Examples of Constant Races. 



79 



amples of this are the Discoidea forms of many com- 

 posites. 



MoQUiN Tandon regarded the Discoidea, i. e., the 

 form without tongue-florets, as the Peloria of the Com- 

 posites.^ They are generally regarded as having arisen 

 from the Radiata forms. Sometimes the discoid form is 



Fig. 8. Scnecio Jacohaea L. (f. radiata). 



commoner than that with rays, and then the Discoidea 



form may be found described in systematic works as a 



species and the Radiata as the variety ; as for instance in 



Bidens tripartita (Fig. 7), and B. cernua,^ although B. 



^ Teratologic vegetate, p. 179. 



^ Koch, Synopsis Florae Geniiauieae, p. 309. 



