34i 
of Lepidostrobus Brownii, Schpr. 
may be quoted, though it must at the same time be admitted 
that the similarity depends rather upon the absence than the 
presence of definite characters in the tissues. 
Such being the structure of the bundle in its course through 
the inner cortex, it must now be traced outwards to the more 
lax tissue of the middle cortex, and the first change which 
appears is the elongation of such cells as are marked (%) in 
Fig. 4 A and B ; intercellular spaces also appear between them 
(Fig. 5), and the bundle thus becomes surrounded by a lax, 
lacunar tissue (Fig. 6). The enlargement of the spaces and 
elongation of the cells finally results in the partial (Fig. 7), 
or complete isolation of the bundle (Fig. 8, A and B ), from 
the surrounding ground-tissue, except in so far as a con- 
nexion is maintained by the elongated trabeculae. It will 
be at once seen that these trabeculae, originating as they 
do from the irregular sheath surrounding the bundle, are 
very similar to the trabeculae of Selaginella. This comparison 
is strengthened by the apparent occasional presence of a ring- 
like zone round the trabeculae (Figs. 7 and 11), though this is 
not constantly to be seen, nor can much stress be laid upon 
such a point in dealing with a fossil. As the bundle 
approaches the outer limit of the inner dense zone of cortex, 
the trabeculae elongate and the intercellular space extends 
all round the bundle, so that it finally emerges into the 
large ring-like cavity, so clearly seen in Fig. 1. The bundles 
are here quite isolated in the fossil, and appear as dots in 
Fig. 1 ; as they approach the outer dense band of cortex, 
trabeculae extends inwards from it towards the bundle 
(Fig. 8 A), showing broken ends, while the superficial cells of 
the bundle show similar evidence of broken attachment. 
It would thus seem probable that the connexion of the 
bundles by means of the trabeculae to the cortical tissue 
was, at least during earlier life, more complete than is now 
seen in the fossil state. 
The structure of the bundle as it traverses the space 
(Fig. 8) adds to the evidence of its collateral character ; it 
is surrounded, as is commonly the case, in Selaginella by 
Aa 2 
