392 Stopes.—The Internal Anatomy of ‘Nilssonia orientalis\ 
The xylem of the bundle is apparently entirely centripetal for the small 
elements which appear to be protoxylem lie on the side towards the middle 
of the bundle (s eepx, Text-fig. and Fig. 4, PL XXVI). There are two or three 
of the small protoxylem-elements and about half a dozen cells of meta- 
xylem averaging o*oi mm. in diameter (x., Text-fig.). 
The phloem is hardly preserved, the only indication of its nature being 
the fragments of walls in the space below the xylem. 
Between the xylem and the bundle-sheath a few cells of soft paren¬ 
chyma are preserved. 
To sum up. The leaf has not a particularly differentiated epidermis 
or mesophyll. The bundles have each a fairly distinct bundle-sheath, and 
there are small strands of sclerenchyma above and below. The wood 
is entirely centripetal. The resin-canals appear to be very few in number, 
normal in structure, but very large, and running near the edge of the leaf. 
The leaf has a structure which is reminiscent of Cycads, and which 
might be looked upon either as primitive, or as lacking specialization owing 
to its habitat. What the habitat was we do not know. Although in living 
Cycads the xylem is usually mesarch, the bulk of the wood is centripetal 
and the centrifugal elements are apt to degenerate towards the apex, and 
in some species there are always very few of them. Those species of living 
Cycads which have resin-canals at all have them in numerical proportion to 
the bundles, usually one to each. But as some of the living Cycads have no 
resin-canals at all, it is not surprising to find a fossil in which so few are 
developed. 
The fact that all the wood in the bundle is centripetal might, not 
unreasonably, suggest a comparison with the several species of Cordaites in 
the Palaeozoic petrifactions which had only centripetal wood. I do not 
wish, however, to enter here into such a theoretical discussion about 
structures of the real phylogenetic value of which we know so little. Cordaites 
has been pressed into service rather frequently of late. 
For the present it suffices to describe the leaf as one which has a 
distinctly Cycad-like structure, but is simpler in general organization and 
in its vascular bundle than the living Cycad leaves. The fact that all 
its wood is centripetal might reasonably be considered as a primitive 
feature. 
A word must be said as regards the position of the species orientalis 
in the genus Nilssonia. Most writers place the Nilssonias in the Cycado- 
phyta, a classification which is confirmed by Nathorst’s last monograph. 1 
Nilssonia orientalis, Heer, resembles N. tenninervis , Nath., and differs 
1 Nathorst, A. G.: fiber die Gatt. AHlssonia Brongn. Kongl. Svenska Vetenskapsakad, Bd. 
xliii, No. 12, 1909. 
