7o8 THE AMERICAN NATURAUST. [\'ol. XXXVIII. 



examine the manuscript of an important contribution to our 

 knowledge of the Abeitineae, in which he brings out very signifi- 

 cant facts suggestive of the idea that this 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 and Chamber- 

 lain, all directed to the same end but prosecuted along entirely 

 distinct lines, can be brought together and co-ordinated. It is in 

 this sense, therefore, that we offer the following. 



Summary and General Conclusions. 



In discussing the phylogeny of the higher Gymnosperms, 

 three subordinate phyla must be taken into consideration in the 

 following order :—(i) Cordaitales, (2) Ginkgoales, (3) Conife- 



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 Lyginoden- 

 dron, Heterangium, Calamopitys and Pityoxylon present many 

 structural features which are common to all, and which not only 

 establish their relation to the Cycadean line of descent, but they 

 offer many suggestions of that course of development which is 

 realized in the higher Coniferales. They, therefore constitute 

 the real starting point for two lines of descent, the first of which 

 embraces the Cycadales. With this w^e have little or nothing to 

 do at the present moment, beyond establishing its probable rela- 

 tion to the other gymnosperms. The second line emerges in a 

 type of plants having characteristics distinctly allied to those of 

 the Coniferas, and it is this line of descent with which we are 

 now chiefly concerned. It is now possible to define the origin 

 of this phylum somewhat more exactly than Coulter has done 

 (7 & 8), since there is good reason to believe that it emerges 

 from the Cycadofilices through Poroxylon. Scott (52, P- 39^) 

 has already pointed out the relations of this genus to the Cyca- 

 dofilices and the Cycadacea^ on the one hand, and to Cordaites 

 on the other, so clearly as to remove the necessity for detailed 



