250 
Browne . — The A natomy of the 
to be accurately superposed to those of the second whorl in a downward 
direction, as they would be if the traces of successive whorls alternated quite 
regularly. * Speaking generally, where sufficient nodal xylem is developed 
for a number of laterally consecutive meshes to be closed, the traces given 
off from the band that is produced by these closures alternate more or less 
regularly with those of the whorl below. More or less regular superposition 
occurs, as in the other species studied, when the meshes on either side of 
a strand persist unnarrowed through a node, so that the strand gives off 
a trace without afterwards branching, i.e. without the formation of a mesh 
above the trace. Superposition of traces is not so common in the cones of 
the two species under consideration as in those of E. maximum and 
E. limosum, because the axial xylem is relatively better developed. 
Examples, however, occur in the three cones of E. hyemale as well as in the 
three of E. giganteum of which longitudinal reconstructions of the axial 
stele were made (cf. Text-figs. 2, 3, 4, 5, 6, and 7). In the last species I 
have not observed more than three successive traces to be inserted in the 
same vertical line, whereas in E. maximum and E. limosum the number 
may be as high as seven. In Cone A of E. hyemale, a cone which had 
a considerably better developed vascular system than Cones B and C of the 
same species, accurate superposition of the traces was rare, and I did not 
observe more than two successive traces to be inserted on the same vertical 
line. In Cones B and C of this species, however, I found that the number 
might be as high as four to six. Irregular alternation of traces is common 
in both species (cf. Browne (2), p. 239), and occurs most often when a band 
of xylem gives off one or more median traces and a lateral trace at either or 
each end. When we are not dealing with cases in which wide sweeps of 
xylem persist through the internode above, a parenchymatous mesh (or 
meshes) arises over the median trace (or traces) of such a band. No fresh 
mesh, of course, arises over the lateral trace or traces, and the strands 
formed by the breaking up of the band alternate irregularly with those in 
the internode below. When the strands narrow markedly above the node, 
owing to the dying out of the tracheides immediately above the lateral 
trace, the irregularity in the alternation is less. 
Both in E. giganteum and in E. hyemale the nodes of the cone vary 
very greatly in the amount of axial xylem developed, and therefore in the 
number of meshes closed. In E. giganteum it is common for some trace- 
bearing strands to remain isolated, and for others to become united in pairs, 
each pair remaining separated from neighbouring strands by relatively wide 
parenchymatous meshes. In such cases the incoming traces, which are, of 
course, entering the cortex from sporangiophores arranged regularly around 
the axis without regard to the persistence of wide parenchymatous meshes 
through the node, naturally tend to be inserted at or near each end of the 
band of xylem formed by the fused strands. Above such traces fresh 
