GENERAL PHYLOGENY 157 



type of development. With respect to the precise position of 

 Sequoia in particular, its relation to Abies on the one hand, and 

 to such genera as Thuya and Cupressus on the other, cannot be 

 taken, in the present state of our knowledge, to indicate its origin 

 from or its ancestry to either of them. The facts derived from 

 anatomy, however, do indicate a more or less common origin for all 

 four genera, and from this point of view, taking into account the 

 peculiar features exhibited by Sequoia, they would seem to justify 

 the idea that that genus represents a short side line of develop- 

 ment, which does not lead to the evolution of other types, but 

 terminates in S. gigantea after a comparatively brief period. The 

 sequence of species for each genus cannot always be determined 

 with a full measure of satisfaction, and these difficulties may pos- 

 sibly be made clear by reference to the succession of the two 

 species of Sequoia, which is difficult to determine on purely ana- 

 tomical grounds, but the general tendency of the facts already 

 recited is to give to S. sempervirens the more primitive posi- 

 tion, --a view which is sustained by its paleontological history. 

 The relations brought out in the foregoing studies, and the 

 reasons for the conclusions reached, may be made more obvious, 

 without the tedious method of a detailed discussion, by refer- 

 ence to the accompanying table of anatomical data (Appendix A), 

 which substantially summarizes all the results derived from the 

 study of particular structures. In preparing this table the various 

 anatomical features have been chosen with reference to (i) the 

 constancy of their occurrence, (2) their structural prominence, 

 and (3) their obvious relation to diagnostic purposes. In their 

 horizontal extension an attempt has been made to arrange them 

 in accordance with the law of frequency, as well as with reference 

 to their relation to development, in such wise that while the spiral 

 tracheid is assumed to be the most primitive type of the vascular 

 structure, the presence of two kinds of cells in the medullary ray 

 may be held to express the highest form of development. To 

 the members of the series so constituted we may then assign 

 arbitrary values in arithmetical sequence from one to seventeen; 

 while those subordinate characters which are represented by 



