58 postelsia 



An hypothesis concerning the phy- 

 logeny of any organ involves the phy- 

 logeny of the organisms possessing that 

 organ, in this case the Angiosperms. 

 That the Monocotyledons and Dicoty- 

 ledons have a common ancestry there 

 is no reason to doubt. One would 

 hardly suppose that the similar com- 

 plicated cytological phenomena of em- 

 bryo-sac development and endosperm 

 formation were simply parallelisms in 

 two groups of different phylogenetic 

 origin. The once credited theory how- 

 ever, that the Angiosperms were de- 

 rived from Gymnosperm stock, receives 

 little support in the light of modern 

 research ; the evidence now obtainable 

 pointing rather to the separate genetic 

 origin of these two groups from pteri- 

 dophytic stock. Any discussion as to 

 whether they represent diverging lines 

 from an originally seed-bearing an- 



