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THE AMERICAN NATURALIST [Vol. XLVIII 



nine sixteenths of the total offspring ami may be uniform 

 in appearance, the constituents being separable only by 

 breeding, "cine heillose Arbeit," as Baur has it. For- 

 tunately, in this case, it is possible to distinguish readily 

 between the various combinations. 



One of the combinations, BBNN (square 1), should 

 breed true, being homozygotic for both characters con- 

 cerned. We would expect such a plant to have narrow 

 first leaves and climax leaves with incisions to the mid- 

 rib. Thus far I have not encountered such a plant, some- 

 thing which at one time led me to consider the possibility 

 of gametic repulsion, in this instance the gamete BN 

 being incapable of existence. This supposition seemed 

 the more plausible since the two genes B and N well might 

 be supposed to be antagonistic, the one being responsible 

 for an incision of the leaf to the midrib, the other tending 

 to make the leaf, especially the earlier leaves, narrow. 

 Were this assumption correct, none of the zygotic combi- 

 nations found in squares 1, 2 and 5, 3 and 9, and 4 and 13, 

 would be formed, though we would expect the same com- 

 bination as occurs in squares 4 and 13 to make its appear- 

 ance as the result of the fusion of the gametes bN and 

 Bn (squares 7 and 10). 



Were this supposition correct, we should have a case 

 similar to that of the sweet pea "Purple Invincible," and 

 we could not expect the gamete (bn) to be formed. Since, 

 however, simpler (bbnn) appears in our cultures, this 

 theory must be rejected. Recently also, in culture No. 

 30,412, an instance was found in which the guarded parent, 

 supposedly of type 4, yielded, not simpler, rhomboidea, 

 attenuata, arachnoid ea as well as the parental type, but 

 only arachnoidea, rhomboidea and the parental type, and 

 in proportions closely approximating a ratio 1:1:2. 



A plant which yielded 25 per cent, rhomboidea and no 

 simplex, must have been homozygotic for B, and since it 

 yielded also 50 per cent, of type 4. must have been hetero- 

 zygotic for N, its zygotic constitution therefore being 

 BBNn. Such a plant, on self-fertilization, should yield 

 25 per cent, rhomboidea. Provided the homozygote and 



