OF THE CATAMITES OF THE COAL-MEASUEES. 
505 
vessels of the thickened woody zone in the same region of the Catamite ; but when we 
compare the two more minutely, we discover them to be very different things. AVe have 
seen that, in the fossil genus, the woody zone is materially thickened at each node by 
the addition of a number of arched vessels, which differ only in their increased numbers 
from those of the internodes. There is no change in the character of the individual 
vessels, nor interruption to the continuity of their course. The woody zone of the inter 
node gradually thickens into a lenticular form as it ascends to the node, and as gradually 
diminishes again as it enters the internode above. There is no abrupt termination or 
change in the vascular mass, neither is there any nodal diaphragm crossing it and inter- 
secting the course of the vessels ; but it is otherwise in all these points with the Equi- 
setums. Plate XXVIII. fig. 40 represents one of the coarsely spiral vessels (g) of fig. 41, 
taken from the point where it ascends from below, and enters the vascular mass (41, y). 
The ordinary spiral texture has already become yet more coarse and irregular (w), and 
this irregularity degenerates as the vessel increases in diameter into a large open network 
of lignine (x) deposited in the interior of the tube. Still higher the vessel is yet further 
enlarged, and now, forming part of the vascular mass (41, z), it is rendered angular by the 
pressure of other vessels like itself. Its angles ( z ) are here thickened by a continuous 
deposit of lignine, as in true scalariform vessels, and on its flat faces similar deposits occur 
in the form of minute and regular reticulations. AVe have nothing approaching to this 
condition in Catamites. AVe further discover in the node of the Equisetum that, in addi- 
tion to the cellular diaphragm, or extension of the pith that stretches across the fistular 
cavity, a still more dense layer exists, not only within the diaphragm, but which, as shown 
in fig. 41, is continued in a direct line across both the vascular and cortical zones ; at the 
exterior of the latter it merges in a second one (41, i ) at right angles to the first, and which 
separates the base of the branch (41, on) from the main stem. In both instances, as 
already shown, this dense layer truncates the vascular masses oj and z. The presence of 
this dense layer has perhaps something to do with one of the differences between the 
branches of Equisetums and Catamites, which in the former are very much more persis- 
tent than the deciduous ones of the latter appear to have been. I have shown that in 
the more matured stems of the Catamites the pith becomes wholly absorbed, which is 
not the case with the Equisetums. It may be urged that the reason for this difference 
lies in the fact that the stems of the former have been much more persistent than the 
annual growths of the latter. Such may be the case ; but the distinction holds equally 
good in the case of the permanent subterranean rhizomes of the Equisetums, where 
also the pith remains intact, not even becoming fistular. The existence of these rhizomes 
in both instances presents another feature of resemblance ; but as they occur equally in 
many other Cryptogams, e. g. the Marsileaceae, they have little definite value in rela- 
tion to the present argument. But this is not the case with the medullary rays that 
abound in the Calamites. Of course we should not expect to see the secondary ones 
represented in the Equisetums, because they do not possess the vascular laminae between 
which these structures are located ; but if the canals ( e , e ) of Plate XXIX. fig. 42 represent 
the similar ones in the Calamite, then the outward prolongation of the cellular pith (a) 
