On the Real Nature of the Tracheae in the F eras. 
BY 
D. T. GWYNNE-VAUGHAN, M.A., F.L.S., 
Lecturer in Botany at Birkbeck College , London. 
With Plate XXVIII. 
HE following observations were originated by an investigation recently 
-L carried on by Dr. Kidston and myself into the structure of certain 
fossil Osmundaceae . 1 In some of the specimens that were examined the 
preservation of the xylem was unusually good, and much information was 
obtained concerning the detailed structure of the tracheal walls. It was 
found, however, that our observations on the fossils could not be brought 
into agreement with the prevalent idea of the structure of a Fern tracheide. 
This necessitated a re-examination of the xylem of some of the recent Ferns 
in order to see if this difficulty could not be explained away, eventually 
leading to the following unexpected conclusions : — 
In the first place, it may be stated that the metaxylem of the Filicales 
is generally regarded as consisting, for the most part, of typical scalariform 
tracheides ; the typical scalariform tracheide possessing a single series of 
pits on each of its sides or facets. Very few exceptions to this statement 
have as yet been recorded. The £ tracheide ’ type of element is known 
to be departed from in two cases only : Pteris aquilina and Nephrodium 
filix-mas (in the root). In these it is stated that true perforations occur in 
the end walls of the tracheae, which must, therefore, be regarded as vessels . 2 
As regards the kind of pitting, it is known that more than one series of pits 
occur constantly on the same facet in the xylem elements of Botrychium , 3 
Helminthostachys , 4 and in certain Botryopterideae. 
1 Kidston and Gwynne- Vaughan, ‘ On the Fossil Osmundaceae,’ parts i and ii, Trans. Roy. Soc. 
Edin., vol. xlv, part iii, p. 759, 1907, and vol. xvi, part ii, 1908. 
2 Russow, ‘ Vergleichende Untersuchungen,’ Mem. de l’Acad. Imp. des Sc. de Saint-Petersb. , 
Bd. xix, p. 103, 1872. 
3 Idem, p. 1 18. 
4 Farmer and Freeman, ‘ Affinities of Helminthostachys zeylanica Annals of Botany, vol. xiii, 
P- 433 , 1899. 
[Annals of Botany, Vol. XXIII. No. LXXXVII. July, 1908.] 
