300 CALAMITES. [CH. 



proposal which led to no little controvers3^ While retaining 

 the genus Calamites for such specimens as possess a thin bark 

 and a ribbed external surface, showing occasional branch-scars 

 at the nodes, and having such characters as warrant their 

 inclusion in the Equisetaceae, he proposes a second generic 

 name for other specimens which had hitherto been included in 

 Calamites. The fossils assigned to his new genus Galamo- 

 dendron are described as having a thick w^oody stem, and as 

 differing from Equisetum in their arborescent nature. Bron- 

 gniart's genus Galamodendron is made to include the plants for 

 which Cotta instituted the name Calamitea, and it is placed 

 among the Gymnosperms. This distinction between the Vas- 

 cular Cryptogam Calamites and the supposed Gymnosperm 

 Calamodendron is based on the presence of secondary wood in 

 the latter type of stem. The prominence formerly assigned to 

 the power of secondary thickening possessed by a plant as a 

 taxonomic feature, is now known to have been the result of 

 imperfect knowledge. The occurrence of a cambium layer and 

 the ability of a plant to increase in girth by the activity of a 

 definite meristem, is a feature which some recent Vascular 

 Cryptogams^ share with the higher plants: and in former 

 ages many of the Pteridophytes possessed this method of 

 growth in a striking degree. 



Although Brongniart's distinction between Calamites and 

 Calam,odendron has not been borne out by subsequent re- 

 searches, the latter term is still used as a convenient design- 

 nation for a special type of Calamitean structure. One of the 

 earliest accounts of the anatomy of Calamodendron stems is 

 by Mougeof'', who published figures and descriptions of two 

 species, Calamodendron striatum and C. histriatum. 



Some years later Gdppert^ who was one of the greatest of 

 the older palaeobotanists, instituted another genus, Arthro- 

 pitys'^, for certain specimens of silicified stems from the 

 Permian rocks of Chemnitz in Saxony, which Cotta had 

 previously placed in his genus Calamitea under the name of 



^ E.g. Isoetes, Botrychium, &c. ^ Mougeot (52). 



2 Goppert (64), p. 183. -» &pdpop, joint; irirvs, Pine-tree. 



