666 Browne. — Contributions to our Knowledge of the 
with the xylem-elements of one or both bundles, until these bundles, 
spreading towards one another, unite a little higher up ; but occasionally 
an island of tracheides first makes its appearance in the parenchyma 
between two of these widening strands, and the tracheides of the island 
increasing in number as we pass upwards, the island becomes united 
higher up to the neighbouring xylem-strands. In this case the island 
figures, in a longitudinal reconstruction of the xylem, as a small downward 
projecting tooth. Such ‘ interfascicular ’ xylem has at first no phloem 
outside it ; it not infrequently occupies a slightly more peripheral position 
than the xylem of the internodal strand. But as we pass upwards phloem 
very soon makes its appearance ; and when this has happened, and when 
the interfascicular tracheides have joined on to those of the internodal 
strand (from which they are indistinguishable in form), we get perfectly 
uniform bands, or in some cases a perfectly uniform ring of xylem. These 
bands or this ring of xylem is in most parts but one or two cells deep, 
though locally there may be three or even more cells on the same radius ; 
moreover, in a good many places there are internally to the bands or ring 
isolated tracheides or little groups of tracheides, usually of small size ; these 
may abut on the bands or ring of xylem, especially where these are rela- 
tively thick in a radial direction, or they may be separated from them by 
as many as three or four parenchymatous cells. Such tracheides or groups 
of tracheides do not as a rule persist for any considerable distance in a 
vertical direction ; in the internode they occur also internally to the separate 
strands of xylem (cf. PI. LXIV, Fig. 3). Some little way above the departure 
of the xylem of the traces these bands or rings of wood found at the nodes 
break up, portions of the band or ring ceasing to develop as tracheides. 
The narrow parenchymatous bands thus formed widen rather rapidly and 
constitute the parenchymatous meshes seen in a longitudinal reconstruction 
of the xylem (Text-figs. 1 and 2 and PI. LXIV, Fig. 4). These meshes are 
usually situated vertically above traces that have departed (in estimating the 
superposition of meshes to traces in a longitudinal reconstruction allowance 
must be made for the narrowing or widening of the diameter of the stele, 
which in the diagram causes a convergence or divergence of lines passing 
vertically upwards). A change in the number of members in the next 
whorl also tends to disturb the superposition of parenchymatous meshes to 
traces, since the xylem here breaks up into a number of strands different 
from the number of traces. Other irregularities will be considered later. 
Usually the parenchymatous meshes arise at a small distance above the 
traces. A glance at the reconstruction of the xylem in Cone A (Text-fig. 1) 
will show that the vertical height of the xylem persisting above the trace of 
a sporangiophore is not very different from the height of nodal xylem per- 
sisting above a leaf-trace (allowance must be made for the fact that the 
apical internodes of this very young cone have elongated even less than the 
