258 
A. 0. Tansley. 
level this oval strand divides into two (the two compensation strands, 
which—traced upwards—here fuse and close a leaf-gap). The proto- 
xylem enters one of these two strands and soon dies out, about five 
internodes below the entry of the leaf-trace in O. regalis. It thus has 
no connexion with that of either of the leaf-traces entering below, on 
which the two forks respectively insert themselves. It is of interest 
to note that in Todea barbara, where the leaf-gaps are comparatively 
short (Fig. 84), each protoxylem strand can be traced down into the 
neighbourhood of the eighth leaf-trace below, where it dies out in 
one of the compensation-strands connected with that leaf, while in 
Osinunda regalis, where the leaf-gaps are very long, there is an 
independent xylem-strand running the same course (see above). 
Fig. 85. Todea barbara. Stele in transverse section showing relative 
lateral continuity of xylern. cf. Fig. 84. From Seward and Ford. 
Given the same phyllotactic spiral, with the same inclination to 
the horizon, the longer the leaf-gaps the more will appear in any 
given transverse section. If the phyllotaxy be simpler or the spiral 
runs at a steeper angle (i.e., if the leaves are less crowded) there 
will be fewer gaps in transverse section, and if the gaps are shorter, 
fewer still. In Todea barbara and T. superba the gaps are com¬ 
paratively short (Fig. 84) and consequently the xylem of the stele, 
as seen in transverse section, may consist of only two or three 
undulating bands of xylem (separated by as many gaps), in each 
of which several protoxylems have their course (Figs. 85 and 86). 
In Osmundites Dunlopi, a form recently described by Kidston 
and Gwynne-Vaughan (’07) from the Jurassic rocks of New Zealand, 
the xylem-cylinder is nearly, or perhaps quite, laterally continuous. 
