240 



GENETICS IN RELATION TO AGRICULTURE 



rently a recessive character in crosses with N. tabacum varieties which 

 display a normal behavior in this respect, but it is manifested in the F\ 

 hybrids with N. sylvestris in the remarkable way in which this hybrid 

 retains its seed capsules, although there are very few or no seeds in them. 

 Since all the other F\ hybrids of tabacum varieties and sylvestris shed their 

 flowers, often before the corolla has withered, this feature has very 

 conspicuously characterized theFi hybrids of N. tabacum "Cuba" and 

 sylvestris. 



Fia. 103. Nicotiana sylvestna (left), N. tabacum angustifolia (right) and the Fi hybrid 

 (center). (After Goodspeed and Clausen.) 



The significant feature of these hybrids, however, is the hereditary 

 behavior which they display. They are almost completely sterile, but 

 if the plants are grown under reduced conditions of culture and the flowers 

 are hand pollinated with pollen from either of the parent species, a few 

 seeds are set, but not more than about 1 per cent, of the number ordi- 

 narily produced by the parents. If N. sylvestris pollen is used to polli- 

 nate the FI, the sesqui-hybrids thus obtained are of diverse types, most 

 of them abnormal, but about 10 per cent, closely approximate N. 



