OF THE WOODY ZONE IN CALAMITE. 171 



ous wood_, that it is difficult to regard thetn otherwise than as 

 an elementary form of simple pleurenchyma^ or woody fibre. 

 But it is their elongated shape, the obliquity of their over- 

 lapping extremities, and their radiating disposition in the 

 transverse section which give them that character, and 

 not the existence of ligneous deposits in their interior. 



The conspicuous occurrence of these prosenchymatous 

 cells in a Calamite acquires additional interest from the 

 circumstance that they are identical with those already 

 described by Mr. Binney, under the name of " elongated 

 utricles,^^ as occurring in Sigillaria vascularis^ . In that 

 plant the outer of the two woody zones which the stem 

 contains is entirely composed of this peculiar tissue ; but 

 physiologically the fact deserves notice that, as Mr. Binney 

 points out, it gradually passes into the ordinary parenchyma 

 of the inner part of the stem. I may further observe 

 that small masses of the same tissue, also disposed towards 

 an arrangement in radiating lines, constitutes the external 

 ridges of the living Equisetum limosum and its allies. 

 Longitudinal strips, torn from the epiderm of that plant 

 and viewed from within, exhibit an alternate arrangement 

 of longitudinal bands that strikingly resembles what we 

 find in tangential sections of Calamites ; only the long 

 vascular tracts of the latter are wanting in the recent plant, 

 their place being occupied by cellular tissue. May we re- 

 gard this prosenchyma as a rudimentary form of pleuren- 

 chyma? Dr. Dawson refers to the same tissue under the 

 name of '' bast-tissue -/' but this term is only appropriate 

 to true pleurenchyma, and not to the more rudimentary 

 type under consideration. 



We may now inquire what are the true affinities of these 

 various forms of Calamites? Schimper, Carruthers, and 



* " A Description of some Fossil Plants, showing Structure, found in the 

 Lower Coal-seams of Lancashire and Yorkshire, by E. W. Binney, Esq., 

 F.E.S." Phil. Trans. 1865, p. 591. 



