CYCADOFILICALES AND CYCADALES 303 



The Mesozoic Cycadales are ordinarily grouped under the 

 heading Bennettitales on account of the remarkable features pre- 

 sented by their reproductive structures, which are very different 

 from those exemplified by any living Cycadales. The uniting of 

 both microsporophylls and megasporophylls in the same strobilus 

 is a frequent feature of this group and has been considered by some 

 to indicate an affinity with the angiosperms, particularly as the 

 ovuliferous sporophylls are shut in by a panoply provided by the 

 swollen apices of so-called interseminal scales sterile structures 

 interposed among the fertile ones. The question of the possible 

 descent of the angiosperms from the Bennettitales is one which 

 can scarcely be considered seriously from the anatomical standpoint, 

 since there is practically nothing in common in the anatomical 

 organization of the two groups, either in the reproductive or in 

 the vegetative features. The fructifications of the Bennettitales 

 before their real affinities were known were attributed by the 

 distinguished French paleobotanist Saporta to a group which he 

 designated as proangiosperms. Now that their actual relation- 

 ships are known, there seems scarcely any reason for regarding 

 them as allied to the angiosperms. The Bennettitales supply an 

 excellent illustration of the relative conservatism of anatomical 

 structures, for, although they present marked differences in repro- 

 ductive features from the Cycadales, their vegetative anatomy 

 does not differ in any important particular from that of the modern 

 group. 



If the anatomical situation for the Cycadales in the large 

 sense be summarized, it becomes clear on the basis of the general 

 canons of comparative anatomy elucidated in earlier pages of 

 the present volume that they exhibit strong filicinean features. 

 The anatomical examination of the foliar strands reveals crypto- 

 gamic or centripetal wood and in some cases concentric organiza- 

 tion. The evidence derived from the consideration of the anatomy 

 of the leaf is confirmed in a number of instances by the organiza- 

 tion of the strands of xylem in the reproductive axis. The testi- 

 mony of the conservative parts leads to the assumption of the 

 former presence of centripetal xylem and concentric fibrovascular 

 strands in the vegetative stem. The general result reached on 



