194 Gibson . — Contributions towards a Knowledge 
this statement, and pointed out how in inaequalifolia these 
dorsal and ventral accessory steles arise. 
It will have been seen, from the data given in some detail 
in the first section of this paper, that several distinct types of 
stem-structure may be distinguished. I propose now to give 
a brief summary of these types, arranged in the order of what 
seems to me their phylogenetic development. 
1. 5. laevigata , Baker, var. Lyallii , Spr. 
In this form a distinct rhizome gives origin to a series of 
erect shoots on the one side and roots on the other. The 
rhizome contains a cylindrical hollow stele, with protoxylems 
on the outer border of the xylem. The centre of the cylinder 
is occupied by parenchyma, or by a cord of metaxylem with- 
out protoxylem-elements, derived from the inner margin of 
the cylindrical stele. The cylinder opens opposite the point 
of origin of each of the erect shoots, and the steles of the erect 
shoot are inserted on the upper (dorsal) border of the mesh, 
and are connected also with the central cord, which in this 
region fuses with the cylindrical stele. The erect shoots 
possess four primary cords, on which the leaf-traces are 
inserted, and several accessory cords which anastomose with 
each other and with the primaries. The ultimate branchlets 
are tristelic, as in the normal tristelic species. At the union 
of such a branchlet and the more vigorous axis possessed of 
four cords in two lateral pairs, the members of which are dorsal 
and ventral, the inner stele of the branch fuses with the dorsal 
stele of the pair of that side, the outer with the ventral. The 
trace of the axillary leaf is inserted on the ventral stele. 
2 . vS. spinosa , P.B. 
In this type there is no marked distinction between 
procumbent and erect axes ; the stem is at first creeping 
and then becomes erect or semi-erect. The creeping portion, 
however, shows the anomaly of having a central protoxylem. 
The erect portion of the shoot may be compared with the 
creeping rhizome of 5. Lyallii , for there also there occurs a 
single cylindrical stele with protoxylems on the outer border 
of the metaxylem, which are the points of insertion of the 
