46 ROYAL SOCIETY OF CANADA 



the epithelium-cells are thick-walled and form a distinctly undulating 

 outline to the central passage or space. A separation of these three 

 genera then becomes possible, in the tirst instance, from the fact that in 

 Picea there is a total absence of resin-cells — a fact which serves to give 

 it direct connection with Pinus. Pseudotsuga is the most clearly defined 

 of all genera by reason of its spiral tracheids — a feature which serves to 

 differentiate it not only from Larix but from all other genera without 

 question. In cases of possible doubt, however, such as might arise through 

 the removal of the spirals by decay, it may be borne in mind that a fur- 

 ther differentiation appears in the large size of the resin-passages in the 

 fusiform rays of Larix. Avhile in Pseudotsiuja they are small and often 

 nearly closed. 



The genus Pinus stands by itself as a well-defined group which it is 

 impossible to confound with any other genus. As alreadj^ pointed out, it 

 possesses certain characteristics in common with Picea,- Larix and Pseudo- 

 tsuga, by reason of the presence of resin-passages and fusiform rays, as 

 also in the invariable presence of ray -tracheids. It is unique, however, 

 not only in the character of the fusiform rays, but in the nature of the 

 pits on the lateral walls of the ray-cells and in the structure of the cells 

 themselves. To these features ma}^ also be added the fact that the resin- 

 passages are large, always with thyloses, and the epithelium-cells are 

 thin-walled, forming an entire boundary to the central space. Within 

 its own limits, the genus presents certain well-defined differences, which 

 permit of its separation into two subordinate groups or subgenera. The 

 first of these divisions is distinguished by the presence of bordered pits on 

 the tangential walls of the summer wood, while the second is distinguished 

 by the entire absence of these elements. 



From the relations thus indicated, the various genera have been 

 arranged in such sequence as to exhibit as nearly as possible their true 

 genetic affinities, and the order given in the following synopsis may be 

 taken as expressing these relations in their principal aspects. I am fully 

 sensible, however, of the many imperfections which must enter into a 

 work of this nature— a work which is announced for the first time, and 

 has not yet gained that measure of solidity which can only come from its 

 actual application to the piirposes for which it is intended. It is, there- 

 fore, my hoj^e that those who may have occasion to use it will report any 

 serious deficiencies or point out any alterations which may tend to increase 

 its working efficiency. 



