20 



FOSSIL PLANTS. 



evidence of the cast of the outside of the central axis; but if the specimen were 

 fractured like No. 2, it would most probably in all respects be similar to that figured in 

 Plate I, fig. 2, as to the usual ribs, furrows, joints, and nodes so commonly found ou 

 ordinary Calamites. 



The wedge-shaped bundles of pseudo-vascular tissue originate from a small circular 

 orifice or opening, sometimes simple, as in the specimen now under consideration (Plate 

 II, fig. 2), but in other instances, apparently divided into several parts, as shown in the 

 annexed woodcut^ (fig. 3) ; they are composed of quadrangular tubes, arranged in radiating 



series, and increasing in size as they approach the circum- 

 ference. These tubes, but hexagonal in section, also extend in 

 an imperfect radiating series some distance from the "orifice" 

 towards the central axis, and increase in size as they approach 

 that point. They are divided by obhque dissepiments, and 

 their walls are much thicker than those found in the inner 

 woody cylinder of Sigillaria; and, instead of being covered 

 with fine transverse striae, both simple and anastomosing, 

 as in that genus of plants, they are marked by oval openings in the sides, horizontal 

 in the longitudinal section, Plate II, fig. 3, and termed by Dr. Dawson "reticu- 

 lated tissue." ' These openings are also shown, in a tangential section, in Plate II, 

 fig. 4, taken near the commencement of the wedges of pseudo-vascular tissue. The 

 diameters of the tubes increase gradually from their origin at the orifice, or opening, 

 to their termination at the outside of the cylinder^ where they are largest. The 

 number of these wedge-shaped bundles in this specimen (No. 1) is seventy-three, 

 alternating with an equal number of wedge-shaped masses of coarse and lax quad- 

 rangular tissue, having their broadest side next to the central axis, and diminishing 

 in size as they extend towards the circumference ; the size of the cells thus decreasing in 

 the opposite direction to that of the decrease of the tubes of the pseudo-vascular cylinder, 

 namely, from the central axis to the outside. These can be seen with the naked eye to 

 about yth of the distance from the central axis to the outside, where they cannot be 

 recognised without the aid of a microscope ; but tangential sections of- this part of the 

 pseudo-vascular cylinder show that it is traversed by bundles of tissue, oval in section 

 (Plate II, fig. 6) not much unlike in shape to those seen in Sigillaria vascularis, but with 



1 This cut is from a drawing made by Mr, Bone under the direction of Dr. J. D. Hooker, who 

 after carefully examining these openings, I believe, came to the conclusion 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. 



^ The openings in the walls of the tubes have a resemblance in shape to Dr. Dawson's left-hand 

 piece in fig. 67, pi. 12 (' Quart. Journ. Geol. Soc.,' vol. xxii) ; but the walls of the tubes in my specimens 

 are much thicker than those described by Dr. Dawson (op. cit., p. 140, 169). This structure, no doubt, 

 is familiar to all who have carefully examined under the microscope the charcoal in coal. 



Fig. 3. 



