334 



THE AMEBIC AN NATURALIST [Vol, LV 



base of purpurea as a modified petiolate condition, but as 

 a matter of fact our studies have shown that its affinities 

 in this respect lie closer to the sessile leaf type gentically, 

 to which it is recessive, than to the true petiolate class 

 which is dominant to the sessile type. In the present 

 article we show further that the flower colors of macro- 

 phylla and purpurea are distinctly dii¥erent genetically 

 and their similarity in appearance can not be regarded 

 as an indication of phylogenetic relationship. It is, there- 

 fore, evident that any taxonomic system which proposes 

 to portray the phylogenetic affinities of the polymorphic 

 assemblage of Tabacum varieties must be derived from 

 genetic studies of character differences. 



Allard has suggested the use of these flower color forms 

 for instructional work in genetics. The demonstration 

 of these additional relations increases their interest and 

 value for such purposes. Among other points of interest 

 a cross between macrophylla and purpurea should give 

 a carmine Fj and the rather unusual segregation ratio 

 of 13 carmine (and red): 3 pink. We have verified the 

 production of carmine Fj in this cross, but have not yet 

 grown the Fg progeny. The ease of hyl)ri<lizati()ii. the 

 readiness with which large quantities of liuardcd seed 

 may be secured, and the extremely long period over which 

 the seed of tobacco retains its viability may be urged as 

 additional advantages in its utilization. Where green- 

 house and garden space is available for their growth- 

 plants may easily be grown to maturity in six-inch pots— 

 these varieties and their hybrids would provide excellent 

 material for practise in hybridization and for demonstra- 

 tions of segregation and unique character interrelations. 

 While there is a certain amount of variation within the 

 several phenotypes here considci-cd. \ i/.. caiiiiino, red, 

 pink, and white, it has not been found to interfere 

 seriously with segregation into the main color classes. 



