4 Johnstone, Calamites {Calamitind) varians, Stevjib. 



The Nodal Lines. In marked contrast to the nodal 

 constrictions of pith casts, the nodal line on the exterior 

 of this woody cylinder is a ridge, r {Plate), along the top 

 of which lies the chain of contiguous leaf-bases. The 

 protuberance is the highest part of a slight and gradual 

 bulging outwards of the upper internode of the two 

 involved. The leaf-scars are so placed on it that they 

 face slightly downwards as well as outwards, overhanging 

 the lower internode to the extent of about i mm. in some 

 places. At the branching nodes, the exact position of the 

 nodal line is obscure. 



Leaf-scars. Every node is furnished with its closely 

 packed whorl of leaf-bases, and this was probably true 

 also of the branch nodes. About twenty-five traces may 

 be counted on the flattened face of the fossil, and its whole 

 circumference must have produced at least fifty. Regard- 

 ing each of these as representative of a vascular bundle 

 of the axis, we should have in a woody cylinder, roughly 

 computed at 4 to 5 cms. in diameter, an approximation 

 of fifty proboxylem groups — not out of accord with the 

 evidence of structural sections. 



The scars of the leaves are elongated ellipses, I {Plate), 

 with their ends touching each other. By piecing together 

 the evidence of the best preserved scars, the following 

 details may be assigned to a typical trace when com- 

 plete : — 



{a) The boundary is a rather sharply outlined rim 

 which merges at the end of the oval with that of the 

 adjacent scar. The rim has the appearance of being 

 incomplete or broken down on its lower side. 



{b) A sloping internal face leading from the crest of 

 {a) gradually to the edge of 



{c) which is a minute circular pit almost like a pin- 

 prick. 



