Lycopodium complanatum and Lycopodium clavatwn . 229 
sporophyte being more or less round in transverse section, while that 
of the mature plant is like a flattened triangle, owing to the shape of the 
leaves and their fusion with the stem. They are fused in such a manner 
that the chief part of the cortex, consisting of radially elongated assimilating 
cells, belongs equally to the leaves and stem, and this distinguishes the 
cortical tissues from those of the young plantlet, in which the assimilating 
cortical cells run in a vertical direction. Another difference lies in the 
distribution of the stomata ; these occur all round the stem of the young sporo- 
phyte, but are confined to the flattened ventral side of the mature stem. The 
creeping underground part of the stem of the mature sporophyte naturally 
shows greater differences. Here the stem Is much more bulky and circular 
in transverse section ; the number of protoxylem groups has Increased to 
a dozen or more, and these are connected in twos or threes by metaxylem 
in such a manner that the well-known banded arrangement is produced. 
The parenchymatous zone round the xylems is more pronounced, and the 
walls of the cells of the inner cortical zone have thickened so much that 
only very small lumina are left The presence of large intercellular spaces 
in the surrounding cortical layers and stomata in the epidermis, together 
with the fact that small leaves provided with vascular bundles occur at 
intervals, indicate an ancestral condition in which this part of the stem was 
also aerial. Evidence drawn from the study of the young sporophyte seems 
to point to the view that the radial arrangement of xylem and phloem 
occurring in the upright form of Lycopodium is the more primitive 
condition, and this Is supported by evidence from fossil forms of the 
Lycopod tales.. 
(d) Branching of the Stem . The branching of the stem, as in the 
roots, is dichotomous. This may begin very early, but in most cases the 
growth of one of the branches is stronger than that of the other, and so 
sections taken immediately below the dichotomy show one of the two steles 
smaller than the other. In the case of the pseudo-adventitious bud, the 
growth of one of the branches of the dichotomy is arrested for a consider- 
able period, and it remains as a bud protected by a few leaves until 
favourable circumstances arise for the continuation of its growth, and then 
not only apical growth occurs, but a root may be produced at the base, 
rt. PL XXII, Fig. 15, so that if separated off from the main plant it could 
lead an independent existence. 
(e) The Apex of the Stem. Longitudinal sections were made through 
the apex of the sporophyte shown in PL XXII, Fig. 2. This had dichoto- 
mized, and one of the branches had grown rather longer than the other. The 
shorter branch had just dichotomized, and showed at the apex two smaller 
groups of cells forming somewhat flattened cone-shaped structures about 
equal in size. A definite apical cell could not be made out ; the actual 
apex appeared to be occupied by several large cells equal In size,, from which, 
