Lycopodium complanatum and Lycopodium c lav at am 227 
In the upper part of the older sporophyte of L. complanatum a ten- 
dency towards the banded arrangement is shown ; the xylem mass, which 
here is six-rayed, has become separated into two by a band of phloem. 
In this region also and in the older parts of L. clavatum a layer of cells 
occurs between the protoxylem and the c pericambium/ which resemble 
the phloem-cells in general appearance and in the staining properties of the 
walls. Yan Tieghem calls the band of cells, one to several layers thick, 
between the endodermis (protective sheath) and the xylem the pericycle, 
and regards it as part of the central cylinder. Strasburger and Rruch- 
mann on the other hand, consider that this pericycle has the same origin 
as the cortex. I find that in the lower part of the stem the protoxylem 
elements do lie next to. cells of cortical origin, occasionally next to the 
protective sheath itself, but that in the upper part of the older sporophyte 
there is a layer of cells which belongs to the central cylinder lying between 
the protoxylem and the cells of cortical origin, and probably representing 
phloem-cells. This latter condition agrees with that of the mature stem, 
where there is generally a ring of thin-walled cells lying between the 
protoxylems and the endodermis which resemble the cells surrounding 
the sieve- tubes between the xylem rays. The view that this layer outside 
the xylem. represents phloem does not seem inconsistent when one considers 
the irregular course which the xylem strands take through the stem of the 
young sporophyte, and the fact that the leaf-traces play an important part 
in the constitution of the central stele, except in the lower part of the 
young sporophytes. 
According to Campbell 2 the complete .stem of Lycopodium possesses 
two systems of vascular bundles, the strictly cauline central cylinder and 
the system of common bundles formed by the leaf-traces. 
In the lower part of the young sporophyte the central stele is strictly 
cauline. The first indication of anything approaching a leaf-trace is the 
spiral marking of some of the cortical cells which are in connexion with 
the base of the scale. In a slightly more advanced stage the leaf-trace is 
represented by exceedingly narrow tracheides which leave the main stele 
at the edge of one of the protoxylems. Higher up, where the leaves have 
reached the light and are better developed, the structure of the leaf-trace 
is more complicated, the number of elements increasing as it passes through, 
the cortex. The leaf-trace leaves the main stele at the end of the xylem 
plates and takes an upward course through the cortex, making an acute 
angle with the central stele of the stem, while near the periphery it takes 
a more horizontal course. A section taken just above The point where it 
leaves the stele of the stem shows a well-defined mass of xylem consisting 
of tracheides which in transverse section appear to be full of granules owing 
1 Bruchmann, loc. cit., p. 55. 2 Campbell, Mosses and Ferns (new edition), p. 495. 
