Scott. — On Peduncle of Cycadaceae. 415 
As regards the development of the centripetal xylem, 
Poroxylon is about on a level with Lyginodendron Old - 
hamium ; but in the former this tissue dies out towards 
the lower end of each leaf-trace bundle, about seven or 
eight internodes below the point where it enters the 
stem 1 . Poroxylon seems to show distinct affinities with 
the Lyginodendreae on the one hand, and the Cordaiteae 
on the other. 
Ultimately the stem retained centrifugal wood only, as 
in the Cordaiteae, and in recent Cycads, with the exceptions 
recorded in the present paper. We must not suppose that 
the whole of the centrifugal wood was secondary in origin. 
In Lyginodendron and Heterangium , the primary xylem has 
a well-marked centrifugal portion 2 . The same is clearly the 
case in many foliar bundles of recent Cycads, though some- 
times the limit between primary and secondary tissue may 
be impossible to define. 
The view maintained in the present paper as to the evolu- 
tion of the vascular bundles in Gymnosperms has much in 
common with that put forward by MM. Bertrand and Renault 
in 1886 3 . These authors, however, assumed that the whole 
centrifugal part of the wood is secondary, an assumption 
which hangs together with their attempt to derive Cycads, 
Poroxylon , and Lyginodendron from Lycopods and not from 
Filicineae. This view is no longer tenable. Both recent 
Cycads and their fossil allies (Bennettiteae, Lyginodendreae, 
Medulloseae) abound in Fern-like characters, and have simply 
nothing in common with Lycopods. Lyginodendron , for 
for the secondary tissue, sometimes developed at the margin of the pith in 
Lyginodendron and Cycadoxylon. This terminology is of course quite legitimate, 
but it is important to avoid confusing this anomalous secondary formation with the 
centripetal xylem which forms part of the primary structure of the bundle. The 
latter is simply termed ‘ primary wood 5 by Mr. Seward. On Cycadoxyleae see 
Renault, Flore fossile d’Autun et d’Epinal, Part 2, 1896. 
1 Bertrand et Renault, Recherches sur les Poroxylons, Archives Bot. du Nord 
de la France, 1886-7 5 also Remarques sur les faisceaux foliaires des Cycaddes, 
loc. cit. p. 238. 
2 Williamson and Scott, loc. cit., pp. 713 and 749. 
3 Remarques sur les faisceaux foliaires des Cycadees, loc. cit. 
