86 KOYAL SOCIKTY ol" I ANAKA 



traiLsverso stt-tiou, renders it impossible to ascertain to wliat extent the 

 gTowtli rings ore (iihtinct, and reliance must, therefore, bo placed entirely 

 upon tho iiccuravy ol' the statement made. Iteferring more particularly 

 to the structure of C. lirandlingii, of which we fortuuatoly possess an 

 excellent specimen from St. Mtii-nne, and liicrefore typical, I lind tiiat 

 a v(M-y poorly dclined ring is ohservable, but it is to be uote<i tlmt such 

 rings (Fig. 1) are not of the nature of those conuiion to exogenous trees 

 of higher temperate or sub-arctic regions, but are more compar- 

 able witli those of sub-tropicial regions where there is a constant 

 tondentiy to continuous growth. Our ligure shows that the limits of 

 nnnual (?) growth are indicated l>y a very une(|iuil and narniw zone of 

 Iraclioids which dilTcr from tho.se on either side by their shorter ratliul 

 diameters. This feature is here of very uncertain vnliie. 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 triinsition into 

 oloincnts 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 wdiich is the outer face, were it not for the general 

 disposition of the vascular olcnu'nts. Tfcfcn-ing now to the various 

 species described by Dawsion,* ] lind that in two of his earliest he rcfons 

 to the obscurity of the growth rings, M'hile in three other cases he men- 

 tions them as distinct, and actually founds a species npon 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 stnu-tural features jiresented l)y the fossil, and 

 tJie sjinie is likewise tiue of 1). ouaugondianuni. In I), penneylvanicum, 

 which must be regarded as a true Cordnites 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. Tt 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 ol)soure rings displayed by C. Brandlingu 

 which finds its, parallel condition in the genus Araucaria. F'rom 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 

 ' Fobs. PI. of the Dev. & U. Sil. of Can., 1871. 12. 13. 



