256 PROF. W. C. WILLIAMSON ON A NEW FORM 



instead of terminating abruptly, tliey now proceed upwards 

 (fig. "] , e') parallel with the pith, forming the outermost 

 portion of the external longitudinal ridge of the axis. Un- 

 fortunately I possess no tangential section of this part of 

 the structure ; consequently I am unable to speak with 

 certainty respecting the superficial arrangement of these 

 vessels ; but a careful study of the various sections has led 

 me to the conclusion that there are two of these woody 

 bundles in each external rib of the axis. I believe that their 

 position in the transverse section is indicated by fig. 3 e, 

 or immediately external to each one of the longitudinal 

 canals, fig. 3 d — which accounts for their position at the 

 exterior of the ribs in the section fig. 5, c. If this ex- 

 planation be correct (and I have little doubt about it) , some 

 important inferences are suggested by the fact. It indi- 

 cates that these vascular bundles are the homologues of 

 the woody wedges of Calamites, and that the small canals 

 in like manner represent those of which, as Mr. Binney 

 and others have pointed out, one forms the innermost 

 angle or starting-point of each woody wedge. 



From each node we find the cellular tissue c descending 

 a short distance, but proceeding rapidly outwards to form 

 the upper part of the next inferior bractigerous disk. At h 

 we have the sporangiophore of the same disk, but forced in- 

 wards, away from its normal direction, to pass upwards 

 between the two sporangia i and /. It will be observed that 

 this upper surface of the bractigerous disk is very dififereut 

 from the lower one. In the latter, the gradually enlarged 

 ribs ascend from the centres of the internodes, like ten 

 buttresses, sustaining the disk with its sporangiophore and 

 mass of sporangia. On the other hand, at the upper 

 surface, the ribs, descending from the internode above, 

 are but slightly enlarged ; hence a slight concavity in the 

 disk is adapted to receive the inferior surface of the inner 

 sporangium /, which rests upon it. 



