BENNETTITALES 59 



PHYLOGENY 



Paleobotanists agree that the Bennettitales have come from the 

 CycadofiHcales. The leaves of some of the lower forms, like Ptilo- 

 phyllum and Williamsonia, are so identical with the leaves of Dioon, 

 that the similarity may not be accidental. It may mean that both 

 Bennettitales and Cycadales inherited the leaf from some very re- 

 mote ancestor; or it may be possible that some of the unattached 

 leaves actually belong to the Cycadales. The habit of the trunk in 

 both groups may have been similarly inherited. But the strobilus is 

 so different in the two lines that the Bennettitales could not have 

 given rise to the Cycadales. The lateral leaflets of the megasporo- 

 phyll, entirely lost in the earHest known Bennettitales, could not 

 have been transmitted to the Cycadales. The vertebrate paleontolo- 

 gist illustrates this law of evolution by saying that a tooth, lost in 

 phylogeny, is lost for good. The Bennettitales came from the Cyca- 

 dofiHcales, probably in the later Carboniferous. Although no defi- 

 nitely recognizable material dates that far back, the first recogniza- 

 ble specimens are so advanced that they must have been separated 

 from the main line for a long time. 



That the Bennettitales may have given rise to any of the angio- 

 sperms we regard as not only improbable but impossible. One at- 

 tempt to connect them makes the connection with the Sympetalae, 

 a group obviously derived from the Archichlamydeae, and not only 

 cycHc, but tetracychc. A more recent attempt to connect them with 

 the angiosperms, and a connection which seems more reasonable, has 

 been with the magnolias; but, again, the superficial resemblance of 

 the bisporangiate fructification of the Bennettitales to the magnolia 

 type of flower does not seem adequate for establishing such a rela- 

 tionship, and so we must conclude that the Bennettitales were the 

 last of their line; they left no progeny. 



