538 STUDIES IN FOSSIL BOTANY 



the male flower consists of a stalk bearing two pollen- 

 sacs, each of which is considered to represent a sessile 

 stamen. In Ephedra the arrangement is similar, but 

 the sessile stamens vary in number, according to the 

 species, from two to eight, and each consists of two 

 pollen-sacs. The Gnetaceae, however, are a highly 

 modified group, as to the geological history of which 

 we have no certain information. We must be cautious 

 in using their morphology (which in itself is none too 

 clear) to explain that of an ancient family like the 

 Cordaiteae, which is known to have existed as far back 

 as the Devonian period. If, as has recently been 

 suggested, the flowers of the Gnetaceae are reductions 

 from a much more complex type like that of the 

 Bennettiteae (see Chap. XIII.) it is clear that the 

 family can have only the most remote affinity with 

 the Cordaiteae. 1 



M. Renault's summary of the morphological con- 

 ditions in the male Cordaianthus certainly has the merit 

 of simplicity. He says : — " In the midst of sterile 

 bracts arose one or more fertile bracts, the filament of 

 which, scarcely modified, bore at its summit three or 

 four sacs containing the pollen." 2 On this view, the 

 stamens would in no case be axillary structures, but 

 would represent so many sporophylls, interspersed 

 among sterile bracts. We might compare each stamen 

 to that of Ginkgo ; in the latter the pollen-sacs are 

 usually only two in number, though stamens with three 

 or four sacs sometimes occur, and are pendulous instead 



1 See Arber and Parkin, " Studies on the Evolution of the Angiosperms : 

 the Relationship of the Angiosperms to the Gnetales," Ann. of Bot. vol. 

 xxii. July 1908, and the papers there cited. 



2 Renault, Tiges de la flora carbonifire, p. 308. 



