EMBRYOGENESIS IN FLOWERING PLANTS 



267 



embryonic development, the reaction system could have been modified 

 so as to yield this new type of organisation. It has also to be borne in 

 mind that the monocotyledons may be a polyphyletic group, and that 



Fig. 69. Lilaea subulata 



Stages in the development of the embryo; the basal cell enlarges but does not 

 undergo further divisions; the terminal cell divides and gives rise to a large globular 

 to ellipsoidal mass of cells; eventually there is a single massive cotyledon, the 

 lateral shoot apex and the basal root only differentiating at a later stage ( x 330, 



after Agrawal). 



some lines may have diverged from a very primitive dicotyledonous 

 source and others from a more advanced source. It may also be worth 

 pondering whether the kind of mutation that led to the inception of the 



