CHAPTER XI 



GENERAL PHYLOGENY 



The results to which we are now brought are based entirely 

 upon developmental phases in anatomical elements of the vas- 

 cular cylinder. While our studies lead to certain definite con- 

 clusions, we do not in any sense regard these as final, but only 

 as affording one step in the solution of a question which must 

 be viewed not only from the broader standpoint of more extended 

 anatomical data but also from that of physiology as well, although 

 we feel disposed to insist that the final answer will be found to 

 rest chiefly upon an anatomical basis. That there may be room 

 for a different interpretation of the facts here recorded is quite 

 possible, since Dr. Jeffrey has recently permitted me to exam- 

 ine the manuscript of an important contribution to our knowl- 

 edge of the Abietineae, in which he brings out very significant 

 facts, which suggest that the group is of a much more primitive 

 character than has hitherto been supposed or than is indicated 

 by our own studies. It is therefore of importance that final 

 judgment should be suspended until the results of these various 

 studies, as well as those of Coulter, Chamberlain, and Ferguson, 

 all directed to the same end but prosecuted along somewhat 

 different lines, can be brought together and coordinated. It is 

 in this sense that the following conclusions are offered. 



In discussing the phylogeny of the higher gymnosperms 

 three subordinate phyla must be taken into consideration in the 

 following order: (i) Cordaitales, (2) Gingkoales, (3) Coniferales. 



Regarding the Cordaitales as the most primitive gymnosper- 

 mous stock of which we have present knowledge, it is possible to 

 trace its origin to the Cycadofilices. The genera Lyginodendron, 

 Heterangium, and Calamopitys present many structural features 

 which are common to all, and which not only establish their 



