1898 ] THE ORIGIN OF GYMNOSPERMS 159 
finds its modern expression in the conifers. In the acknowledged 
Cordaites, therefore, I recognize a transition region between the 
homosporous-eusporangiate plexus of Filicales and the more 
modern conifer series; while in the cycads we have a line which 
continued more of the fern habit and structure, recognizable not 
merely in its foliage leaves and general port, but in its occasional 
vascular bundles of concentric type, and its multiciliate sperma- 
tozoids. The Cordaites, however, must have included forms that 
we have not recognized as such, for it is only when they become 
differentiated from the fern habit that in the main we are able 
to distinguish them. This very fact of their sharp differentiation 
means that they had made a decided departure, and we are prob- 
ably able to recognize only the most highly specialized forms. Of 
course, in what I have said I may have been using the name 
Cordaites in a much more inclusive sense than taxonomy would 
justify. As ordinarily defined I would see in them the first dis- 
tinct beginnings of a type which afterwards gave rise to the 
conifers; as used in this paper, they refer to a plexus of forms 
derived from the homosporous-eusporangiate Filicales which gave 
rise to both cycads and conifers as divergent lines, one retaining 
more nearly the fern habit and structure and culminating earlier, 
the other departing more widely from the habit and structure 
and culminating later. I believe that some Paleozoic forms 
now regarded as ferns will be found to be more closely related 
to the Cordaites. How many other lines arose from this large 
Cordaites plexus, as I have defined it, we have no means of 
knowing, but it seems to be responsible at least for all of the 
living gymnosperm forms. 
It is important to obtain such historical evidence as we can 
in reference to the gymnosperm lines, restricted in this paper 
to the Cordaites, conifers, and cycads. Ifa historical sequence 
can be established which conforms to the views expressed here 
as to the interrelationship of these lines, the conclusion will 
have additional support. I need not apologize for the paucity 
of data furnished by paleobotanists. They have done what they 
could, and we are greatly in their debt. Morphologists recog- 
