172 



MORPHOLOGY OF SPERMATOPHYTES 



During the Carboniferous, also, forms appeared which seem to 

 be referable distinctly to Ginkgoales, a line which in its begin- 

 nings has seemed hard to distinguish from certain of the Cor- 

 daitales. Ginkgo has always been peculiar in its combination 

 of Cycad and Conifer characters, and this may be accounted for 

 by its early origin in connection with the Cycadofilices and Cor- 

 claitales. 



During the Mesozoic there appeared the Bennettitales and 

 Cycadales, the former making much the greater display. It 

 is reasonable to suppose that these two lines were derived either 

 independently or together from the Paleozoic Cycadofilices. 



The historic evidence concerning the Coniferales is most 

 indefinite and uncertain. The group, as we understand it to- 

 day, is relatively modern, but there is no evidence as to the rela- 

 tive ages of the two great lines, Taxaceae and Pinaceae, which 

 compose it. For a long time the genus Araucaria has been 

 regarded as the most ancient representative of the Conifers, but 

 this idea seems to have arisen from the Araucaria-like wood 

 which is so abundant in the Paleozoic, which has proved to be- 

 long to the Cordaitales. Just which of the Conifer lines is 

 the most ancient remains for future investigation to discover; 

 that the line as a whole was an offshoot from the Cordaitales 

 seems to us most probable. In fact, the Cordaitales, as ordi- 

 narily recognized in the Carboniferous, 

 seem to us to be forms well on their way 

 toward the Coniferales. 



In reference to Gnetales, there 

 seems to be absolutely no historic evi- 

 dence, and morphology is equally at 

 fault. That the three genera now ex- 

 isting are a fragmentary representation 

 of some ancient line seems to be a rea- 

 sonable conclusion; and the characters 

 are related so distinctly to those of other 

 Gymnosperms that it seems hardly a 



question but that the group has the same origin, although one can 

 not venture upon any more detailed hypothesis. 



In order to summarize clearly the statements made above, 

 the accompanying diagram is introduced, but it must be inter- 

 preted in a most general sense. 



