432 GYMNOSPERMS 



juvenile leaves, we should place last. On the whole, we believe in the 

 recapitulation theory, but we feel certain that it has been called upon 

 to explain things for which it is not responsible. 



From time to time we have stated or assumed that, in some way 

 or other, the gymnosperms have come from the pteridophytes, and 

 most botanists will agree to this theory. Wettstein,''^° a profound 

 student of phylogeny, says that the gymnosperms represent a plant 

 type which is traceable to the pteridophytes, by way of the Cycado- 

 filicales. He thinks that the unity of the entire group is not such as 

 to indicate the remnant of a former race, but rather, a terminal 

 series going back to a common ancestry. 



Wettstein's view is accepted by most botanists. Both cycado- 

 phytes and coniferophytes show an unmistakable pteridophyte 

 ancestry. Have they arisen independently, or has one of them given 

 rise to the other? If both have come from a common ancestor, the 

 coniferophytes have progressed much farther and retain fewer of the 

 ancestral characters. As far as any evidence from fossils is concerned 

 the groups were never any more related than they are now. 



In some way or other the Cordaitales, the lowest of the conifero- 

 phyte stock, came from the pteridophytes. Then the Cordaitales 

 gave rise to the Coniferales and probably also to the Ginkgoales. 



Long after the Cordaitales became differentiated from the pteri- 

 dophyte stock, the Bennettitales and Cycadales arose, independent- 

 ly, from the Cycadofilicales. The cycadophyte line is much more 

 homogenous than the coniferophyte, and, in our opinion, there is no 

 doubt that it arose from the Filicales. 



The coniferophyte line is not so homogeneous. Those who lay 

 great stress upon the leaf gap and use the terms "lycopsida" and 

 "pteropsida," insist that the coniferophyte line must have come from 

 the Cycadofilicales, or at least from the Filicales, because all belong 

 to the pteropsida. Others would minimize the value of the leaf gap 

 in determining relationships, and say that lycopods do not have leaf 

 gaps because the bundles are exarch and the leaf traces, being con- 

 nected with the protoxylcm, are already at the periphery of the 

 stele, and naturally would not produce gaps. The lycopods, as a 

 group, have comparatively small leaves, with entire margins, and, 

 in this respect, bear a much closer resemblance to the coniferophytes, 



