OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
479 
distinct concentric layers of tissues, a central pith, surrounded by a ligneous zone, which 
in its turn was invested by a thick cortical or epidermal cellular structure. The pith 
(Plate XXIII. fig. 1, b *), cellular and solid in the very young growths, very soon became 
fistular in the older internodes (1 a). The woody zone surrounding the pith closely 
resembled, in its organization, the first year’s shoot of a recent Conifer. It consisted of 
numerous woody wedges (1/ ), each one starting at its inner extremity from a narrow 
canal (1 e). These wedges were separated from each other by peculiar prolongations 
of the pith (1 c), to which I would assign the name of primary medullary rays; whilst 
secondary medullary rays separated the constituent vascular laminae of each wedge, as in 
recent Exogens. These wedges, with their intervening primary medullary rays, extended 
vertically in straight lines from node (1 i) to node. At each of the latter points they 
underwent an entire rearrangement to be described in detail. Investing the woody 
cylinder was a thick, cellular, cortical layer, in which I have failed to discover any traces 
of vessels. At each node the cellular pith extended across the entire medullary area, so 
that the fistular interior of the stem consisted of a linear series of oblong chambers, 
each one of which corresponded with an entire internode, and was separated from its 
neighbours by the several transverse medullary diaphragms referred to. 
Having thus indicated the general features of the most common type of Calamite, we 
may now proceed to a more detailed examination of the different varieties that I have 
obtained. The sections represented by the figures from 2 to 10 inclusive belong, I 
believe, to one variety, though they were not all prepared from the same specimen. 
This also appears to be the most common form, since a large proportion of the examples 
which I have examined belong to it. Its various tissues may be described in the order 
of their superposition, beginning at the centre. 
The Pith . — This invariably consists of the common type of cellular parenchyma, 
though the forms which the cells assume vary according to the direction followed in 
making the section. When cut transversely (Plate XXIV. fig. 9, b) they exhibit the 
ordinary hexagonal form, though their sides are usually somewhat unequal ; and in this 
section there is no approach to any linear arrangement, such as we find in the vertical 
sections (Plate XXIII. fig. 8 & Plate XXIV. fig. 10, b). In the latter we almost inva- 
riably find the cells elongated vertically. This is especially the case with the innermost 
ones, and with those (Plate XXIV. fig. 11 ,b) forming the inner wall of the longitudinal 
canals hereafter to be noticed. We also observe that they are arranged in linear vertical 
rows, their parallel faces being constantly at the upper and lower ends of each cell. The 
narrow transverse diameters often seen in the innermost of these medullary cells (as in 
fig. 8, //) do not constitute a primary condition, but are the result of physiological changes 
to be described. Fig. 10 represents a vertical section through the centre of a node (?), 
and two internodes (Jc). It exhibits the two large fistular cavities of the latter [a, a) filled 
* This figure is an attempted restoration of part of a stem including one node and part of two internodes, 
portions of the cortical layer and of the woody zone being removed so as to reveal the external Calamitean surface 
of the pith b. 
3 u 2 
