A TYPE OF PALEOZOIC PLANTS. 397 



end of a small cast lying in a cavity, and from the upper 

 ends of some of the internodal ridges small sandstone 

 spokes radiate across the space, and abut on the enclosing 

 face of rock. These rays are simply the slender casts of 

 the infranodal canals, which have been preserved in an 

 unusually perfect form, while the woody tissue which 

 originally occupied the cavity has been entirely destroyed. 

 In addition to these subnodal scars, one occasionally 

 sees in the nodal region of a calamitean cast small dot-like 

 markings representing the place of origin of the leaf-trace 

 bundles ; also comparatively large circular depressions on 

 the nodal line ; these are the scars of branches. The late 

 Professor Weiss 1 of Berlin some time ago suggested a con- 

 venient classification of calamitean casts based on the 

 manner of occurrence of such branch scars. Corda, Dawes 

 and other earlier writers recognised that the specimens of 

 Calamites usually met with, were simply the casts of the 

 fistular pith cavity of the original stem. Williamson 

 brought out this point in a striking manner in the first of 

 his Royal Society memoirs, published in 1891. 2 Stur, in 

 his elaborate work on " Die Calamarien der Carbon-Flora 

 der Schatzlarer Schichten," describes, and figures several 

 silicifiel stems from Neu-Paka in Bohemia, in which the 

 true nature of the common casts is clearly demonstrated. 3 

 In some of these specimens a considerable thickness of 

 wood is preserved, the axis of the stem being occupied by 

 a cavity, the wall of which is formed by the inner face of 

 the wood. This central cavity is partially bridged across 

 at the nodes by the remains of a nodal diaphragm. A cast 

 made of this axial space gives an exact representation of 

 the ordinary calamitean fossil. The examination of sec- 

 tions of a Calamite stem with its woody tissue preserved, 

 shows that the inner face of the wood consists of projecting 

 blunt apices of xylem bundles, separated by broad medullary 

 rays of parenchyma. The thin- walled tissues of the latter 

 would decay more rapidly than the lignified tracheids of 



1 Weiss (2), p. 55. 2 Williamson (2). 



3 Stur, figs. 3-17, pp. 24-37. 



