Septkmbee 23, 1898.] 



SCIENCE. 



381 



entiation means that they had made a de- 

 cided departure, and we are probably able 

 to recognize only the most highly special- 

 ized forms. Of course, in what I have 

 said I may have been using the name Cor- 

 daites 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 de- 

 rived 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 

 Palffiozoic 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. If a 

 historical sequence can be established which 

 conforms to the views expressed here as to 

 the interrelationship of these lines the con- 

 clusion 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 recognize, 

 however, that the structures usually pre- 

 served are not the most convincing as to 

 relationships, and that nowhere are appear- 

 ances more deceitful. While we have no 

 sympathy with wild generalizations based 

 upon fragmentary material, there is an in- 

 creasing accumulation of data which fur- 

 nishes a substantial foundation for some 

 conclusions. It seems to be clear that dur- 



ing the Palseozoic there was an increasing 

 display of gymnosperms. The fragments 

 which bear this testimony became very 

 abundant in the later periods of the Palseo- 

 zoic, and are regarded, for the most part, 

 as Cordaites. Associated with these forms 

 is the great display of Marattia and its 

 allies. A distinct type of leaf and of stem 

 is attributed to each of these great groups, 

 and when seeds or sporangia are associated 

 with them the case seems clear enough, but 

 apart from such association the uncertainty 

 is profound. Intergrading forms between 

 the two are to be expected, but with material 

 so fragmentary and non-committal it would 

 be a rare chance that would lead to its 

 definite demonstration. In the Coal Meas- 

 ures the cycad type becomes apparent, but 

 not prominent. This would seem to indi- 

 cate either an early differentiation from the 

 Cordaites plexus or a late differentiation 

 from the Marattia plexus. I see no diffi- 

 culty in the former view, as I see no advan- 

 tage in multiplying the independent heter- 

 osporous and seed lines until forced to do so 

 by incontrovertible evidence. The domina- 

 tion of cycads during the Mesozoic and 

 their subsequent decline are well-known 

 facts. 



More suggestive, however, is the history 

 of the conifers. It is generally stated that 

 this line, in its modern expression, began 

 during the Palseozoic, and that our modern 

 genera have been recognized by stem and 

 leaf anatomy. Such methods of determi- 

 nation we know to be untrustworthy, as 

 there is the greatest possible amount of an- 

 atomical diversity even in contiguous re- 

 gions of the same organ, much more in dif- 

 ferent organs and at different ages. In 

 examining the claim that modern coniferous 

 genera appeared during the Coal Measures, 

 I find no evidence that seems to be worthy 

 of serious consideration excepting that with 

 reference to Ginkgo, and it is an interest- 

 ing fact that Ginkgo is no longer regarded 



