A YORKSHIRE NATURALIST 199 



mart's hands, one an equisetiform Calamite, and the 

 other a lycopodiaceous Sigillaria, in each of which 

 the internal structure was preserved. In one of 

 these plants was found a central pith surrounded by 

 an exogenously developed cylinder of wood. In the 

 Sigillaria a similar condition existed. These woody 

 zones were unquestionably formed by true cambium 

 layers. Brongniart then believed that no living 

 Cryptogam possessed a cambium ; hence he con- 

 cluded that both the Calamite and the Sigillaria must 

 be removed from the positions in which he had 

 originally placed them amongst the Cryptogams, 

 and he classed them both with the Conifers and 

 Cycads, believing them to be gymnospermous plants. 

 This error has led to nearly thirty years of conflict 

 amongst palseo-botanists. 



In 1832 a new specimen was obtained by the 

 late William Vernon Harcourt, of York. It was 

 a fragment of a branch of a Lepidodendron, a 

 lycopodiaceous genus, in which much of the in- 

 ternal organisation was beautifully preserved. 

 After being described in England, first by Mr. 

 Witham, of Lartington, and subsequently by the 

 authors of the " Fossil Flora of Great Britain," a 

 section of it was obtained by M. Brongniart, and 

 carefully described by him. This was one of those 

 Lepidodendra which do not develop their woody 

 cylinder until an advanced period of growth. Hence, 

 notwithstanding the many existing features of close 

 identity between Sigillaria and Lepidodendron, Brong- 



