West. — A Contribution to the Study of the Marattiaceae. 369 
the junction of the earlier leaf-traces. This primary stele never has the 
form of a true protostele, however, as the xylems belonging to the separate 
leaf-traces can be recognized and the compound nature of this central 
bundle is unmistakable.’ 
It has already been pointed out that the sporeling of Danaea alata is 
radial in structure ; correlated with this fact, we find that the sympodium of 
leaf- and root-traces which together make up the vascular system of the 
young sporophyte is likewise based on a radial plan, the traces of the first 
few leaves being arranged in a rough spiral. 
It may be noted in passing that the vascular tissue of the embryo plant 
of other megaphyllous Vascular Crytogams (e. g. Ophioglossaceae, Isoetes) 
may consist solely of a system of leaf- and root-traces, hence it is not 
surprising that a similar condition should obtain in the remarkable 
megaphyllous Marattiacean Ferns. 
A distinct leaf-gap is formed by the trace of the sixth leaf, above the 
point of insertion of which the stem-stele is definitely crescentic in transverse 
section. Campbell(20) maintains that the stem-stele in this region still consists 
solely of leaf- and root-traces, but the present writer is of the opinion that 
part, at least, of the vascular tissue of the ‘ siphonostele ’ with large leaf-gaps 
(cf. Text-fig. 4, a) which marks the next stage in the elaboration of the 
stelar system of Danaea , is made up of elements which have a truly cauline 
origin and serve to connect up adjacent leaf-traces. 
A root-trace (Text-fig. 4, A, r.t. 4) joins the stelar cylinder above the gap 
formed by the trace of the sixth leaf ; in this region the siphonostele forms 
a complete cylinder (= solenostele) uninterrupted by leaf-gaps (the region 
indicated by a x in Text-fig. 4, A). The first commissural strand arises by 
proliferation of the vascular tissues on the inner surface of the stelar tube 
opposite the point where the trace of root 4 joins the stem -stele (above leaf- 
gap 6 in Text-fig. 4, A); considered from the point of view of water- 
conduction, this strand forms a direct continuation of the root-trace. 
Traced upwards, this strand passes across the medullary ground-tissue from 
the upper end of one leaf-gap to the apex of the next leaf-gap above, which 
it helps to close, and since, generally speaking, a root-trace joins the outer 
surface of the stem-stele at these points, the commissural strand at first 
forms an auxiliary internal conducting system of cauline origin, which 
continues to connect up the points of insertion of the relatively large and 
important root-traces. During these earlier stages, the commissural strand 
obviously fills a relatively subordinate position, as compared with the main 
stelar cylinder, but, as Brebner (12, p, 536) rightly pointed out, the special 
advantage of such an arrangement is obvious, since any root probably does 
not reach the soil until after the related leaf has unfolded. 
Now, whereas the trace of the seventh leaf consists of a single strap- 
shaped strand which splits into two whilst still within the stem-cortex, the 
