526 
Note. 
the structure of the plant, and to give for the first time a complete 
account of all its vegetative organs. 
A. The Stem. 
1. General Structure. — The middle of the central cylinder or stele 
is occupied by a parenchymatous pith. Surrounding this is the 
primary wood, which usually forms a ring of from five to eight distinct 
strands. Beyond this we find, in all but the youngest specimens, 
a broad zone of secondary wood, then the cambium, and next the 
phloem. The whole stele is bounded by a well-marked pericycle. 
The inner cortex is mainly parenchymatous, while the outer zone 
consists of alternating strands of fibres and parenchyma, constituting 
the well-known 1 dictyoxylon cortex ’ of Count Solms-Laubach. 
The pericycle and cortex are traversed by the leaf- trace bundles, 
which alternate with the perimedullary xylem-strands. 
2. Course of the Vascular Bundles. — We have obtained direct proof 
that the perimedullary strands of xylem form the downward continua- 
tion of the bundles which pass out into the leaves. Thus the entire 
bundle-system of the stem is built up of the leaf-traces. Each leaf- 
trace extends through at least ten internodes ; five internodes are 
traversed while it is passing through cortex and pericycle, and five 
more after it has reached the periphery of the pith. On entering the 
pith the trace turns aside in the kathodic direction, and unites with 
the adjacent perimedullary strand on that side. We thus see that 
these strands are sympodial bundles, made up of the united lower 
portions of adjacent leaf-traces.- 
In the upper part of its course, each leaf-trace consists of two 
bundles, which unite into one in passing through the pericycle. 
The phyllotaxis was usually two-fifths, but in the smallest stems 
was probably one-third. 
3. Structure of the Vascular Bundles. — The preservation is so good 
that we have been able to determine with certainty that the bundles 
in the stem were normally collateral , having xylem in their inner, 
and phloem on their outer side. As they passed out into the leaves 
their structure became concentric , the phloem here extending all 
round the xylem. 
The xylem of the bundles in the stem of Lyginodendron exactly 
resembles that in the leaves of existing Cycadeae. The protoxylem 
lies in the interior of the primary wood, but near its outer side, so 
