CHAPTER LII. 



GNETALES. 



I. Recent. 



In this group of Gymnosperms are included three genera, 

 Ephedra, Gnetum, and Welwitschia. They differ widely from one 

 another in vegetative features, and Ephedra, the most primitive, 

 is distinguished by certain important peculiarities of the repro- 

 ductive organs. 



Ephedroideae. Ephedra. 

 Gnetoideae. Gnetum, Welwitschia. 



Having regard to our exceedingly meagre knowledge of fossil 

 representatives, it is unnecessary to deal fully with the recent 

 types^, but the members of this aberrant section of seed-plants 

 exhibit morphological characters of interest from the point of 

 view of comparison with the Bennettitales and the Angiosperms. 

 Though in external appearance the three genera are poles asunder, 

 they have in common certain features both in the vegetative and 

 reproductive organs which differentiate them from all other 

 Gymnosperms and connect them more closely than the Cycads or 

 Conifers with the Angiosperms. The leaves are opposite; the 

 secondary xylem contains vessels in addition to tracheids; the 

 male and female flowers are characterised by the possession of one 

 or two envelopes in addition to the usual single integument; the 

 inflorescences, occasionally though not as a rule bisporangiate^, are 

 distinguished by a dichasial system of branching, a character 

 foreign to Gymnosperms as a whole though exhibited by the stem 

 of Wielandiella, a member of the Bennettitales. There are good 

 reasons for believing that pollination is effected by insects^ in 



^ For a general account of the group, with illustrations, the student is referred 

 to Wettstein (11) and Lotsy (11), or to Coulter and Chamberlain (10). 



2 Land (04); Berridge and Sanday (07) p. 127; Lotsy (11) p. 293. 



3 Pearson (06^) p. 274; (09) p. 343; Berridge and Sanday (07) p. 172; Karsten 

 (92); Porsch (10). 



