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THE AMERICAN NATURALIST [Vol. XLVIII 



crossing taken place in the case of the unguarded flowers, 

 this would, because of the purely recessive characters 

 possessed by simplex, have become apparent at once. In 

 all cases the parents were checked by means of herbarium 

 specimens or photographs, or both. 



2. bbNN (square 11). According to our hypothesis, a 

 plant of this zygotic construction should have the earlier 

 roset leaves narrow and the climax leaves should lack 

 incisions to the midrib. It also should breed true. A 

 plant fulfilling these conditions has not been encountered, 

 or rather, its recognition was delayed until the offspring 

 of the corresponding heterozygote l>l>Xn could be observed. 

 As will be shown, the zygotic combination bbNN yields 

 a plant with the external characteristics of arachnoidea. 



3. bbNn (squares 12 and 15). A plant of this zygotic 

 constitution should have narrow early leaves and the 

 climax leaves should lack incisions to the midrib. On 

 self-fertilization it should yield 25 per cent. bbNN, 50 

 per cent. bbN)i and 25 per cent. bbnn. 



Several plants were found which fulfilled the require- 

 ments as to leaf characters. Such plants, on being selfed, 

 yielded approximately 25 per cent, simpler, which we 

 know to have the zygotic constitution bbnn, while about 

 50 per cent, bore the parental characters, supposedly rep- 

 resented by bbNn. The remaining 25 per cent, clearly 

 belonged to the type arachnoidea. In all, 12 plants were 

 selected as seed bearers, some being guarded, others re- 

 maining uncaged. The results are given in Table II. 



The totals closely approximate the Mendelian ratio, 

 yielding, respectively, b bNN 24 per cent., bbNn 49 percent, 

 and bbnn 27 per cent. Having established the identity 

 of bbnn (simplex) and bbNn {attenuata), we are forced 

 to recognize bbNN as the zygotic construction of arach- 

 noidea. It would be a comparatively easy matter to test 



