412 MORPHOLOGY OF THE ANGIOSPERMS 



primitive and highly advanced characters, but some characters have 

 been obscured by reduction in adaptation to an aquatic habit. 



The stamens are primitive in form — no differentiation of anthers and 

 filaments, and four elongate sporangia, median on the abaxial side 

 (Fig. 49). The stamens, however, cannot be considered primitive on 

 the basis of form alone, for simplicity of form may represent modifica- 

 tion in adaptation to pollination under water. But the close similarity 

 in form to stamens of the woody Ranales that are undoubtedly primi- 

 tive is remarkable. In the abaxial position of the sporangia, the stamens 

 further resemble some primitive ranahan types, but the significance of 

 this character is unknown. 



The gynoecium, in contrast with the androecium, shows high spe- 

 cialization — a solitary carpel with one ovule, which is borne distally on 

 the dorsal side (Fig. 85C). The position of the ovule is evidence that 

 reduction in ovule number has been directly from laminar placentation; 

 this gynoecial character strengthens other evidence of primitiveness for 

 the family. 



The embryo has been described as "multicotyledonary, a remarkable 

 type suggestive of the polycotyledonary embryos of some conifers." 

 (Conifer embryos with more than two cotyledons have been shown to 

 be specialized types.) But the embryo of CemfophyUum has been 

 shown to be a normal dicotyledonous embryo, with the plumule rather 

 well developed in the seed, and the "extra" cotyledons to be the 

 primordia of the first leaves. 



The Ceratophyllaceae are an isolated family, with, apparently, little 

 evidence of relationship to other dicotyledonous families. It has been 

 frequently suggested that they are related to the Nymphaeaceae and 

 Cabombaceae, but this relationship seems unlikely, because of the 

 abaxial microsporangia and whorled leaves in the Ceratophyllaceae. 

 Resemblance in placentation — dorsal attachment of ovules in Cabomba 

 and Ceratophtjlliim — is unimportant; all have laminar placentation 

 basically. The single integument of the ovule has been considered pos- 

 sible evidence of relationship to several famifies in the dicotyledons 

 and to the Najadaceae among the monocotyledons, but ovules with one 

 integument represent a frequent reduction type, especially in aquatic 

 and parasitic taxa. A possibly significant character is the abaxial posi- 

 tion of the microsporangia in Cabomba and CerafoplujUtim, but Brasenia 

 and the Nymphaeaceae — probably relatives of Cabomba — have adaxial 

 microsporangia. 



Ranunculaceae 



The Ranunculaceae are remarkable for their many combinations of 

 primitive and advanced characters. The flowers are primitive in their 



