OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
485 
and to speak of medullary rays in such examples, appears at the first glance to involve 
a misappropriation of terms. But, on the other hand, there is no doubt whatever that 
the woody zone which I have described is truly exogenous in its structure and mode of 
growth, though belonging to a Cryptogamic plant. Consequently we have in it the 
elements essential to the idea of one form of medullary ray. We have had, in the first 
instance, a cellular bud, within which vascular masses were developed ; and the portions 
of the primitive cellular tissue, connecting the inner cellular pith with the outer cellular 
layer, whether we call the latter bark or epiderm, are essentially the same things, so 
far as their genesis is concerned, in the Calamite and in a young Dicotyledonous shoot of 
the first year. The strong disposition shown by the cells of these structures in the 
Calamite to assume a mural arrangement confirms, though it is not necessary to, the 
idea of these organs being medullary rays ; and as these are the first of this class of 
organs that appeared in each young Calamite, I have applied to them the term usually 
employed by our best vegetable physiologists in such cases, viz. primary medullary rays. 
For similar and obvious reasons I assign to the rays separating the component laminae 
of the woody wedges the title of secondary medullary rays. They are formed subse- 
quently to the others, and, as in the case of Exogens, their number in the Calamite con- 
tinues to increase as long as the wedges containing them continue to grow. All the 
facts I have detailed justify the conclusion published in some of my previous memoirs, 
that in this woody zone of the Calamite we have a true exogenous growth ; whether we 
regard its intimate organization or its genesis, we are brought to this decision. There 
is a peculiarity in the exterior of this zone not to be overlooked. In his monograph 
already referred to, Mr. Binatey figures a decorticated stem, the decorticated exterior of 
which is marked by strong longitudinal ribs and furrows, with a thickened node. This 
configuration of the decorticated Calamite has been common to the type now under con- 
sideration, as shown in my restored figure 1. Though subject to considerable variations 
as to the degree of prominence, the transverse section always presents a more or less 
undulating outline, of which the exteriors of the woody wedges constitute the projecting 
portions. When we come to consider the nature of the arenaceous casts usually seen in 
geological collections, we shall find that the contour referred to forms an unfailing indi- 
cation whether any specimen under examination represents the exterior or the interior 
of the woody zone. 
The Longitudinal Canals. — M. Brongniart many years ago obtained some silicified 
stems of Calamites from the Coal-measures of Autun, which showed that the woody 
wedges took their rise from narrow pores or canals. Mr. Binxey has further demon- 
strated the same fact in his memoir, but was doubtful respecting their nature. He says 
that Dr. Hooker, “after carefully examining these openings, I believe, came to the con- 
clusion that they were passes for a peculiar kind of tissue which has unfortunately been 
destroyed, rather than the mere cavities which we now see in the specimens” (Joe. cit. 
p. 20). This supposition, however, is certainly not correct. We have the clearest evi- 
dence that these are true intercellular canals (Plate XXIV. fig. 11, e) running from node 
mdccclxxi. 3 x 
