CHAPTER XVII 

 CONIFEROPHYTES—GNETALES— EPHEDRA 



Professor Charles R. Barnes used to say that a character which 

 would make a species in the thallose jungermanias would make a 

 genus in the mosses. It seems to be a matter of taste whether the 

 Gnetales should be put into one family, with three genera, or into 

 three families, with one genus in each. All agree that there are only 

 three genera, Ephedra, Welwitschia, and Gnetum. Markgraf,^^' in 

 the second edition of Engler and Prantl's, Die natiirlichen 

 Pflanzenfamilien, makes three families, Ephedraceae, Welwitschia- 

 ceae, and Gnetaceae. Since the number of families seems to be a 

 matter of taste, we prefer to treat the assemblage, as most taxono- 

 mists treat it, under one family, the Gnetaceae. 



The characters which keep the three genera together in one order 

 and in one family are: vessels in the secondary wood; compound 

 strobilus in both male and female; the long micropylar tube formed 

 by the inner integument; opposite leaves; dicotyl embryos; no resin 

 canals. All of the Gnetales have all of these characters, although 

 some of them are not confined to this group. Many other gymno- 

 sperms have dicotyl embryos, most of them have a compound ovu- 

 late strobilus, many have opposite leaves, some have a more or less 

 elongated micropylar tube; but no other gymnosperms have this 

 combination of characters. The compound male strobilus and vessels 

 in the secondary wood are not found in other gymnosperms. The 

 combination of characters is sufficient to keep the three genera to- 

 gether, while the compound male strobilus and vessels in the second- 

 ary wood are sufhcient to separate them from the rest of the gymno- 

 sperms. 



Some of the characters belong to angiosperms as well as to Gne- 

 tales, and have tempted botanists to look upon the Gnetales as the 

 ancestors of the angiosperms. A strong objection to such a theory 

 of relationships is that no Gnetales have been found below the 

 Tertiary, while angiosperms were abundant in the Cretaceous, and 

 certainly existed in the Jurassic. 



361 



