THE PHYLOGEXY OP GYMXOSPERMS 169 



testimony of the majority of other structures, argues feebly for 

 recent community of origin. For example, we are compelled to 

 believe that so important a condition as heterospory was attained 

 independently by several lines. To put into the same genetic 

 group all heterosporous Pteridophytes would be regarded as a 

 morphological absurdity. If heterospory appeared independ- 

 ently in several lines, the same conclusion must be reached in 

 reference to its natural outcome, the seed, and the polyphyletic 

 origin of the Spermatophytes becomes extremely probable. A 

 corollary of the point last mentioned is that a living group may 

 not have a common phylogeny with any other living group show- 

 ing similar structures. For example, we are not necessarily re- 

 stricted to the heterosporous Pteridophytes in searching for the 

 ancestral forms of the Gymnosperms, for the latter may repre- 

 sent a distinct heterosporous line. While this increases the per- 

 plexities of phylogeny, it broadens its horizon, and homosporous 

 Pteridophytes may be included in the search for the origin of 

 the Gymnosperms. 



What seems to be a conspicuous error in many, schemes of 

 phylogeny is the tendency to focus attention upon very few 

 structures. It may be that the structures selected are the most 

 significant in a general way, but the organism is a plexus of 

 structures and must be considered in its totality. Very differ- 

 ent structures must have been laid hold of by the processes of 

 evolution, and it may not be possible to relate the resulting forms 

 properly upon the basis of any one or two structures. With all 

 of these uncertainties in mind, we may reach not a clear phylog- 

 eny of the Gymnosperms, but a clearer understanding of the com- 

 plexity of the problem and of the uncertainty of conclusions. 



Ever since Hofmeister's classic researches, it has seemed 

 clear that the Gynmosperms have been derived from Pterido- 

 phyte stock. As this view meets general consent there is no 

 need to discuss it. It was also natural for a time to regard 

 Gymnosperms as phylogenetically intermediate between Pter- 

 idophytes and Angiosperms, for it was not easy to believe that 

 such a structure as the seed could have appeared in more than 

 one genetic line. It is probably not going too far to say that 

 there is now no serious opposition to the view that the (rypiTiff- 

 sperm and Angiosperm lines are genetically independent. The 

 problem, therefore, has to do with the relation of the Gyinno- 



