OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
513 
their murications, b, have now become tubular. Fig. 47, which represents one of the 
spines of fig. 46, exhibits this condition more distinctly. The murications on the 
surface, a, have had their extremities broken off, consequently we can look through 
the circular apertures thus left, into the interior of the hollow spine. We further see, 
at ci', that these murications are now developing into tubular secondary extensions of 
the primary cavity of the spine : a feature to which further attention will be drawn. 
Within the capsule-wall, fig. 45, a, we again find the inner membrane, f distended by 
large cells, g. These latter now touch one another, though their mutual pressure has 
not been sufficient to interfere with their spherical form. These cells now average 
•0025 in diameter. The plastic investment reappears as before at e. 
Fig. 46 is a section of a crushed specimen in which both the capsule-wall, a, and 
the spines, b, now become brittle, are broken up into innumerable sharply-defined frag¬ 
ments, b'. These brittle spines all display the tubular form of murication represented 
in fig. 47. But the most curious feature of this section is furnished by its inner layers 
of membrane. We have a structureless one at / splitting into two layers at /', the 
innermost of the two laminae uniting with a yet more internal one, f". This latter 
is covered with numerous closely-grouped circles. A more enlarged representation of a 
portion of this innermost membrane is given at fig. 48. The rings are now seen to 
be circular prominences, /, the summit, /', of each of which is a little depressed and 
circumscribed by a sharply-defined circular groove,/". 
Figs. 43, 44, and 49 throw light upon each other. Fig. 43 represents the surface 
of a portion of the capsule-wall, as seen under a comparatively low power, exhibiting 
the bases of numerous spines. When the microscope is so focussed that we obtain an 
optical section at a plane corresponding to the external surface of the fragment, we 
merely see the transverse sections of the hollow cylindrical spines, as at b, b, but on 
increasing the magnifying power and bringing a more internal surface of the fragment 
into focus we obtain the effects seen in fig. 44, which represents the upper left-hand 
portion of fig. 43, enlarged 650 diameters. We now see that at their bases, a', a', the 
cavities of several spines appear to open into one another. , But this arrangement is 
explained by the segment of a transverse section of a Traquaria, fig. 49. We here 
observe that not only are the lower extremities of the spines enlarged, as already 
described, but that they frequently spread out (fig. 49, a", a"') like the roots of a tree, 
covering areas many times wider than the maximum diameter of the spine. Fig 49 
only exhibits such of these outspread roots as run in the plane of the section ; but at 
a, a, a, we have transverse sections of other similar roots which spread out at right 
angles to that plane, and which interlace and often appear to anastomose with other 
similar ones. It is this ramification of the bases of the tubular spines that occasions 
the numerous irregular circular and semi-circular areolations visible in the capsule-wall 
in such sections as figs. 40, a, and 41, a, a'. A considerable portion of the inner sur¬ 
face of fig. 43 is covered with a very irregular and ill-defined reticulation.* In fig. 49 
the free ends of the spines subdivide into large branches. 
* Explained in some supplementary observations on p. 533. 
