EQUISETITES. 



57 



the Intel-nodes of this form have long proved a difficulty, several 

 authors having regarded them as branch - scars occurring some 

 distance above the nodal region. Lindley compared them with the 

 nodal septa of Calamites, and Schimper afterwards regarded them 

 as displaced nodal diaphragms. This is, I believe, the correct 

 explanation of the circular discs. 



FIG. 3. Equisetiteg columnaris, Brongn. [No. 40,561.] 

 (Block lent by the Cambridge University Press.) 



The frequent occurrence of isolated nodal diaphragms renders it 

 probable that the tissue of these organs was strengthened by the 

 development of periderm, and possibly by a subsequent sclerification 

 of the cells. It has been shown J that the parenchymatous nodal 



1 Williamson & Scott (94), p. 889. 



