THE BASIS OF THE STEM STRUCTURE. 189 



at the same results as myself, but from data derived from a 

 study of the external characters. ^ 



With respect to the genus Cupressus, as now constituted, it 

 may be pointed out that it is separable into two distinct groups, 

 the first of which may be designated as Chamaecyparis, and the 

 second as Cupressus proper.^ The distinguishing feature of 

 the first section is to be found in the character of the pits 

 on the tangential walls of the summer tracheids, which are 

 narrowly lenticular and not very large. The second section 

 embraces all the remaining species which have heretofore been 

 recognized under this genus. The distinguishing feature is 

 found in the conspicuously large and broadly lenticular pits 

 on the tangential walls of the summer tracheids. 



Taxodium and Sequoia approach one another closely in the 

 fact that the pits on the lateral walls of the ray cells are con- 

 spicuously bordered, while the same element also serves as the 

 basis of specific distinction. Thus in Taxodium the pits are 

 round and the orifice? is narrowly oblong, the border, therefore, 

 broad; while in Sequoia the pits are distinctly oval or elliptical 

 and the orifice broadly oblong, the border thus becoming much 

 narrower and sometimes even obscure. These differences are 

 very well defined and constant, and admit of no doubt as to the 

 particular genus. Both of these genera approach Juniperus in 

 the presence of prominent resin cells, as well as in the fact that 

 these elements are disposed in tangential bands. To this must 

 also be added the fact, already pointed out, that a further affinity 

 is based upon the occurrence in all three, of bordered pits on 

 the lateral walls of the ray cells and similarity of structure in 

 the terminal walls of the ray cells. The occurrence of occa- 

 sional resin passages in Sequoia sempervirens and a similar 

 occurrence of imperfectly formed resin passages in Abies 

 nobilis point to the fact that there is a strong point of contact 

 between these two srenera. 



The relation between Sequoia and Abies, thus indicated, is 

 greatly strengthened in other ways, as in the absence of resin 



^Journal Linn. Soc, XXI, 312. 



2 Dr. Masters' results again accord with my own in the subdivision of the 

 genus Cupressus, although on anatomical grounds I prefer to reverse the order. 



