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 the F; hybrids of N. tabacum “Cuba” and 
sylvestris. 
Fie. 103.—Nicotiana sylvestris (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 F;, the sesqui-hybrids thus obtained are of diverse types, most 
of them abnormal, but about 10 per cent. closely approximate N. 
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