364 REMAINS OF STEMS OF DOUBTFUL AFFINITY, ETC. 



ness, due entirely to the compact massive secondary wood. Williamson J 

 has both described and figured them. The copiously branched roots 2 show 

 in the centre a triarch primary wood-strand, and next to this and all 

 around it is the secondary wood which is frequently excentric. In older 

 specimens concentric lines like rings of annual growth are plainly to be 

 seen in the secondary wood 3 , and these should be carefully examined, 

 because a true formation of yearly rings has never been observed in any 

 other remains from the Carboniferous formation, and would therefore be 

 particularly interesting. In other respects the wood shows little structural 

 peculiarity. It consists of a uniform mass of pitted tracheal elements, 

 and is traversed by a great many secondary rays, which are formed of a 

 single row of cells, and are often only one cell in depth. Two layers may 

 be distinguished in the thin rind. The inner layer consists of parenchyma 

 with no regular disposition of its cells, but the outer layer shows on the 

 transverse section nothing but short fusiform rows of cells thrust in between 

 one another, each row consisting of a large number of quite flat tabular 

 elements. It is obvious that each of these rows represents an original 

 parenchymatous mother-cell, in which a number of tangential divisions 

 were subsequently formed. 



1 Williamson (1), v, tt. 7-9. a Williamson (1), v, t. 7, f. 46. 



3 Williamson (1), v, t. 9, f. 56. 



