OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
483 
On turning from the internocles to the well-defined nodes of these Catamites, we dis- 
cover a series of very important modifications in the disposition of their tissues, altering 
many of their features. If a vertical section be made through the centre of the stem, we 
have the appearances presented at fig. 10, i, whilst fig. 2 represents the arrangement of 
the tissues in a tangential section made midway between the pith and the bark. 
The first feature which arrests attention in the vertical section is the material trans- 
verse enlargement of the woody zone (fig. 10, f) which takes place at the node (10, ij. 
This enlargement is both internal and external. In the former case the woody layer 
encroaches upon the pith, and in the latter upon the bark. The increment is due to 
the development of a considerable number of barred or reticulated vessels, but especially 
the former, which take their rise in contact with the outermost medullary cells above the 
node, and following an arching course across it, their concavities being directed towards 
the medulla, again terminate, as they arose from the medullary cells above the node, in 
those below it. It follows from this arrangement that only the outermost of these nodal 
vessels are prolonged across the internodes to the adjacent nodes above and below. 
In the transverse section we find, as the vertical one would lead us to expect, that the 
woody wedges at the nodes are much longer from their medullary to their cortical surfaces 
than at the internodes. The canals from which they respectively take their rise are either 
wholly wanting here, or so reduced in dimensions as to become quite inconspicuous. The 
large primary medullary rays (fig. l,c)have also become so restricted as in many cases to 
be scarcely traceable, bringing the wedges into very near contact, and rendering the resem- 
blance between the section and the similar one of an ordinary Coniferous Exogen still 
more close than in the case of the internodes. But the most striking peculiarity in the 
nodal arrangement of the tissues is seen in the tangential section (fig. 2, i). In the ex- 
ample represented in the Plate we have part of one node (?) and of two internodes (Jck). 
We now discover that each woody wedge, as it ascends to the node, divides into two por- 
tions, each of which bulges out somewhat, and which proceed obliquely upwards in a 
divergent manner to contribute their respective quotas to a corresponding but alternating 
series of wedges in the internode above. On magnifying one of these divergent por- 
tions (fig. 2, o) more highly, as is done in Plate XXIII. fig. 3, we discover that two 
changes have taken place compared with what was observed in the internodes: — 1st, 
the vessels (g) pursue a more undulatory and divergent course, leaving wider spaces 
between them ; and 2nd, those spaces (d) representing the secondary medullary rays, are 
occupied by irregular groups of cells which are very frequently arranged in double, and 
not unfrequently in threefold series. These sections also explain the almost complete 
disappearance of the primary medullary rays already noticed in describing the transverse 
section of this portion of the Calamite. 
But another very important feature occurs in these nodal parts of the organism. In 
fig. 2, two lenticular spaces (m) appear in the diverging portions of the woody wedges, 
and an examination of large series of specimens demonstrates that these spaces repre- 
sent branches. When the tangential section is made close to the pith, we find that the 
