518 University of California Publications in Botany [Vol. 5 



varieties angustifolia and virginica have lively pink flowers. Of the 

 paler pinks or "pinkish" forms we have a representative in our A". 

 Tahacum var. Cavala, U. C. B. G. 12/05, which has flowers distinctly 

 lighter in color than those of angustifolia or virginica. Our petiolate 

 forms also seem to be of different constitution from those with which 

 Miss Howard worked, for she presents evidence to show that hers are 

 combinations of recessive factors and that they breed true whenever 

 they occur as segregation products, whereas our petiolate forms often 

 gave plants with sessile leaves as segregation products. We have, 

 however, secured evidence that some distinctly short petiolate forms 

 arise from sessile ones, perhaps by modifications of the auriculata 

 leaf type in the direction of stripping the auricle and lower portion 

 of the lamina from such leaves, but our results are not yet definite 

 enough to permit of rigid formulation. Further investigation of the 

 relationships of the various petiolate forms is necessary. 



As respects flower color Allard (1919) has presented some inter- 

 esting data which at first sight appear to contradict those which we 

 have presented. Allard found that carmine x pink gave F^ carmine and 

 Fo 3 carmine : 1 pink. The back crosses gave consistent data. Thus 

 F^ carmine x carmine parent gave all carmine, and F^ carmine x pink 

 parent gave 1 carmine : 1 pink. In F, pink segregants bred true for 

 pink, and carmine either bred true for carmine or gave again 3 carmine 

 :1 pink. The difficulty here is that our red is not genetically identical 

 with Allard 's carmine. Our flowers of macrophylla and calycina at 

 full expansion show a color lying between rose red and pomegranate 

 purple of the Ridgway color scale. This color, which we have called 

 red for the sake of brevity, is very close to carmine, but we have an- 

 other flower color, which we call dark red, represented by N. Tahacum 

 var. mucrophylla purpurea, which is probably identical with the Giant 

 Red flowering tobacco which Allard used in his experiments. 



We have made some preliminary tests of this dark red, and find 

 that it behaves differently from red. Crossed with our white it gives 

 dark red in F^, instead of pink as was obtained from red x white. 

 Since our white carries the factor R, which is responsible for the 

 production of pink flower color, dark red must differ from pink in a 

 dominant factor. If %ve call this factor pair Pp, then our various 

 colors of tobacco would have the following genotypes : 



Dark red WWRRPP 



Red WWrrpp 



Pink WWRRpp 



White ww^RRpp 



