372 THE ANATOMY OF WOODY PLANTS 



In accordance with the hypothesis of the derivation of the 

 angiosperms from the Bennettitales, a relationship between this 

 cycadean group and the Gnetales has been suggested. There 

 seem to be very slight grounds for this assumption of affinities. 

 The so-called "pollen chamber" of Ephedra is not morphologically 

 equivalent to the pollen chamber of the lower gymnosperms 

 which is derived by the breaking down of cells in the lysigenous 

 manner, and in this respect is in marked contrast to the depression 

 on the apex of the nucellus of Ephedra, which is continuously 

 covered with the epidermis. Moreover, Ephedra and the other 

 Gnetales are siphonogamous in contrast to the zoidogamous 

 condition of fertilization in the Cycadales. The details of organ- 

 ization of such a flower-like structure as is found in Welwitschia 

 apparently supplies no adequate basis for comparison with the 

 bisporangiate strobilus of the Bennettitales. The original error of 

 Saporta in designating the impressions of the fructifications of 

 bennettitean types as belonging to hypothetical proangiosperms 

 or primitive angiosperms has manifested a considerable degree of 

 vitality in the rather long interval since it was first advanced; 

 but there seems little reason to accept it at the present time, in 

 view of our increased knowledge of the organization of both vege- 

 tative and reproductive parts in the various groups of seed plants, 

 living or extinct. 



The Gnetales are clearly gymnosperms which in certain features 

 of anatomical structure and reproductive organization have made 

 a marked advance in the direction of the characteristics of the 

 angiosperms, and it is not improbable that they are at least a 

 cognate group. They present, however, no valid resemblances 

 in either their reproductive or their vegetative parts which justify 

 an assumption of relationship, even remote, with the extinct 

 bennettitean Cycadales. It therefore appears highly unlikely 

 that either the angiosperms or the Gnetales have any close degree 

 of relationship with any archigymnospermous group, although 

 it seems not at all improbable that they are somewhat closely 

 related to one another. 



