380 



The Journal of Heredity 



PARENT TYPE OF THE CACTUS DAHLIA 



Figure 23. All of our cactus dahlias trace back to a single plant sent to Europe from 

 Mexico about 1863. This plant was also taken as the type of a new species of dahlia, 

 jaurecii, but the simpler ancestral form remained unknown until the single, eight-rayed 

 type shown in Figure 22 was discovered by Mr. Popenoe. 



of cultivation. The flower-heads of 

 both were "double," and both were an- 

 cestors of many varieties. So diverse 

 were the seedlings of Dahlia pinnata 

 that it was renamed Dahlia variabilis; 

 but according to the rules of priority, 

 its older name must be retained. For 

 the same reason the name Dahlia rosea, 

 also a synonym of Dahlia pinnata, must 

 also be discarded. The many varieties 

 of dahlias with rounded artificial-look- 

 ing heads, formerly so common in 

 gardens were all descendents of Dahlia 



pinnata. Dahlia coccinca offered a strik- 

 ing contrast to these in resisting all 

 eft'orts of plant breeders to cross-polli- 

 nate it with them, and also in coming 

 true to seed. Its heads are single ; its 

 color varies from scarlet to yellow or 

 brownish red, never verging upon pink 

 or crimson. 



The idea has commonly prevailed for 

 a long time that duplex and double forms 

 were the result of recent cultivation ; 

 but it is quite certain that they were 

 well known to the Aztecs, who domes- 



