Ch. XXIV.] 



CALAMITES. 



365 



Calamites cannot belong to the Equiseta, nor probably to any tribe of 

 flowerless plants. He conceives that they are more nearly allied to the 

 Gymnospermous Dycotyledons. They possessed a central pith, surround- 

 ed by a ligneous cylinder, which was divided by regular medullary rays. 

 This cylinder was surrounded in turn by a thick bark. Of fossil stems 

 having this structure Brongniart formed his genus Calamodendron, which 

 includes many species referred by Cotta, Petzholdt, and Unger, to the 

 genus Calamitea. The Calamodendron is described as smooth exter- 

 nally, its pith being articulated and marked with deep external vertical 

 striae, agreeing, in short, with what geologists commonly call a Calamite. 

 Since the appearance of Brongniart's essay, Mr. E. W. Binney has made 

 many important discoveries on the same subject ; and Mr. J. S. Dawes 

 has published (Quart. Journ. Geol. Soc. Lond. 1851, vol. vii. p. 196) a 



more complete account of this sin- 

 g " 4,a gular fossil. Their views have been 



confirmed by Prof. Williamson of 

 Manchester, who has communicated 

 to me a specimen, figured in the 

 annexed cut (fig. 478), in which 

 we see an internal pith answering 

 in character to the Calamodendron, 

 and yet having outside of it another 

 jointed cylinder vertically grooved 

 on its outer surface, so that in the 

 same stem we have one calamite 

 enveloping another. Yet that they 

 both formed part of the same plant, 

 is proved by the following circum- 

 stances : — 1st. Near each articula- 

 tion of the pith, radiating spokes 



Portion of a Calamite, near the base, showing the , ' _ „„ i „i _''+__+_ 



external cylinder, connected by radiating vessels are seen to proceed and penetrate 



with the cast of the pith. Its position inverted n p K'jmpnm ?nnp One corrmlete 



to allow the light to enter the cavity. lne "gneOUS zone. KJUV complete 



Communicated by Prof. W.O. Williamson. w h or i or C [ YC \ Q f t h ese ra( Jii j s 



visible in the annexed figure near the bottom of the hollow cavity, whilst 

 another and superior whorl is incomplete ; several radii, corresponding 

 to the first, remaining, while the rest have been broken away, their place 

 being shown by scars which they have left. 2dly.- In addition to these 

 whorls, called medullary by Prof. Williamson, there are seen in other 

 specimens a set of true or ordinary medullary rays. 3dly. The woody 

 zone, penetrated both by the spoke-like vessels beforementioned and by 

 the medullary rays, is usually reduced to brown carbonaceous matter, 

 preserving merely a tendency to break in longitudinal slips, but in some 

 specimens its fibrous tissue is retained, and resembles that of Dadoxylon. 

 4thly. Outside of this zone again is another cylinder, supposed to have 

 been originally a thick cellular bark, nearly equal to one-third of the 

 whole stem in diameter, grooved and jointed externally like the pith. 



