BS ROYAL SOCIETY OF CANADA 



In relation to the spiral tracheids, the uniseriate rays are unques- 

 tionably secondary in development, as their reduction from the mul- 

 tiseriate form common to the lower Gymnosperms, and so conspicu- 

 ously developed in the Cycads, has followed the reduction of spirals 

 tc bordered pits, and they are, therefore, to be held in general, as 

 evidence of a higher type of development. 



Resin Cells. — The non-resinous wood of the Taxaceœ constitutes 

 a well defined means of separating this family from the Coniferœ in 

 which the resin is a prominent feature. In this latter family, the 

 resin is always derived from specialized structures of a more or less 

 complicated nature. These are resin cells and resin passages, and 

 the two may be discussed separately. 



The resin cells in transverse section are to be distinguished by 

 the presence of resinous contents, or by the colour which they naturally 

 possess; and where the plane of section passes sufficiently near to the 

 terminal wall, the latter is seen to have the general aspect of a sieve 

 plate. It is upon this latter feature that one is sometimes obliged to 

 rely exclusively, as in Abies, Larix and Tsuga, although certain features 

 of form and relation to adjacent elements, may assist in the final deter- 

 mination. The resin cells are variously distributed in different genera, 

 being rarely grouped, and these differences may be utilized as differ- 

 ential characters though of subordinate value, inasmuch as there is no 

 sharply defined variation, but one form may readily occur in another 

 genus to which it does not strictly belong. 



In longitudinal section the resin cells are seen to be long- 

 cylindrical with square terminations (Figs, 24, 25 and 29). The length 

 is very variable in different species and so far, there seems to be no 

 specific relation between length and either genus or species, a view 

 which is strengthened by the observation that even in the same species, 

 notable variations occur according to situation, as to whether in the 

 spring or the summer wood (Figs. 24&, c and 25a, &). Thus, in Sequoia 

 gigantea (Fig. 25a, V) the cells from the spring wood which contain 

 an abundance of resin, are less than two-thirds the length of those 

 from the summer wood which contain little or no resin. Also in 

 S. sempervirens, a similar difference occurs, only that the cells from 

 the spring wood are less than half those from the summer wood. And 

 so for all other genera. The cells commonly bear simple pits on the 

 radial walls, but in Sequoia sempervirens these sometimes show transi- 

 tions into bordered pits (Fig. 24c), and it commonly happens that in 

 the summer wood the cells lie immediately internal to tracheids with 

 square ends and bordered pits (Fig. 24c), or they may even fall within 

 the same series as in Abies amabilis (Fig. 29a, h), where a is coterminous 

 with & at its upper end. In these genera, which normally have no 



