164 A. H. Graves, The Morphology of Ruppta Maritima. 



Ruppia is closer to Potamogeton, Zannichellia, and Althenia than to 

 any others of the Potamogetonaceae, especially with regard to the 

 vegetative organs ; and yet, in its embryo, it most strongly resem- 

 bles Zostera. Similarities in the vascular structure of the vegetative 

 organs are looked upon generally as comparativel}' fixed indications 

 of relationship ; so that in this case the evidence points to Ruppia 

 as being derived from some form similar to the present submerged 

 Potamogetons, with Zannichellia and Althenia serving as examples 

 of still further reduction. 



