KIDSTON : THE FLORA OF THE CARBONIFEROUS PERIOD. 365 
The Structure of the Stems of Cordaites. Little was known 
about the structure of the stem until M. Grand 'Eury showed a few 
years ago that the tree described by Witham, under the name of 
Pinites Brandlingi, is really the stem of Cordaites. In the young 
state in this species the pith fills up the whole of the large medulla, 
but as growth proceeds, the pith not growing with the same rapidity 
as the surrounding tissue becomes transversely ruptured, resulting 
in the formation of a series of transverse lenticular cavities, forming 
a chambered pith. As growth continues the transverse diaphragms 
of pith get broken up, and eventually the pith cavity becomes an empty 
tube, except at its margin, to which cling annular rings of pith — the 
remains of the diaphragms which once extended across the cavity. 
Inorganic casts of these pith cavities are not uncommon, and are the 
fossils to which the names of Artisia or Sternbergia have been given 
{Artisia transversa Artis. sp., Plate LXV., fig. 6). Surrounding 
the pith in Cordaites (Pinites) Brandlingi is a zone of secondary 
wood, which consists of radially-arranged tracheides, separated by 
primary and secondary medullary rays, of one cell in thickness. 
The first-formed elements of the wood, the protoxylem, formed of 
narrow spiral tracheides, are followed by larger spiral tracheides; 
these are succeeded by scalariform tracheides, and then follow 
tracheides characterised by laterally-placed bordered pits with an 
oblique opening. It is this latter tissue which forms the bulk 
of the wood, to which additions are made from a cambium layer. 
The wood is enclosed by a thick cortex whose outer portion contains 
bands of dense, thick-walled fibrous tissue. The leaf-bundles which 
usually appear in pairs in transverse sections of the stem, before 
entering the leaf split up into numerous small strands, which pursue 
a parallel course through the leaf as already described. What are 
probably the roots of Cordaites have been described under the name 
of Amyelon. 
True, "annual rings" seem to be absent from Pinites or 
Araucarioxylon {Cordaites) stems, though specimens are occasionally 
met with where layers of feebly-developed wood are separated by 
broad bands of wood fibres of normal size. 
In Cordaites {Pinites) Brandlingi it is thus seen no primary 
wood occurs, the whole of the tracheides consisting of secondary wood. 
