74 MORPHOLOGY OF GYMNOSPERMS 



succession (fig. 59): (i) the outermost (lowest), a series of heavy, 

 imbricated bracts completely inclosing the structures within; (2) 

 next a series of the characteristic leaflike microsporophylls (10-20 

 in number); (3) on the top of the hemispherical receptacle, or on 

 the conelike tip of the axial one, a large number of remarkable ovulate 

 sporophylls intermixed with still more numerous sterile ones (" inter- 

 seminal scales"). The recorded length of the larger ovoid strobili 

 is 4 to 7 cm. ; while smaller ones (as those of Cycadella) range down 

 to I cm. 



A strobilus of this type, characterizing an extensively displayed 

 group of mesozoic gymnosperms, has tempted to much speculation 

 as to its relation to the flowers of angiosperms, which seem to have 

 begun to emerge into notice during the same time. Following 

 Wieland's original suggestion (22), Oliver (21), and Arber and 

 Parkin (24) have further elaborated the same thesis, and Scott (28) 

 has expressed the opinion that "the affinities between mesozoic 

 Cycadophyta and the angiosperms appear extremely significant," 

 and that it is "difficult to resist the conviction that the ancestry of 

 the angiosperms, so long shrouded in complete obscurity, is to be 

 sought among the great plexus of cycad-like plants which dominated 

 the flora of the world in mesozoic times." Oliver has suggested 

 angiocycads as the phyletic name of Bennettitales (or some allied 

 stock) as possible ancestors of angiosperms. Arber and Parkin 

 have analyzed the strobilus situation and given it a terminology. 

 An anthostrobilus is a bisporangiate strobilus in which the mega- 

 sporophylls are above the microsporophylls, as in Bennettitales and 

 all angiosperms. The earlier form of this strobilus is called the 

 proanthostrobilus, in which there is gymnospermy and the micro- 

 sporophylls have not reached the real stamen form; a definition 

 evidently constructed to describe the strobilus of Bennettitales. The 

 later form of anthostrobilus is the euanthostrobilus (or "flower"), 

 in which angiospermy has been attained and a well-marked perianth 

 has been developed. This phylogenetic suggestion further supposes 

 a hypothetical group of plants to intermediate between the Bennet- 

 titales (or their equivalents) and the angiosperms, to which the name 

 hemiangios perms is given. Ligneer (25) has dissented from this 

 view of the origin of angiosperms, for he regards the strobilus of 



