66 ROYAL SOCIETY OF CANADA 
characteristic features of form and distribution belonging to the genus. 
In a radial distance of 15 mm., there is no evidence of growth 
rings beyond the occurrence of three vaguely defined zones in which the 
tracheids appear to have a somewhat shorter radial diameter. There 
is no such distinction as commonly relates to the differentiation of 
growth rings. A macroscopic examination of a band specimen shows 
that in a radial distance of 22 mm. eight apparent growth rings appear. 
These vary from 2-4 mm. in width, but their limits are poorly defined 
and they do not have the sharp terminations commonly met with in 
properly developed growth rings. A transparent section examined 
under a low power hand lens, shows no evidence of growth rings, from 
which we may infer that the appearances presented macroscopically, de- 
pend upon features which simulate rings only when taken collectively. 
This conforms exactly to what may be observed in modern Araucarias. 
The species thus agrees with the characters of the genus in the well de- 
fined absence of growth rings. 
In a radial section the elements of the protoxylem are seen to be 
narrow, spiral and scalariform structures which pass into tracheids with 
bordered pits by a series of gradations. The bordered pits on the radial 
walls of the tracheids are in 2-4 rows throughout. The medullary rays 
present the special differential feature of the species. The elements 
are of two kinds, parenchyma cells and tracheids. The parenchyma 
celis are usually equal to about three tracheids in length, and their 
lateral walls are too much decomposed to determine the number and 
character of the pits. The tracheids are usually long and narrow, in- 
terspersed ; and on their lateral, upper and lower walls bear numerous 
crowded and small bordered pits. This feature occurs in no other 
species brought under my notice, and it serves to differentiate C. 
Clarkii beyond all question. The further question arises as to whether 
this character is sufficient to separate the plant from the genus Cor- 
daites. All the other essential characters are those which belong to 
Cordaites, and the deviation indicated by the occurrence of ray tracheids 
is still such as may well come within the limits of the genus. This 
view finds its justification in the parallel case afforded by Abies, in 
which A. balsamea stands as a parallel exception to the rule that only 
parenchyma elements are present. 
In a tangential section (fig. 16), the rays are seen to be very variable 
in height as well as in their detailed structure. In some cases the rays 
are relatively broad celled and low, and more or less 2-seriate in part. 
In the higher rays the tracheids are at once distinguishable by their 
contracted form, and often greater height of the individual element. 

