700 G wynne- Vaughan. — Observations on the 
gaps, but occasionally, both in the main axis and in the 
lateral shoots, one or the other, or even both of these features 
may be wanting. 
Seward and Dale 1 have described a thickening of the 
margins of the leaf-gaps in Dipteris conjugata (Reinw.) which 
should probably be regarded as of the same nature as that in 
Dicksonia adiantoides , only a step more advanced. For in 
this case it appears that the free xylem-strand has almost 
separated off from the solenostele altogether, being connected 
with it only at two points, between which a tongue of ground- 
tissue has inserted itself. 
From the description given by Boodle 2 3 it appears that 
a structure very similar to this is also to be found at the 
margin of the leaf-gaps of Gleichenia pectinata , and it is 
suggested that here again we have to deal with the same 
phenomenon as in Dipteris conjugata and Dicksonia adian- 
toides . One point of difference, however, is to be noted 
in the two last cases, which is that both flanks of horse-shoe- 
shaped leaf-trace depart at the same time, and both sides 
of the leaf-gap are similarly thickened. 
Before going on to describe the internal vascular strands 
that occur in the stem of Dicksonia rubiginosa it is necessary 
to point out certain very exceptional features that are also 
presented by the ordinary vascular cylinder of this plant. 
The habit of the rhizome and the insertion of the leaf-traces 
are essentially the same as in Dicksonia adiantoides. The 
leaf-gaps close up directly after the leaf-trace departs (Fig. 13), 
but nevertheless the vascular system cannot be regarded as a 
solenostele, because in addition to the leaf-gaps other lacunae 
occur in the stelar cylinder which have no relation to the leaf- 
insertion whatever. These lacunae occur somewhat irregularly, 
but chiefly along two lines on opposite sides of the creeping 
rhizome. They are sometimes comparatively short, but more 
1 Structure and Affinities of Dipteris, &c., Phil. Trans., Series B, vol. cxciv, p. 
499, and Fig. 4, 1901. 
3 On the Anatomy of the Gleicheniaceae, Annals of Botany, vol. xv, no. lx, 
p. 730, 1901. 
