COMPARATIVE ANATOMY OF GYMNOSPERMS 307 



as ancestral, because it occurs also in cycadean seedlings. The 

 foliar bundles of the Bennettitales were characterized by the 

 same peculiarities as those of the more modern Cycads. 



COKDAITALES 



On page 135 of the companion volume treating of Gymno- 

 sperms, the reproductive features and general morphology of 

 this interesting alliance are sufficiently described. The central 

 cylinder of the Cordaites enclosed a large pith, and was charac- 

 terized by considerable secondary growth. Like the Cycads and 

 unlike the Conifers of the present day, the secondary wood gen- 

 erally showed no annual rings. The wood of Cordaites, in some 

 cases at least, is to be identified with Araucarioxylon and Da- 

 doxylon, fossil woods which occur as far down in the strata as 

 the Devonian. Scott 14 has shown that in some species of 

 Araucarioxylon the primary wood of the stem was mesarch. 

 In a good many cases, however, the primary cauline bundles 

 of Cordaites are only distinguished by exceptionally large de- 

 velopment as compared with those of the higher living Gymno- 

 sperms. The leaf-traces were mesarch like those of the Cycads, 

 and Scott 15 compares the structure of a cordaitean leaf to that 

 of a pinna of Zamia. Fig. Ill, V, shows the structure of a 

 transverse section of part of a leaf of a species of Cordaites. 



The organization of the cauline and foliar bundles of the 

 Cordaites favors the view of their derivation from a pterido- 

 phytic ancestry quite as much as that of their reproductive 

 organs. Their well-marked foliar gaps and their large leaves 

 clearly indicate their filicinean affinities. The thickness of the 

 woody cvlinder and the freelv branching habit of the Cordaites 

 indicates a greater proximity to the Coniferales than to the 

 Cvcadales. 



GINKGOAT.ES 



The discovery of multiciliate sperms in Ginkgo is good evi- 

 dence for the antiquity and the affinities of the group. Still, 

 its pteridophytic features have suffered very considerable re- 

 duction as compared with the Cvcadales. Evidences of mesarch 

 structure are accordingly comparatively scanty. The bundles 

 of the stem are throughout endarch, and even the leaf-traces 

 show slight traces of the presence of centripetal wood. Wors- 



