OF THE WOODY ZONE IN CALAMITE. 157 



outer articulation {d) could not belong to each other^ since 

 the former consisted of at least seven or eight internodes, 

 or joints^ whilst the outer structure {d) was a single joint. 

 It was therefore supposed by some that the central por- 

 tions [a, b, and c) represented the pith and ligneous zone 

 of one Calamite, which had been accidentally introduced 

 into the interior of the cast of another, when foreign 

 arenaceous material replaced the original vegetable tissues. 



In reply to these objections I would urge the following 

 arguments : — That the central pith {a) is a true Calamite 

 of the type of C. Suckoivii, Steinhauerii, and others, is un- 

 mistakable; that the medullary radii and investing lig- 

 neous zone belong to this pith is equally obvious, both the 

 latter facts being demonstrated by specimens to be described 

 in the following pages. The only doubtful point is the 

 relation which these inner structures bear to the supposed 

 bark {d, e) . Now, though the latter consists of one arti- 

 culation of about two inches in length, it does not follow 

 that it did not belong, like the central pith, to a portion 

 near the base of the stem, because we well know how 

 rapidly these nodes increase in size as we ascend from the 

 basal one. The aspect of the woody layer (c) demonstrates 

 that it has been prolonged considerably below the base of 

 the pith, or, in a word, that the pith has not extended so 

 far downwards as to reach the lowest articulations of the 

 stem; as if, reasoning from living exogenous types, we 

 might regard the latter portion as a pithless root rather 

 than a true stem. 



But even were these explanations not sufficient, there 

 yet remains another. The specimen shows that the car- 

 bonaceous matter of the ligneous zone (c) has been preserved 

 after the cellular structures of the medulla («) and of the 

 verticils of medullary radii {b) had been replaced by inor- 

 ganic sand. I deem it possible that the latter change may 

 have taken place before the woody substance of the supposed 



