206 



MORPHOLOGY 



them a beaklike projection of the endosperm, a structure that char- 

 acterizes Ginkgo. No seeds have been found containing embryos ; and 



since the same fact is true of 

 the Cycadofilicales, it is evi- 

 dent that all the seed plants 

 of the Paleozoic shared this 

 peculiarity. 



Conclusions. A summary 

 of the characters of Cordaitales 

 shows an interesting combina- 

 tion. There are primitive 

 characters which indicate con- 

 nection with the Cycadofilicales 

 and the cycad line, such as the 

 large pith, the structure and 

 mesarch bundles of the leaf, 

 the structure of the ovule, and 

 the swimming sperms. The 

 advanced characters are the 

 lofty and branching habit, the 

 thick cylinder of secondary 

 wood, the form of the leaves, 

 and the compound ovulate 

 strobilus, all of which are char- 

 acters of the Coniferales. It 



FIG. 463. Section of ovulate strobilus of 

 one of the Cordaitales, showing the large over- 



FIG. 464. Pollen grains of one 



lapping bracts, in the axils of two of which there of the Cordaitales, showing the group 

 appear short branches bearing terminal ovules; of internal cells that probably belong 

 that to right also shows a bractlet. After to the male gametophyte. After 



RENAULT. 



RENAULT. 



seems evident, therefore, that the Cordaitales represent a second great 

 branch from the Cycadofilicales stock, a branch which leads towards 

 the Coniferales. This branch seems to have separated from the 

 Cycadofilicales long before the other branch which ends in the modern 

 Cycadales. 



