On the Calamites of the Coal-measures, 301 



of some Calamites, are the results of this peculiiir organization. In 

 one species of this Culatnopitus, instead of the longitudinal canals 

 of the woody wedges terminating at the nodes, they bifurcate, like 

 the wedges with which they are associated, and are continuously 

 prolonged from internode to internode. 



The ordinary structureless fossils found in shales and sandstones 

 receive a definite interpretation from the specimens described. The 

 fistular medullary cavities, due in the first instance, 9iot to decay of 

 the tissues, but to the rapid growth of the stem, became further en- 

 larged by the entire absorption of the true pith, which commenced 

 after the latter had fulfilled its purpose in the origination of the 

 woody wedges. This process terminated at an undulating line of 

 arrested absorption, the convexities of which projected outwards, 

 opposite the primary medullary rays, and inwards, oj)posite the 

 woody wedges ; and the inorganic cast of the cavity thus formed by a 

 physiological action constitutes the Calamites commonly seen in 

 collections. Hence they are not, like the Sternbergise, casts of a 

 cavity within a true pith, but their form represents that of the ex- 

 terior of the medullary tissue. The ridges and furrows of these 

 ititernal casts are not identical in position with the similar undula- 

 tions of the exterior of the woody zone, but alternate with them ; 

 so that the ligneous cylinder projects both externally and internally 

 where the woody wedges are located, and contracts, in like manner, 

 at the intermediate points opposite to the primary medullary rays. 

 The thin carbonaceous film which frequently invests these casts 

 is the residue of the altered elements of the woody zone, and pos- 

 sibly also of the bark, which latter has been very liable to become 

 detached from the former. The surface-markings of this carbona- 

 ceous film have usually no structural significance, being merely occa- 

 sioned by the impression of the hardened casts which they invest. 



Two kinds of branches are given off by Calamites — the one subter- 

 ranean, springing from peculiarly formed rhizomes, and the other 

 aerial, attached to the upright unbrauched stems. Tiie former of 

 these are of comparatively large size, the nodes from which they 

 have been detached being marked by large concave lenticular scars 

 as phragmata. These branches appear to have been given off from 

 central rhizomes in accordance with a regular phyllotaxis, but which 

 varied in different species. The aerial branches, on the other hand, 

 were merely slender apj)endages to a virtually unbrauched stem ; 

 they were arranged in verticils round the nodes, in variable num- 

 bers. Each branch sprang from the interior of one of the woody 

 wedges, the two halves of which were forced asunder to admit the 

 base of the ajjpendage, and from which its constituent vessels were 

 derived. The branch, deprived of its bark, never ajjjjcars to have 

 had a diameter equal that of two of the woody wedges ; and the rarity 

 of their occurrence attached to the stem seems to indicate that they 

 were deciduous. The l)ark investing them is not yet known, and the 

 exact nature of the foliage which they bore is also uncertain, owing 

 to discordant testimony respecting it ; but there appears no reason 

 for doubting that some of the verticillate Asterophyllites or Annu- 



