PHYLOGENY 433 



in which the small leaf, with entire margin, is dominant. Of course, 

 some gymnosperms, notably the Cordaitales, have large leaves; 

 and in some, like Ginkgo, the margin is not entire. But there are 

 no big compound leaves, like those of the Cycadofilicales. Cones 

 were already highly developed in the lycopods, long before they 

 appeared in the cycadophyte line, and they appeared in the Cor- 

 daitales long before they appeared in any of the cycadophyte 

 phylum. 



As far back as they can be traced, the lycopod and fern phyla 

 seem to be just as distinct as they are now. Throughout our long 

 association in teaching and in conducting research, the late Dr. 

 John M. Coulter and myself, relying chiefly upon the importance 

 of the leaf gap, assumed that the coniferophyte line has come from 

 the Cycadofilicales. As the survivor of the pair, if I were still in 

 active teaching, I should still teach that theory, but the teaching 

 would lack the dogmatic confidence which characterized the earlier 

 days. So let us assume, but with minds still open, that the Cordai- 

 tales have come, directly or indirectly, from ferns. 



The major problems which remain concern the origin of the Coni- 

 ferales, Ginkgoales, and Gnetales. 



The Gnetales, like Minerva, seem to have sprung, full armed, 

 from the head of Jove; but it is possible that the discovery of some 

 new group, like the Caytoniales, may prepare the way for a less 

 fanciful theory of origin. On the other hand, it is possible that thor- 

 ough investigations of complete life-histories in the lower dicots, 

 especially trees, will help to place the Gnetales where they really 

 belong. 



For a long time the Ginkgoales were classed with the Taxaceae. 

 When motile sperms were discovered. Ginkgo was removed from 

 the taxads, and made the sole living representative of an order. The 

 leaves and long stalks of the female flowers are also characteristic of 

 the new order. The mere fact that the sperms are ciHated does not 

 seem sufficient to warrant a new order. In its early development, 

 the sperm is almost identical with that of Jimiperus, and Juniperus 

 usually has a dense mass of kinoplasm, which may represent a bleph- 

 aroplast. There seems little doubt that the sperms of Jimiperus 

 are descended rather recently, phylogenetically, from motile sperms; 



