FLAX AND TOBACCO 161 



from selfing these self-sterile species are spoken of as cases of 

 pseudo-fertility. 



Results of crosses between self sterile and self fertile varieties 

 are given in Table XXXVI: 



TABLE XXXVI. INHERITANCE OF STERILITY IN CROSSES BETWEEN SELF- 

 FERTILE AND SELF STERILE TOBACCO SPECIES 

 PABENTS Fi F 2 



Forgetiana X Langsdorffii Self -fertile 144 self-: 37 self- 

 vigorous fertile sterile 



Alata X Langsdorffii ' Self -fertile 162 self-: 38 self- 

 vigorous fertile sterile 



The self -fertile condition proved dominant in FI and a ratio of 

 approximately 4 self-fertile to 1 self-sterile plant was obtained 

 in F 2 . The self -sterile plants of F 2 proved self -sterile in later 

 generation's. East explained these results by a dominant factor, 

 F, for fertility and a subsidiary factor, D, for pseudo-fertility 

 which exhibits itself only in the presence of the factors for sterility, 

 ff. This pseudo-fertility factor produces some fertility under 

 certain conditions, thus tending to lower the number of self-sterile 

 forms. 



East has suggested that differences in the rate of pollen 

 germination are largely responsible for the differences in the 

 length of pollen tubes from compatible and incompatible pollina- 

 tions. When self-sterile plants are self-pollinated the pollen 

 grains germinate but the pollen tubes grow so slowly that abscis- 

 sion of the flower occurs before the pollen tube reaches the ovary. 



Color Characters. Color of corolla has been studied for Nico- 

 tiana crosses. East (19166) found that in crosses between N. 

 Langsdorffii and N. alata there was a dominance in F\ of yellow 

 over white in the color of the corolla. The Langsdorffii parent 

 produces blue pollen and the alata yellow. Reciprocal crosses 

 gave blue pollen in FI, although the color was somewhat lighter 

 than in the blue-pollen parent. Results in F 2 showed 342 

 plants with blue pollen and 100 plants with yellow pollen. Yel- 

 low-pollen plants bred true in F 3 . Here we have a cross between 

 species which exhibits a monohybrid ratio. 



According to Allard (1919a) N. tabacum exhibits three distinct 

 flower colors carmine, pink, and white. In crosses between car- 

 mine and pink theFi was carmine. The FI pollinated with the car- 

 mine parent gave all carmine colored progeny while the FI crossed 

 11 



