of Lepidostr obits Brownii , Schpr. 349 
seen on a much smaller scale in L. inundatum or in the 
outer tissue of the cortex in Z. alpinum. It is interesting to 
note how tissues further removed from the bundles, or closer 
to them, may be involved in the trabecular development ; thus 
trabeculae may be independent in the cortex, as in Z. inun- 
datum (Fig. 14) or Z. alpinum (Fig. 15), or they may 
surround the leaf-trace bundle, while the latter is still pro- 
tected by several layers of connected tissue (Fig. 12), or the 
cells more directly surrounding the bundle, but constituting 
an ill-defined sheath, may take part in the trabecular develop- 
ment, as in Lep . Brownii (Figs. 5, 6, 7), so that the bundle 
itself appears suspended in a large cavity. It is a very slight 
step from such a condition to that so well known around the 
bundles of the stem of Selaginella. Here a definite sheath of 
cells is involved in the formation of the trabeculae *, the cells 
undergoing division after their separation laterally from one 
another. In Lep. Brownii the sheath is a less definite one ; 
the cells appear to undergo a somewhat irregular division 
before they separate laterally, and the trabecular development 
is only found around the leaf-trace bundles, not directly 
around the central stele. There are thus a number of points 
of difference between what is seen in Lep . Brownii and the 
well-known trabeculae of Selaginella. The sequence of ex- 
amples above quoted nevertheless seems to me to be suffi- 
ciently continuous to justify the conclusion, on comparative 
grounds, that the trabecidar development in Selaginella is 
a specialized and more definite example of that lacunar 
development which appears in such various forms and posi- 
tions in cortical tissues of various other Lycopodinous plants ; 
in the latter the lacunae are more generally distributed ; in 
Selaginella they are localized round the vascular masses ; but 
in all cases they owe their origin to the tissues outside the 
bundle. 
I do not anticipate that the detailed characters of structure 
of the cortex in these plants can ever be used as arguments of 
1 Treub. ; Rech. sur Selaginella Martensii , p. n, Figs. 15, i'j. 
