104 THE MORPHOLOGY OF PTERIDOPHYTES 



the form genus Arthropitys, but common usage has extended 

 the apphcation of the name Calamites to include all methods 

 of preservation. The pith casts exhibit ridges and grooves, 

 corresponding in number to the protoxylem strands, run- 

 ning up the inside of the secondary wood and alternating at 

 successive nodes. In this respect they differ from Meso- 

 calamites, in which there was some variabiUty from node to 

 node, the ridges sometimes alternating and sometimes con- 

 tinuing straight across the nodes. A number of subgenera 

 are recognized which differed in their mode of branching 

 and, hence, in their general form. The subgenus Eucalamites 

 branched at every node. Fig. i6E is oi Eucalamites carinatus, 

 in which there were only two branches at each node, but 

 other species branched more profusely. By contrast, the sub- 

 genus Stylocalamites branched only near the top of the erect 

 organpipe-Hke trunk. 



Transverse sections of Calamites (Arthropitys) show very 

 little primary wood indeed, for secondary thickening pro- 

 vided most of the wood (Fig. i6H). The protoxylem was 

 represented by carinal canals and the small amount of 

 metaxylem present was entirely centrifugal. The wood rays 

 varied, according to species, dividing the secondary wood 

 into segments in some species, or losing their identity in a 

 continuous cylinder of wood in others. In all cases the wood 

 contained small wood-rays in addition, but otherwise was 

 composed entirely of tracheids with scalariform pitting or 

 with circular bordered pits on the radial walls. 



The leaves of Calamites were unbranched, with a single 

 mid-vein, and occurred in whorls of four to sixty. In most 

 species, they were free to the base, but in a few they showed 

 some degree of fusion into a sheath. They are placed in one 

 or other of two form genera, according to their overall 

 shape, Annularia being spathulate or deltoid (Fig. i6F), while 

 Asterophyllites were linear (Fig. i6G). The latter were 

 pecuHar in being heavily cutinized, with the stomata res- 

 tricted to the adaxial surface, suggesting that the branches 



