298 CALAMITES. [CH. 



the family Equisetaceae. Lindley and Hutton^ give several 

 figures of Calamites in their Fossil flora, but do not commit 

 themselves to an Equisetaceous affinity. 



An important advance was made in 1835 by Cotta^, a 

 German writer, who gave a short account of the internal 

 structure of some Calamite stems, which he referred to a new 

 genus Calamitea. The British Museum collection includes some 

 silicified fragments of the stems figured and described by Cotta 

 in his Dendrolithen. Some of the specimens described by this 

 author as examples of Calamitea have since been recognised as 

 members of another family. 



In 1840 Unger^ published a note on the structure and 

 affinities of Calamites, and expressed his belief in the close 

 relationship of the Palaeozoic plant and recent Horse-tails. 



An important contribution to our knowledge of Calamites 

 was supplied by Petzholdt'' in 1841. His main contention was 

 the Equisetaceous character of this Palaeozoic genus. The 

 external resemblance between Calamite casts and Equisetam 

 stems had long been recognised, but after Cotta's account of 

 the internal structure it was believed that the apparent 

 relation between Equisetum and Calamites was not confirmed 

 by the facts of anatomy. Petzholdt based his conclusions on 

 certain partially preserved Permian stems from Plauenscher 

 Grund, near Dresden. Although his account of the fossils is 

 not accurate his general conclusions are correct. The speci- 

 mens described by Petzholdt differ from the common Calamite 

 casts in having some carbonised remnants of cortical and woody 

 tissue. A transverse section of one of the Plauenscher Grund 

 fossils is shown in fig. 70. The irregular black patches were 

 described by Petzholdt as portions of cortical tissue, while he 

 regarded the spaces as marking the position of canals like the 

 vallecular canals in an Equisetum. Our more complete know- 

 ledge of the structure of a Calamite stem enables us to 



1 Lindley andHutton (31). 



2 Cotta (50). I am indebted to Prof. Stenzel of Breslau for calling my 

 attention to the fact that Cotta's work appeared in 1832, but in 1850 the same 

 work was sold with a new title-page bearing this date. 



^ Unger (40). ^ Petzholdt (41). 



