156 PROF. W. C. WILLIAMSON ON THE STRUCTURE 



was preserved; but as the example only contained the 

 innermost portion of the woody zone, I put the subject 

 aside for a season, in the hope of meeting with further 

 illustrative specimens. 



Recently my attention has again been called to the subject 

 by a correspondence with M. Cyrille Grand-Eury, of St. 

 Etienne, who has obtained forms of Calamite altogether 

 different from mine. Other, apparently different, types are 

 in the possession of M. Adolphe Brongniart,of M. Schimper, 

 and of my friend Mr. Binney. It thus becomes probable 

 that several distinct forms of Calamites exist, and that a 

 large amount of combined labour will be required to elu- 

 cidate their varied aspects. Hence, though my present 

 researches have been chiefly directed to one portion of the 

 structure of one type, it appears desirable that what I 

 have ascertained respecting that type should be recorded 

 for the benefit of others labouring in the same field. 



The publication by Sir Charles Lyell of the figure referred 

 to has elicited various opinions respecting the fossil re- 

 presented. The conclusion at. which I arrived was, that 

 the central portion (a) was a cast of part of the pith from 

 the base of the plant ; that the verticils of radii (6), which 

 I would term verticillate medullary 7'adiij in contradistinc- 

 tion to medullary rays, were prolongations of the pith 

 passing through the woody zone to connect the pith 

 with the bark ; that c represented the woody zone of the 

 lowermost portion of the stem, whilst d represented the 

 exterior of a single articulation of the outer, or cortical 

 layer of the plant. 



But several difficulties opposed themselves to this ex- 

 planation. 1st. The supposition that any Calamodendron 

 consisted of two Calamites, one within the other, the one 

 representing the exterior of the pith, and the other the 

 exterior of the bark, was novel, and unsupported by other 

 testimony. 2nd. That the inner structure {a) and the 



