy to endarchy in its outward course. A preliminary 
communication on this point had been published in the previous year (G.-V, 
and K., 1908. 2). The origin of the endarch from the mesarch leaf-trace was 
held to be general in the Filicales. 
In the ‘general conclusions’ of Memoir III the authors laid stress on 
the approach in the stem of Thamnopteris to the structure of Zygopteris 
corrugata , and predicted the discovery of a Zygopteris with a solid xylem 
and central short tracheae ; this was almost exactly realized immediately 
afterwards by Dr. Gordon’s discovery of the stem of Diplolabis , a Lower 
Carboniferous Zygopterid. 
The fourth memoir (K. and G.-V., 1910) is concerned with Osmundites 
Kolbei, Seward, from the Wealden of the Cape, and O. Schemn itzensis (Pettko) 
from the Miocene of Hungary. The latter is well preserved, but of ordinary 
structure. I n O. Kolbei , described externally by Seward in 1907, the pith 
- was much compressed, but the authors found that it contained undoubtedly 
tracheal elements ; they add : ‘ There is no doubt whatever that the 
tracheal elements are true and real constituents of the central tissue.’ They 
regarded this tissue, therefore, as a ‘ mixed pith ’, essentially similar to that 
in the stele of Zygopteris Grayi , if. corrugata , &c. Another point of interest 
in O. Kolbei was that the leaf-traces pass out without immediately causing 
an interruption of the xylem-ring, i. e. that the leaf-gap only begins some 
little distance above the outgoing trace. 
In this memoir the geological distribution of all the forms so far 
described is tabulated. 
The general discussion is of great value. The importance of Zenetti’s 
remarkable work on the structure of Osmund a, written long before there 
was any knowledge of the fossil history, is fully recognized. The Zygo- 
pterideae are discussed at length, in the light of Paul Bertrand’s elaborate 
investigations, and their relation to the Osmundaceae considered. The 
peculiar Zygopteridean frond, so unlike anything in recent Ferns, is regarded 
as derived from the type common to the Osmundaceae and the Filicales 
generally. 
The possibility is recognized that the Permian genera Zalesskya and 
Thamnopteris may eventually require a new Order, though on existing 
evidence they must be included in the Osmundaceae. 
