218 



THE WATERLILIES. 



changed less than its fellow Castalias, whereas N. odorata by its rich odor, 

 and N. tuberosa by its rhizome show marked specialization as compared 

 with any other species of Nymphaea. Finally, in the American tropics, 

 Hydrocallis has arisen from the Castalia stock. This group is too little 

 known to assign relationships among the species, but it is probable that 



N.GIGANTEA 



N.2AN2I8ARIENSI5 



N.O.GIGANTEA 



ANOECTOMmiA 



fYMPHAFITE POLYRHI2US 



NFLUMBONEAE 



N. amazonnm, rtidgeana, and blanda are lower and N. oxypetala one of the 

 highest forms. While these were developing, the genus as a whole was 

 being pushed southward by the increasing coldness of the polar region, 

 until the present distribution was brought about. The above diagram 

 indicates graphically the proposed relationships of the species. 



