90 



G. B. Wieland — American Fossil Gycads. 



mens shows it to have been far advanced in the Trias. It 

 indeed suggests 1 an evolutionary process that may well have 

 been the most significant of all that went on amongst the plants 

 of the early Mesozoic forests. 



Even in the Cycadeoidean side line reduction of flowers from 



primitive crowns had proceeded 

 Fig. 11. well beyond the mere limits of 



floral size in the Angiosperms, 

 and the conviction grows that 

 such changes were the identical 

 ones responsible for the advent 

 of these now dominant plants. 

 Twelve years ago this seemed 

 the first probability. To-day it 

 is a theory undergoing demon- 

 stration, whether we regard the 

 Angiosperms as monophyletic or. 

 as seems vastly more reasonable 

 in the light of the once dominant 

 cycadophytan plexus, poly phyletic. 

 Cosmopolitan and plastic races, 

 already ancient of lineage, are 

 better conceived of as moving 

 forward en masse with little loss 

 in diversity of features. 



Regarding the general outlines 

 of such an evolutionary course, 

 fair inferences were possible with 

 Gycadeoidea alone well known. 

 That this type had an ancestry in 

 which spiral insertion of leafy fer- 

 tile organs on a main axis was as 

 distinct as in the female Gyeas 

 was obvious. And that these 

 organs were of strictly Cycadalean 

 nature appeared likewise evident 

 before the restoration of Wel- 

 trichia, equally balanced in its 

 characters between Cycadaceans 

 and Cycadeoideans, or perchance 

 even representing one of those 

 long occulted Medullosans. But 

 with this form before us we know, 

 in fine, that the more or less dis- 

 tinctly monaxial insertion of fer- 

 tile organs was long retained, that 

 the whorl of stamens with disk growth early appeared, and 

 that concomitant floral reduction and branch formation were 

 at least in part late. 



Fig. 11. 



Cycadeoidea turrita. 

 x 25. 



Mature seed containing em- 

 bryo cut in nearly the true 

 median plane showing the mi- 

 cropylar tube of three layers, 

 a heavy inner palisaded, a thin 

 middle, and a lighter outer pal- 

 isaded layer, — the tube interior 

 being filled with a soft tissue. 

 Two of the five to six wings of 

 the "blow off" appear. These 

 are the smallest mature seeds 

 of Cycadeoidea so far known. 



