264 



EMBRYOGENESIS IN PLANTS 



dicotyledonous or polycotyledonous form and that they afford 

 evidence of deviation from the ancestral form during the early stages of 

 their ontogenetic development; i.e. the process must have involved 

 the substitution of one cotyledon for two during the embryogeny. 



Ranunculus ficaria has attracted the attention of both taxonomists 

 and embryologists because of the presence of certain monocotyledonous 



ca 



cb 



^ 



© 



Fig. 67. Embryonic development in Ranunculus ficaria up to the 



time of shedding of seed (after Soueges) 



The initial embryogeny, though sometimes irregular, is in general like that of 



Myosiirus, Fig. 56. 



characters in the morphology and anatomy of the adult plant and of a 

 single cotyledon in the fully developed embryo. As Soueges (1913) and 

 others have shown, the early stages in the embryogeny, though often 

 irregular and frequently abortive, are in general agreement with those 

 for other Ranunculaceae, e.g. Myosurus, Fig. 56a-e. At the time of 

 seed dispersal the embryo is still in the proembryo phase, its further 

 development taking place on seed germination. The development of 

 the distal region of the embryo proper is such that it has only one 

 longitudinal plane of symmetry. Johansen's account (1950) is as 

 follows : 



'The upper region of the embryo is the first to commence 

 development. This becomes slightly indented at the apex, concave 



