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THE AMERICAN NATURALIST [Vol. XLIX 



plants. For these reasons he regards self-fertility as a 

 simple Mendelian dominant to self-sterility in the case 

 studied. I believe Compton would draw no such sharp 

 line about self-sterility in general. In fact, he follows 

 Jost in suggesting the presence of a diffusible substance 

 in the tissues of the style and stigma which retards or 

 promotes pollen tube growth after self-pollination or 

 cross-pollination in some manner analogous to the mech- 

 anism that promotes animal immunity or susceptibility 

 after infection. 



The only alternative general hypothesis has been pro- 

 posed by Morgan, and this can be discussed more advan- 

 tageously after the presentation of my own work, of which 

 only an abstract will be given at this time. 



In 1909 I made a cross between a small red-flowered 

 Nicotiana, Nicotiana forgetiana (Hort.) Sand, and the 

 large white-flowered Nicotiana of the garden Nicotiana 

 alata Lk. and Otto. var. grandiflora Comes. All of the 

 plants of the F x generation appeared to be self-sterile. 

 Tests of Nicotiana forgetiana 2 have shown these plants 

 also to be self-sterile, but both self-fertile and self-sterile 

 plants of the other parent have been found. From data 

 gathered later, there seems to be no doubt that a self- 

 sterile plant of Nicotiana alata grandiflora was used in 

 the actual cross. This conclusion seems reasonable in 

 view of the fact that of over 500 plants of the F 1? F 2 , F 3 

 and F 4 generations tested, not a single self-fertile plant 

 was found. 



The plants of the F x generation were all vigorous and 

 healthy, and in spite of the fact that they resulted from a 

 species cross which Jeffrey claims always produces large 

 amounts of abnormal pollen, a large number of examina- 

 tions of pollen from different individuals showed from 90 



2 I thought originally that both of these species (East, 1913) were self- 

 fertile. Seed had been obtained from a carefully bagged inflorescence of 

 each species in 1909. Either the plant of N. forgetiana which gave this 



