X] CALAMITES. 303 



pith of a stem either originally fistular or rendered hollow by 

 decay. The investigation of the internal structure confirmed 

 this view, and proved that the surface-features of a Calamite 

 stem do not represent the external markings of the original 

 plant, but the form of the inner face of the cylinder of wood. 

 The ribs represent the medullary rays of the original stem or 

 branch, and the intervening grooves mark the position of the 

 strands of xylem which are arranged in a ring round a large 

 hollow pith' 



With this brief preliminary account we may pass to a 

 detailed description of the anatomical characters of Calamites. 

 The genus Calamites may be briefly defined as follows : — 

 Arborescent plants reaching a height of several meters, 

 and having a diameter of proportional size. In habit of 

 growth the Calamites bore a close resemblance to Equisetum ; 

 an underground rhizome giving off lateral branches and erect 

 aerial shoots bearing branches, either in whorls from regularly 

 recurring branch-bearing nodes, or two or three from each 

 node ; and in some cases the stems bore occasional branches 

 from widely separated nodes. The leaves were disposed in 

 whorls either as star-shaped verticils on slender foliage shoots, 

 or in the form of a circle of long narrow leaves on the node of a 

 thicker branch. Adventitious roots were developed from the 

 nodal regions of underground and aerial stems. The cones had 

 the form of long and narrow strobili consisting of a central axis 

 bearing whorls of sterile and fertile appendages ; the latter in 

 the form of sporangiophores bearing groups of sporangia. The 

 strobili were heterosporous in some cases, isosporous in others. 

 The stems had a large hollow pith bridged across by a 

 transverse diaphragm at the nodes in the centre of the single 

 stele; the latter consisted of a ring of collateral bundles 

 separated from one another by primary medullary rays. Each 

 group of xylem was composed of spiral, annular, scalariform and 

 occasionally reticulate tracheids, the position of the protoxylem 

 being marked by a longitudinal carinal canal. The shoots and 

 roots grew in thickness by means of a regular cambium layer. 

 The cortex consisted of parenchymatous and sclerenchymatous 



1 Vide p. 310. 



