304 CALAMITES. [CH. 



cells, with scattered secretory sacs. The increase in girth of the 

 central cylinder was often accompanied by a considerable 

 development of cortical periderm. The roots differed from the 

 shoots in having no carinal canals, and in the possession of a 

 solid pith and centripetally developed primary xylem groups 

 alternating with strands of phloem. 



The above incomplete diagnosis includes only some of the 

 more important structural features of the genus. Thanks to 

 the researches begun by the late Mr Binney of Manchester and 

 considerably extended by Carruthers, Williamson and later 

 investigators, we are now in a position to give a fairly complete 

 account of Catamites. The type of stem most frequently met 

 with in a petrified condition in the English rocks is that to 

 which Goppert applied the name Arthropitys, and it is this 

 subgenus that forms the subject of the following description. 

 Our knowledge of Calamitean anatomy is based on the exami- 

 nation of numerous fragments of petrified twigs and other 

 portions of different specific types of the genus. It is seldom 

 possible to differentiate specifically between the isolated 

 fragments of stems and branches which are met with in cal- 

 careous or siliceous nodules. As so frequently happens in fossil- 

 plant material, large specimens showing good surface features 

 and broken fragments with well-preserved internal structure 

 have to be dealt with separately. 



a. Stems. 



A transverse section of a young twig, such as is represented 

 in fig. 71, illustrates the chief characteristics of the primary 

 structure of a young branch of Calamites. The figure has been 

 drawn from a section originally described by Hick^ in 1894. 

 A very young Calamite twig bears an exceedingly close re- 

 semblance to the stem of a recent Equisetum, The axial region 

 of the stem may be occupied by parenchymatous cells, or the 

 absence of cells in the centre may indicate the beginning of the 

 gradual formation of the hollow pith, which is one of the 

 characteristics of Calamites. The student of petrified Palaeozoic 



1 Hick (94), PL ix. fig. 1. 



