36 STUDIES IN FOSSIL BOTANY 



under Dicotyledons. Consequently, Brongniart was led 

 to divide the Calamites into two groups : those which 

 he supposed had no secondary growth, and which he 

 therefore left under the old generic name of Calamites ; 

 and those which had such growth. The latter he trans- 

 ferred to Phanerogams, founding the genus Calamo- 

 dendron for their reception. 1 Calamodendron was 

 subsequently subdivided by Goppert into Arthropitys, 

 with simple medullary rays, and Calamodendron proper, 

 with the more complex structure which I have just 

 described. 



There is at present no evidence remaining that any 

 Calamarian plant was without secondary growth. The 

 Calamites supposed to be without secondary thickening 

 have turned out to be simply medullary casts, from 

 which the surrounding tissues have partly or wholly 

 perished. The specimens with their structure preserved 

 invariably possess secondary tissues, the only exceptions 

 being excessively young twigs, and even these often show 

 the commencement of the cambial growth (see Fig. 5). 

 At present the evidence is that all Calamites, so far as 

 they are known to us, formed secondary wood and bast, 

 and consequently this distinction of Brongniart's falls 

 to the ground. We may therefore go back to the old 

 name Calamites, using it as synonymous with the 

 Arthropitys of the French authors, and retaining the 

 genus Calamodendron in Goppert's restricted sense. 



Another type of Calamarian stem is represented by 

 Calamites petty curensis, already referred to (p. 24). It 



1 See Brongniart, Tableau dcs genres de vigitmix fossiles, Paris, 1849, 

 pp. 47-50. Brongniart was also influenced by the occurrence of seeds 

 among the branches of Asterophyllites, which he regarded as the foliage of 

 Calamodendron. 



