360 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



an ancient and diversified group which unfortunately has not been 

 certainly recognized in the older fossil floras — Gnetopsis of the Car- 

 boniferous (Stephanian) of Europe and North America being, ac- 

 cording to Oliver and Salisbury, a pteridosperm related to Conostoma. 

 Gnetum has been definitely recognized in the Pliocene of Holland, 

 while several species of Ephedrites have been recorded from the 

 Jurassic, Cretaceous, and Tertiary. The relationship of these latter 

 can not, however, be regarded as established beyond suspicion. 

 Leaves suggestive of Gnetum are also present in the Lower Cre- 

 taceous of Virginia. 



The chief point of interest in the Gnetales is their angiospermous 

 characters shown in their possession of true vessels (absent in all 

 other gymnosperms) in their broad rays, the presence of companion 

 cells in the bast, the incipient perianth of the inflorescence, the floral 

 morphology, the details of sporogenesis, fertilization, and embry- 

 ogeny with the elimination of archegonia, the organization of eggs, 

 and the dicotyledonous embryos. Such of these features as were 

 known to the older morphologists suggested that the Gnetales were 

 to be looked upon as representing the progenitors of the flowering 

 plants and this view, which has long been in disrepute, has recently 

 come into prominence again and is supported by a considerable body 

 of evidence. Lang and Thompson have shown that the Gnetales are 

 undoubtedly related to the rest of the gymnosperms and are not to 

 be considered true angiosperms, as Lignier advocated. On the other 

 hand, the attempt to consider them as a reduction series from the 

 Mesozoic Cycadeoidales must be considered an abortive speculation. 

 Some light on their geological history is greatly to be desired, since 

 the most recent work with the existing forms indicates an ancient 

 and collateral relationship with the balance of the Coniferophyta, 

 going back possibly to the same pteridosperm plexus from which the 

 Cordaitales took their origin. Hence, comparisons of the gnetalean 

 flower with the fructifications of existing conifers is obviously futile. 

 In the other direction, the least aberrant genus, Gnetum, while in no 

 sense a " missing link," furnishes good grounds for considering an as 

 yet unknown group of gnetalean forms as the ancestors of the angio- 

 sperms through the primitive amentiferous families. 



The members of the order Taxales are dioecious and they differ 

 from all other Coniferophytes except the Ginkgoales and Gnetales, 

 in that true cones are not organized, the ovules developing into 

 seeds with a partially fleshy testa (aril) or cupule. Normally only 

 a single ovule of the sporOphyll reaches maturity in the modern 

 forms, alt hough more seem to have been developed in extinct genera 

 like Palissya. 



The Taxales contain but 8 of the 36 existing genera of the 

 Coniferophytes and only about 75 of the 325 existing species. At 



