258 PROF. W. C. WILLIAMSON ON THE 



centrale, un cylindre ligneux^ partage par de nombreux 

 rayons meduUaires tres regulierSj en faisceaux rayonnants^ 

 composes eux-memes de lames rayonnantes, de tissu 

 vasculaire strie, analogue h celui des Fougeres, des 

 Lepidodendron, des Sigillaria et des Stigmaria, et de tissu 

 plus fin^ sans stries ou ponctuations.-" 



As I shall show directly, this latter description includes 

 within M. Brongniart^s genus Calamodendron the group 

 of objects which for many years past I have demonstrated 

 to be true Equisetiform Calamites, but which M. Brong- 

 niart thus unites with objects which he believed to be 

 dicotyledonous Gymnosperms. I may observe here that 

 M. Brongniart had no conception of the existence of an 

 enormous number of Carboniferous Cryptogams which 

 possess largely developed, exogenous, vascular or xylem 

 zones within their cortical layers ; he believed such a 

 combination to be impossible ; therefore the fact that a 

 plant possessed such a zone was to him, as it has long 

 been to some of his disciples, a clear proof that it could 

 not possibly be a Cryptogam. 



In 1869 1 published, in the ' Transactions of the Literary 

 and Philosophical Society of Manchester'"^, a memoir 

 '^ On the Structure of the Woody Zone of an undescribed 

 form of Calamite,'' in which I demonstrated the existence 

 of an exogenous woody zone, and also I arrived at the 

 conclusion, '' that the Calamites constitute essentially one 

 large group of plants, with some considerable range of 

 variation in the details of their internal organization " [loc. 

 cit. p. 179). This conclusion, as might be expected, was 

 rejected by many who had been trained in the school of 

 Brongniart. A few remain who still reject it. 



Like myself, M. Goppert obtained specimens of Cala- 

 mites with distinct, exogenously developed, vascular zones, 



* Vol. iv,, 3rcl ser. 



