454 Browne. — A Fourth Contribution to our Knowledge of 
lie opposite the axial strand, the vascular supply as it passes gradually 
upwards and outwards through the bundle curves towards the sporangio- 
phore and comes to lie on a different radius from the parent strand of the 
axis. Thus it is shown as a separate broken line in the reconstruction. 
The cases in which the axial protoxylem is shown in the diagrams as 
passing straight and uninterruptedly upwards above the traces are of three 
sorts. Firstly, the protoxylem of the trace may pass out horizontally, and 
then the axial protoxylem does not branch below the trace ; or the proto- 
xylem of the latter may enter a sporangiophore on the same radius as the 
axial strand, and so never became apparent as a separate branch in the 
reconstruction ; or, lastly, such a trace may enter a sporangiophore to one 
side of the axial protoxylem, but the curvature of the trace may occur 
in the cortex (cf. Browne ( 2 ), p. 261, on the twisting of the traces in 
the cortex of E. maximum ). 
That the course of the protoxylem as well as the distribution of the 
metaxylem has been affected by reduction seems to me confirmed by 
the fact that in Cone B of E. sylvaticum the protoxylem entering the 
ninth sporangiophore of the eighth whorl, and that of the fourth sporangio- 
phore of the uppermost whorl, are not continuous with the rest of the 
protoxylem of the cone. The protoxylem of the axial strand giving rise to 
the ninth trace of the eighth whorl forms a particularly distinct canal, 
abutting at its lower end on very definite metaxylem tracheides. This 
means that in the ontogeny the cells just below the lower end of the axial 
protoxylem had reached a considerable size before they were differentiated 
as tracheides, and that such differentiation occurred later than the differen- 
tiation of the tracheides of the protoxylem immediately above them. 
We may perhaps recognize in the incomplete fusion of certain proto- 
xylems, which is one of the irregularities of the protoxylem ‘system’, 
a phenomenon associated with prematurely divided traces. Such approxi- 
mation of protoxylems, not leading to their junction, as is found, for example, 
at the point of departure of the eighth trace of the fourth whorl of Cone B of 
E. sylvaticum , causes the trace to originate as separate halves. This failure 
of two protoxylems to fuse into a single one is, it may be noted, associated 
with a failure of one of the strands to branch at the node below, and the 
persistence of the mesh through this lower node to a point just below 
the next node. In this case the metaxylem of the two strands, which fuses 
just before the fourth node, clearly reproduces the more primitive condition, 
lost by the protoxylem. 
' Summary. 
1. The vascular system of the cone of E. sylvaticum resembles on 
a smaller scale that of the cone of E . maximum ; relatively to its size 
it is better developed. 
3 
