6oo 
STRUCTURE AND LIFE HISTORIES 
619. Ancestors of the Angiosperms. Just as the 
Cycadofilicales indicate the ancestry of the cycads, so 
fossil types of Cycadophyta have been discovered which 
are interpreted by some paleobotanists as ancestors of the 
modern angiosperms. Other investigators, however, dis- 
sent from this view and consider that we have not yet 
(S.l)fl) 
FIG. 421. To the left, Cycadeoidea dacolensis Macbride. Longitudinal 
section of a silicified specimen of a bisporangiate cone (unexpanded flower), 
so taken that the pinnules of the microsporophylls on both sides of the 
central axis, or receptacle, are successively cut throughout their entire 
length. The lines indicate the planes of various sections through the cone, 
published in Wieland's "American Fossil Cycads." To the right Cycado- 
cephalus Sewardi Nathorst. Microsporangiate cone, natural size, preserved 
as an impression on a flat slab. From a fossil-bearing bed of the Trias, at 
Bjuf, Southern Sweden. (Left figure from Wieland, right figure from 
Nathorst.) 
sufficient knowledge of fossil forms to be justified in 
designating the ancestors of the Angiosperms. This 
difference of opinion is largely due to the meagerness of 
the available evidence. As one writer has stated it, 
"A trayful of flowers may be all the record of the Pterido- 
