56 ROYAL SOCIETY OF CANADA 
transverse section, renders it impossible to ascertain to what extent the 
growth rings are distinct, and reliance must, therefore, be placed entirely 
upon the accuracy of the statement made. Referring more particularly 
to the structure of C. Brandlingii, of which we fortunately possess an 
excellent specimen from St. Etienne, and therefore typical, I find that 
a very poorly defined ring is observable, but it is to be noted that such 
rings (Fig. 1) are not of the nature of those common to exogenous trees 
of higher temperate or sub-arctic regions, but are more compar- 
able with those of sub-tropical regions where there is a constant 
tendency to continuous growth. Our figure shows that the limits of 
annual (?) growth are indicated by a very unequal and narrow zone of 
tracheids which differ from those on either side by their shorter radial 
diameters. ‘This feature is here of very uncertain value, and in par- 
ticular regions of the zone it becomes almost obliterated. The zone it- 
self is not more than a few tracheids wide, and the transition into 
elements of the surrounding structure takes place so gradually, both in- 
wardly and outwardly, that it would be quite impossible to determine 
which is the inner or which is the outer face, were it not for the general 
disposition of the vascular elements. Referring now to the various 
species described by Dawson,’ I find that in two of his earliest he refers 
to the obscurity of the growth rings, while in three other cases he men- 
tions them as distinct, and actually founds a species upon their presence 
(D. annulatum). But as appears from the specific diagnosis of this 
species elsewhere in this paper, this statement is based upon a complete 
misinterpretation of the structural features presented by the fossil, and 
the same is likewise true of D. ouangondianum. In D. pennsylvanicum, 
which must be regarded as a true Cordaites according to our present 
limitations, growth rings are present and of the general type common to 
trees of high temperate regions. The summer wood is very narrow, 
consisting of two to four rows of radially flattened, squarish elements. 
The termination, and consequent demarcation from the spring wood of 
the following year, is quite abrupt, the whole appearance being much 
like that which may be found in some of the living species of Cupressus 
or Thuya. It is thus true that of all the species originally described by 
Dawson, only one of them shows well defined growth rings. The others 
all conform to that type of obscure rings displayed by C. Brandlingii 
which finds its parallel condition in the genus Araucaria. From these 
considerations it becomes apparent that the descriptions borrowed from 
author to author without verification, and appearing in the most recent 
revisions of the genus, are in great need of being recast with respect to a 

1 Foss. Pl. of the Dev. & U. Sil. of Can., 1871, 12, 13. 

